Adding upstream version 14.5.upstream/14.5upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

13 files changed, 19460 insertions, 0 deletions

diff --git a/src/backend/replication/logical/Makefile b/src/backend/replication/logical/Makefile
new file mode 100644
index 0000000..c4e2fde
--- /dev/null
+++ b/src/backend/replication/logical/Makefile
@@ -0,0 +1,31 @@
+#-------------------------------------------------------------------------
+#
+# Makefile--
+#    Makefile for src/backend/replication/logical
+#
+# IDENTIFICATION
+#    src/backend/replication/logical/Makefile
+#
+#-------------------------------------------------------------------------
+
+subdir = src/backend/replication/logical
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+
+override CPPFLAGS := -I$(srcdir) $(CPPFLAGS)
+
+OBJS = \
+	decode.o \
+	launcher.o \
+	logical.o \
+	logicalfuncs.o \
+	message.o \
+	origin.o \
+	proto.o \
+	relation.o \
+	reorderbuffer.o \
+	snapbuild.o \
+	tablesync.o \
+	worker.o
+
+include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
new file mode 100644
index 0000000..92dfafc
--- /dev/null
+++ b/src/backend/replication/logical/decode.c
@@ -0,0 +1,1316 @@
+/* -------------------------------------------------------------------------
+ *
+ * decode.c
+ *		This module decodes WAL records read using xlogreader.h's APIs for the
+ *		purpose of logical decoding by passing information to the
+ *		reorderbuffer module (containing the actual changes) and to the
+ *		snapbuild module to build a fitting catalog snapshot (to be able to
+ *		properly decode the changes in the reorderbuffer).
+ *
+ * NOTE:
+ *		This basically tries to handle all low level xlog stuff for
+ *		reorderbuffer.c and snapbuild.c. There's some minor leakage where a
+ *		specific record's struct is used to pass data along, but those just
+ *		happen to contain the right amount of data in a convenient
+ *		format. There isn't and shouldn't be much intelligence about the
+ *		contents of records in here except turning them into a more usable
+ *		format.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/decode.c
+ *
+ * -------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/heapam.h"
+#include "access/heapam_xlog.h"
+#include "access/transam.h"
+#include "access/xact.h"
+#include "access/xlog_internal.h"
+#include "access/xlogreader.h"
+#include "access/xlogrecord.h"
+#include "access/xlogutils.h"
+#include "catalog/pg_control.h"
+#include "replication/decode.h"
+#include "replication/logical.h"
+#include "replication/message.h"
+#include "replication/origin.h"
+#include "replication/reorderbuffer.h"
+#include "replication/snapbuild.h"
+#include "storage/standby.h"
+
+typedef struct XLogRecordBuffer
+{
+	XLogRecPtr	origptr;
+	XLogRecPtr	endptr;
+	XLogReaderState *record;
+} XLogRecordBuffer;
+
+/* RMGR Handlers */
+static void DecodeXLogOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeStandbyOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+
+/* individual record(group)'s handlers */
+static void DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeUpdate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeDelete(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeTruncate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeMultiInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeSpecConfirm(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+
+static void DecodeCommit(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
+						 xl_xact_parsed_commit *parsed, TransactionId xid,
+						 bool two_phase);
+static void DecodeAbort(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
+						xl_xact_parsed_abort *parsed, TransactionId xid,
+						bool two_phase);
+static void DecodePrepare(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
+						  xl_xact_parsed_prepare *parsed);
+
+
+/* common function to decode tuples */
+static void DecodeXLogTuple(char *data, Size len, ReorderBufferTupleBuf *tup);
+
+/* helper functions for decoding transactions */
+static inline bool FilterPrepare(LogicalDecodingContext *ctx,
+								 TransactionId xid, const char *gid);
+static bool DecodeTXNNeedSkip(LogicalDecodingContext *ctx,
+							  XLogRecordBuffer *buf, Oid dbId,
+							  RepOriginId origin_id);
+
+/*
+ * Take every XLogReadRecord()ed record and perform the actions required to
+ * decode it using the output plugin already setup in the logical decoding
+ * context.
+ *
+ * NB: Note that every record's xid needs to be processed by reorderbuffer
+ * (xids contained in the content of records are not relevant for this rule).
+ * That means that for records which'd otherwise not go through the
+ * reorderbuffer ReorderBufferProcessXid() has to be called. We don't want to
+ * call ReorderBufferProcessXid for each record type by default, because
+ * e.g. empty xacts can be handled more efficiently if there's no previous
+ * state for them.
+ *
+ * We also support the ability to fast forward thru records, skipping some
+ * record types completely - see individual record types for details.
+ */
+void
+LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *record)
+{
+	XLogRecordBuffer buf;
+	TransactionId txid;
+
+	buf.origptr = ctx->reader->ReadRecPtr;
+	buf.endptr = ctx->reader->EndRecPtr;
+	buf.record = record;
+
+	txid = XLogRecGetTopXid(record);
+
+	/*
+	 * If the top-level xid is valid, we need to assign the subxact to the
+	 * top-level xact. We need to do this for all records, hence we do it
+	 * before the switch.
+	 */
+	if (TransactionIdIsValid(txid))
+	{
+		ReorderBufferAssignChild(ctx->reorder,
+								 txid,
+								 record->decoded_record->xl_xid,
+								 buf.origptr);
+	}
+
+	/* cast so we get a warning when new rmgrs are added */
+	switch ((RmgrId) XLogRecGetRmid(record))
+	{
+			/*
+			 * Rmgrs we care about for logical decoding. Add new rmgrs in
+			 * rmgrlist.h's order.
+			 */
+		case RM_XLOG_ID:
+			DecodeXLogOp(ctx, &buf);
+			break;
+
+		case RM_XACT_ID:
+			DecodeXactOp(ctx, &buf);
+			break;
+
+		case RM_STANDBY_ID:
+			DecodeStandbyOp(ctx, &buf);
+			break;
+
+		case RM_HEAP2_ID:
+			DecodeHeap2Op(ctx, &buf);
+			break;
+
+		case RM_HEAP_ID:
+			DecodeHeapOp(ctx, &buf);
+			break;
+
+		case RM_LOGICALMSG_ID:
+			DecodeLogicalMsgOp(ctx, &buf);
+			break;
+
+			/*
+			 * Rmgrs irrelevant for logical decoding; they describe stuff not
+			 * represented in logical decoding. Add new rmgrs in rmgrlist.h's
+			 * order.
+			 */
+		case RM_SMGR_ID:
+		case RM_CLOG_ID:
+		case RM_DBASE_ID:
+		case RM_TBLSPC_ID:
+		case RM_MULTIXACT_ID:
+		case RM_RELMAP_ID:
+		case RM_BTREE_ID:
+		case RM_HASH_ID:
+		case RM_GIN_ID:
+		case RM_GIST_ID:
+		case RM_SEQ_ID:
+		case RM_SPGIST_ID:
+		case RM_BRIN_ID:
+		case RM_COMMIT_TS_ID:
+		case RM_REPLORIGIN_ID:
+		case RM_GENERIC_ID:
+			/* just deal with xid, and done */
+			ReorderBufferProcessXid(ctx->reorder, XLogRecGetXid(record),
+									buf.origptr);
+			break;
+		case RM_NEXT_ID:
+			elog(ERROR, "unexpected RM_NEXT_ID rmgr_id: %u", (RmgrIds) XLogRecGetRmid(buf.record));
+	}
+}
+
+/*
+ * Handle rmgr XLOG_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeXLogOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	SnapBuild  *builder = ctx->snapshot_builder;
+	uint8		info = XLogRecGetInfo(buf->record) & ~XLR_INFO_MASK;
+
+	ReorderBufferProcessXid(ctx->reorder, XLogRecGetXid(buf->record),
+							buf->origptr);
+
+	switch (info)
+	{
+			/* this is also used in END_OF_RECOVERY checkpoints */
+		case XLOG_CHECKPOINT_SHUTDOWN:
+		case XLOG_END_OF_RECOVERY:
+			SnapBuildSerializationPoint(builder, buf->origptr);
+
+			break;
+		case XLOG_CHECKPOINT_ONLINE:
+
+			/*
+			 * a RUNNING_XACTS record will have been logged near to this, we
+			 * can restart from there.
+			 */
+			break;
+		case XLOG_NOOP:
+		case XLOG_NEXTOID:
+		case XLOG_SWITCH:
+		case XLOG_BACKUP_END:
+		case XLOG_PARAMETER_CHANGE:
+		case XLOG_RESTORE_POINT:
+		case XLOG_FPW_CHANGE:
+		case XLOG_FPI_FOR_HINT:
+		case XLOG_FPI:
+		case XLOG_OVERWRITE_CONTRECORD:
+			break;
+		default:
+			elog(ERROR, "unexpected RM_XLOG_ID record type: %u", info);
+	}
+}
+
+/*
+ * Handle rmgr XACT_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	SnapBuild  *builder = ctx->snapshot_builder;
+	ReorderBuffer *reorder = ctx->reorder;
+	XLogReaderState *r = buf->record;
+	uint8		info = XLogRecGetInfo(r) & XLOG_XACT_OPMASK;
+
+	/*
+	 * If the snapshot isn't yet fully built, we cannot decode anything, so
+	 * bail out.
+	 */
+	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT)
+		return;
+
+	switch (info)
+	{
+		case XLOG_XACT_COMMIT:
+		case XLOG_XACT_COMMIT_PREPARED:
+			{
+				xl_xact_commit *xlrec;
+				xl_xact_parsed_commit parsed;
+				TransactionId xid;
+				bool		two_phase = false;
+
+				xlrec = (xl_xact_commit *) XLogRecGetData(r);
+				ParseCommitRecord(XLogRecGetInfo(buf->record), xlrec, &parsed);
+
+				if (!TransactionIdIsValid(parsed.twophase_xid))
+					xid = XLogRecGetXid(r);
+				else
+					xid = parsed.twophase_xid;
+
+				/*
+				 * We would like to process the transaction in a two-phase
+				 * manner iff output plugin supports two-phase commits and
+				 * doesn't filter the transaction at prepare time.
+				 */
+				if (info == XLOG_XACT_COMMIT_PREPARED)
+					two_phase = !(FilterPrepare(ctx, xid,
+												parsed.twophase_gid));
+
+				DecodeCommit(ctx, buf, &parsed, xid, two_phase);
+				break;
+			}
+		case XLOG_XACT_ABORT:
+		case XLOG_XACT_ABORT_PREPARED:
+			{
+				xl_xact_abort *xlrec;
+				xl_xact_parsed_abort parsed;
+				TransactionId xid;
+				bool		two_phase = false;
+
+				xlrec = (xl_xact_abort *) XLogRecGetData(r);
+				ParseAbortRecord(XLogRecGetInfo(buf->record), xlrec, &parsed);
+
+				if (!TransactionIdIsValid(parsed.twophase_xid))
+					xid = XLogRecGetXid(r);
+				else
+					xid = parsed.twophase_xid;
+
+				/*
+				 * We would like to process the transaction in a two-phase
+				 * manner iff output plugin supports two-phase commits and
+				 * doesn't filter the transaction at prepare time.
+				 */
+				if (info == XLOG_XACT_ABORT_PREPARED)
+					two_phase = !(FilterPrepare(ctx, xid,
+												parsed.twophase_gid));
+
+				DecodeAbort(ctx, buf, &parsed, xid, two_phase);
+				break;
+			}
+		case XLOG_XACT_ASSIGNMENT:
+
+			/*
+			 * We assign subxact to the toplevel xact while processing each
+			 * record if required.  So, we don't need to do anything here. See
+			 * LogicalDecodingProcessRecord.
+			 */
+			break;
+		case XLOG_XACT_INVALIDATIONS:
+			{
+				TransactionId xid;
+				xl_xact_invals *invals;
+
+				xid = XLogRecGetXid(r);
+				invals = (xl_xact_invals *) XLogRecGetData(r);
+
+				/*
+				 * Execute the invalidations for xid-less transactions,
+				 * otherwise, accumulate them so that they can be processed at
+				 * the commit time.
+				 */
+				if (TransactionIdIsValid(xid))
+				{
+					if (!ctx->fast_forward)
+						ReorderBufferAddInvalidations(reorder, xid,
+													  buf->origptr,
+													  invals->nmsgs,
+													  invals->msgs);
+					ReorderBufferXidSetCatalogChanges(ctx->reorder, xid,
+													  buf->origptr);
+				}
+				else if ((!ctx->fast_forward))
+					ReorderBufferImmediateInvalidation(ctx->reorder,
+													   invals->nmsgs,
+													   invals->msgs);
+			}
+			break;
+		case XLOG_XACT_PREPARE:
+			{
+				xl_xact_parsed_prepare parsed;
+				xl_xact_prepare *xlrec;
+
+				/* ok, parse it */
+				xlrec = (xl_xact_prepare *) XLogRecGetData(r);
+				ParsePrepareRecord(XLogRecGetInfo(buf->record),
+								   xlrec, &parsed);
+
+				/*
+				 * We would like to process the transaction in a two-phase
+				 * manner iff output plugin supports two-phase commits and
+				 * doesn't filter the transaction at prepare time.
+				 */
+				if (FilterPrepare(ctx, parsed.twophase_xid,
+								  parsed.twophase_gid))
+				{
+					ReorderBufferProcessXid(reorder, parsed.twophase_xid,
+											buf->origptr);
+					break;
+				}
+
+				/*
+				 * Note that if the prepared transaction has locked [user]
+				 * catalog tables exclusively then decoding prepare can block
+				 * till the main transaction is committed because it needs to
+				 * lock the catalog tables.
+				 *
+				 * XXX Now, this can even lead to a deadlock if the prepare
+				 * transaction is waiting to get it logically replicated for
+				 * distributed 2PC. Currently, we don't have an in-core
+				 * implementation of prepares for distributed 2PC but some
+				 * out-of-core logical replication solution can have such an
+				 * implementation. They need to inform users to not have locks
+				 * on catalog tables in such transactions.
+				 */
+				DecodePrepare(ctx, buf, &parsed);
+				break;
+			}
+		default:
+			elog(ERROR, "unexpected RM_XACT_ID record type: %u", info);
+	}
+}
+
+/*
+ * Handle rmgr STANDBY_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeStandbyOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	SnapBuild  *builder = ctx->snapshot_builder;
+	XLogReaderState *r = buf->record;
+	uint8		info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
+
+	ReorderBufferProcessXid(ctx->reorder, XLogRecGetXid(r), buf->origptr);
+
+	switch (info)
+	{
+		case XLOG_RUNNING_XACTS:
+			{
+				xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
+
+				SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+
+				/*
+				 * Abort all transactions that we keep track of, that are
+				 * older than the record's oldestRunningXid. This is the most
+				 * convenient spot for doing so since, in contrast to shutdown
+				 * or end-of-recovery checkpoints, we have information about
+				 * all running transactions which includes prepared ones,
+				 * while shutdown checkpoints just know that no non-prepared
+				 * transactions are in progress.
+				 */
+				ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+			}
+			break;
+		case XLOG_STANDBY_LOCK:
+			break;
+		case XLOG_INVALIDATIONS:
+
+			/*
+			 * We are processing the invalidations at the command level via
+			 * XLOG_XACT_INVALIDATIONS.  So we don't need to do anything here.
+			 */
+			break;
+		default:
+			elog(ERROR, "unexpected RM_STANDBY_ID record type: %u", info);
+	}
+}
+
+/*
+ * Handle rmgr HEAP2_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	uint8		info = XLogRecGetInfo(buf->record) & XLOG_HEAP_OPMASK;
+	TransactionId xid = XLogRecGetXid(buf->record);
+	SnapBuild  *builder = ctx->snapshot_builder;
+
+	ReorderBufferProcessXid(ctx->reorder, xid, buf->origptr);
+
+	/*
+	 * If we don't have snapshot or we are just fast-forwarding, there is no
+	 * point in decoding changes.
+	 */
+	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT ||
+		ctx->fast_forward)
+		return;
+
+	switch (info)
+	{
+		case XLOG_HEAP2_MULTI_INSERT:
+			if (!ctx->fast_forward &&
+				SnapBuildProcessChange(builder, xid, buf->origptr))
+				DecodeMultiInsert(ctx, buf);
+			break;
+		case XLOG_HEAP2_NEW_CID:
+			{
+				xl_heap_new_cid *xlrec;
+
+				xlrec = (xl_heap_new_cid *) XLogRecGetData(buf->record);
+				SnapBuildProcessNewCid(builder, xid, buf->origptr, xlrec);
+
+				break;
+			}
+		case XLOG_HEAP2_REWRITE:
+
+			/*
+			 * Although these records only exist to serve the needs of logical
+			 * decoding, all the work happens as part of crash or archive
+			 * recovery, so we don't need to do anything here.
+			 */
+			break;
+
+			/*
+			 * Everything else here is just low level physical stuff we're not
+			 * interested in.
+			 */
+		case XLOG_HEAP2_FREEZE_PAGE:
+		case XLOG_HEAP2_PRUNE:
+		case XLOG_HEAP2_VACUUM:
+		case XLOG_HEAP2_VISIBLE:
+		case XLOG_HEAP2_LOCK_UPDATED:
+			break;
+		default:
+			elog(ERROR, "unexpected RM_HEAP2_ID record type: %u", info);
+	}
+}
+
+/*
+ * Handle rmgr HEAP_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	uint8		info = XLogRecGetInfo(buf->record) & XLOG_HEAP_OPMASK;
+	TransactionId xid = XLogRecGetXid(buf->record);
+	SnapBuild  *builder = ctx->snapshot_builder;
+
+	ReorderBufferProcessXid(ctx->reorder, xid, buf->origptr);
+
+	/*
+	 * If we don't have snapshot or we are just fast-forwarding, there is no
+	 * point in decoding data changes.
+	 */
+	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT ||
+		ctx->fast_forward)
+		return;
+
+	switch (info)
+	{
+		case XLOG_HEAP_INSERT:
+			if (SnapBuildProcessChange(builder, xid, buf->origptr))
+				DecodeInsert(ctx, buf);
+			break;
+
+			/*
+			 * Treat HOT update as normal updates. There is no useful
+			 * information in the fact that we could make it a HOT update
+			 * locally and the WAL layout is compatible.
+			 */
+		case XLOG_HEAP_HOT_UPDATE:
+		case XLOG_HEAP_UPDATE:
+			if (SnapBuildProcessChange(builder, xid, buf->origptr))
+				DecodeUpdate(ctx, buf);
+			break;
+
+		case XLOG_HEAP_DELETE:
+			if (SnapBuildProcessChange(builder, xid, buf->origptr))
+				DecodeDelete(ctx, buf);
+			break;
+
+		case XLOG_HEAP_TRUNCATE:
+			if (SnapBuildProcessChange(builder, xid, buf->origptr))
+				DecodeTruncate(ctx, buf);
+			break;
+
+		case XLOG_HEAP_INPLACE:
+
+			/*
+			 * Inplace updates are only ever performed on catalog tuples and
+			 * can, per definition, not change tuple visibility.  Since we
+			 * don't decode catalog tuples, we're not interested in the
+			 * record's contents.
+			 *
+			 * In-place updates can be used either by XID-bearing transactions
+			 * (e.g.  in CREATE INDEX CONCURRENTLY) or by XID-less
+			 * transactions (e.g.  VACUUM).  In the former case, the commit
+			 * record will include cache invalidations, so we mark the
+			 * transaction as catalog modifying here. Currently that's
+			 * redundant because the commit will do that as well, but once we
+			 * support decoding in-progress relations, this will be important.
+			 */
+			if (!TransactionIdIsValid(xid))
+				break;
+
+			SnapBuildProcessChange(builder, xid, buf->origptr);
+			ReorderBufferXidSetCatalogChanges(ctx->reorder, xid, buf->origptr);
+			break;
+
+		case XLOG_HEAP_CONFIRM:
+			if (SnapBuildProcessChange(builder, xid, buf->origptr))
+				DecodeSpecConfirm(ctx, buf);
+			break;
+
+		case XLOG_HEAP_LOCK:
+			/* we don't care about row level locks for now */
+			break;
+
+		default:
+			elog(ERROR, "unexpected RM_HEAP_ID record type: %u", info);
+			break;
+	}
+}
+
+/*
+ * Ask output plugin whether we want to skip this PREPARE and send
+ * this transaction as a regular commit later.
+ */
+static inline bool
+FilterPrepare(LogicalDecodingContext *ctx, TransactionId xid,
+			  const char *gid)
+{
+	/*
+	 * Skip if decoding of two-phase transactions at PREPARE time is not
+	 * enabled. In that case, all two-phase transactions are considered
+	 * filtered out and will be applied as regular transactions at COMMIT
+	 * PREPARED.
+	 */
+	if (!ctx->twophase)
+		return true;
+
+	/*
+	 * The filter_prepare callback is optional. When not supplied, all
+	 * prepared transactions should go through.
+	 */
+	if (ctx->callbacks.filter_prepare_cb == NULL)
+		return false;
+
+	return filter_prepare_cb_wrapper(ctx, xid, gid);
+}
+
+static inline bool
+FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
+{
+	if (ctx->callbacks.filter_by_origin_cb == NULL)
+		return false;
+
+	return filter_by_origin_cb_wrapper(ctx, origin_id);
+}
+
+/*
+ * Handle rmgr LOGICALMSG_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	SnapBuild  *builder = ctx->snapshot_builder;
+	XLogReaderState *r = buf->record;
+	TransactionId xid = XLogRecGetXid(r);
+	uint8		info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
+	RepOriginId origin_id = XLogRecGetOrigin(r);
+	Snapshot	snapshot;
+	xl_logical_message *message;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+		elog(ERROR, "unexpected RM_LOGICALMSG_ID record type: %u", info);
+
+	ReorderBufferProcessXid(ctx->reorder, XLogRecGetXid(r), buf->origptr);
+
+	/*
+	 * If we don't have snapshot or we are just fast-forwarding, there is no
+	 * point in decoding messages.
+	 */
+	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT ||
+		ctx->fast_forward)
+		return;
+
+	message = (xl_logical_message *) XLogRecGetData(r);
+
+	if (message->dbId != ctx->slot->data.database ||
+		FilterByOrigin(ctx, origin_id))
+		return;
+
+	if (message->transactional &&
+		!SnapBuildProcessChange(builder, xid, buf->origptr))
+		return;
+	else if (!message->transactional &&
+			 (SnapBuildCurrentState(builder) != SNAPBUILD_CONSISTENT ||
+			  SnapBuildXactNeedsSkip(builder, buf->origptr)))
+		return;
+
+	snapshot = SnapBuildGetOrBuildSnapshot(builder, xid);
+	ReorderBufferQueueMessage(ctx->reorder, xid, snapshot, buf->endptr,
+							  message->transactional,
+							  message->message, /* first part of message is
+												 * prefix */
+							  message->message_size,
+							  message->message + message->prefix_size);
+}
+
+/*
+ * Consolidated commit record handling between the different form of commit
+ * records.
+ *
+ * 'two_phase' indicates that caller wants to process the transaction in two
+ * phases, first process prepare if not already done and then process
+ * commit_prepared.
+ */
+static void
+DecodeCommit(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
+			 xl_xact_parsed_commit *parsed, TransactionId xid,
+			 bool two_phase)
+{
+	XLogRecPtr	origin_lsn = InvalidXLogRecPtr;
+	TimestampTz commit_time = parsed->xact_time;
+	RepOriginId origin_id = XLogRecGetOrigin(buf->record);
+	int			i;
+
+	if (parsed->xinfo & XACT_XINFO_HAS_ORIGIN)
+	{
+		origin_lsn = parsed->origin_lsn;
+		commit_time = parsed->origin_timestamp;
+	}
+
+	SnapBuildCommitTxn(ctx->snapshot_builder, buf->origptr, xid,
+					   parsed->nsubxacts, parsed->subxacts);
+
+	/* ----
+	 * Check whether we are interested in this specific transaction, and tell
+	 * the reorderbuffer to forget the content of the (sub-)transactions
+	 * if not.
+	 *
+	 * We can't just use ReorderBufferAbort() here, because we need to execute
+	 * the transaction's invalidations.  This currently won't be needed if
+	 * we're just skipping over the transaction because currently we only do
+	 * so during startup, to get to the first transaction the client needs. As
+	 * we have reset the catalog caches before starting to read WAL, and we
+	 * haven't yet touched any catalogs, there can't be anything to invalidate.
+	 * But if we're "forgetting" this commit because it happened in another
+	 * database, the invalidations might be important, because they could be
+	 * for shared catalogs and we might have loaded data into the relevant
+	 * syscaches.
+	 * ---
+	 */
+	if (DecodeTXNNeedSkip(ctx, buf, parsed->dbId, origin_id))
+	{
+		for (i = 0; i < parsed->nsubxacts; i++)
+		{
+			ReorderBufferForget(ctx->reorder, parsed->subxacts[i], buf->origptr);
+		}
+		ReorderBufferForget(ctx->reorder, xid, buf->origptr);
+
+		return;
+	}
+
+	/* tell the reorderbuffer about the surviving subtransactions */
+	for (i = 0; i < parsed->nsubxacts; i++)
+	{
+		ReorderBufferCommitChild(ctx->reorder, xid, parsed->subxacts[i],
+								 buf->origptr, buf->endptr);
+	}
+
+	/*
+	 * Send the final commit record if the transaction data is already
+	 * decoded, otherwise, process the entire transaction.
+	 */
+	if (two_phase)
+	{
+		ReorderBufferFinishPrepared(ctx->reorder, xid, buf->origptr, buf->endptr,
+									SnapBuildInitialConsistentPoint(ctx->snapshot_builder),
+									commit_time, origin_id, origin_lsn,
+									parsed->twophase_gid, true);
+	}
+	else
+	{
+		ReorderBufferCommit(ctx->reorder, xid, buf->origptr, buf->endptr,
+							commit_time, origin_id, origin_lsn);
+	}
+
+	/*
+	 * Update the decoding stats at transaction prepare/commit/abort.
+	 * Additionally we send the stats when we spill or stream the changes to
+	 * avoid losing them in case the decoding is interrupted. It is not clear
+	 * that sending more or less frequently than this would be better.
+	 */
+	UpdateDecodingStats(ctx);
+}
+
+/*
+ * Decode PREPARE record. Similar logic as in DecodeCommit.
+ *
+ * Note that we don't skip prepare even if have detected concurrent abort
+ * because it is quite possible that we had already sent some changes before we
+ * detect abort in which case we need to abort those changes in the subscriber.
+ * To abort such changes, we do send the prepare and then the rollback prepared
+ * which is what happened on the publisher-side as well. Now, we can invent a
+ * new abort API wherein in such cases we send abort and skip sending prepared
+ * and rollback prepared but then it is not that straightforward because we
+ * might have streamed this transaction by that time in which case it is
+ * handled when the rollback is encountered. It is not impossible to optimize
+ * the concurrent abort case but it can introduce design complexity w.r.t
+ * handling different cases so leaving it for now as it doesn't seem worth it.
+ */
+static void
+DecodePrepare(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
+			  xl_xact_parsed_prepare *parsed)
+{
+	SnapBuild  *builder = ctx->snapshot_builder;
+	XLogRecPtr	origin_lsn = parsed->origin_lsn;
+	TimestampTz prepare_time = parsed->xact_time;
+	XLogRecPtr	origin_id = XLogRecGetOrigin(buf->record);
+	int			i;
+	TransactionId xid = parsed->twophase_xid;
+
+	if (parsed->origin_timestamp != 0)
+		prepare_time = parsed->origin_timestamp;
+
+	/*
+	 * Remember the prepare info for a txn so that it can be used later in
+	 * commit prepared if required. See ReorderBufferFinishPrepared.
+	 */
+	if (!ReorderBufferRememberPrepareInfo(ctx->reorder, xid, buf->origptr,
+										  buf->endptr, prepare_time, origin_id,
+										  origin_lsn))
+		return;
+
+	/* We can't start streaming unless a consistent state is reached. */
+	if (SnapBuildCurrentState(builder) < SNAPBUILD_CONSISTENT)
+	{
+		ReorderBufferSkipPrepare(ctx->reorder, xid);
+		return;
+	}
+
+	/*
+	 * Check whether we need to process this transaction. See
+	 * DecodeTXNNeedSkip for the reasons why we sometimes want to skip the
+	 * transaction.
+	 *
+	 * We can't call ReorderBufferForget as we did in DecodeCommit as the txn
+	 * hasn't yet been committed, removing this txn before a commit might
+	 * result in the computation of an incorrect restart_lsn. See
+	 * SnapBuildProcessRunningXacts. But we need to process cache
+	 * invalidations if there are any for the reasons mentioned in
+	 * DecodeCommit.
+	 */
+	if (DecodeTXNNeedSkip(ctx, buf, parsed->dbId, origin_id))
+	{
+		ReorderBufferSkipPrepare(ctx->reorder, xid);
+		ReorderBufferInvalidate(ctx->reorder, xid, buf->origptr);
+		return;
+	}
+
+	/* Tell the reorderbuffer about the surviving subtransactions. */
+	for (i = 0; i < parsed->nsubxacts; i++)
+	{
+		ReorderBufferCommitChild(ctx->reorder, xid, parsed->subxacts[i],
+								 buf->origptr, buf->endptr);
+	}
+
+	/* replay actions of all transaction + subtransactions in order */
+	ReorderBufferPrepare(ctx->reorder, xid, parsed->twophase_gid);
+
+	/*
+	 * Update the decoding stats at transaction prepare/commit/abort.
+	 * Additionally we send the stats when we spill or stream the changes to
+	 * avoid losing them in case the decoding is interrupted. It is not clear
+	 * that sending more or less frequently than this would be better.
+	 */
+	UpdateDecodingStats(ctx);
+}
+
+
+/*
+ * Get the data from the various forms of abort records and pass it on to
+ * snapbuild.c and reorderbuffer.c.
+ *
+ * 'two_phase' indicates to finish prepared transaction.
+ */
+static void
+DecodeAbort(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
+			xl_xact_parsed_abort *parsed, TransactionId xid,
+			bool two_phase)
+{
+	int			i;
+	XLogRecPtr	origin_lsn = InvalidXLogRecPtr;
+	TimestampTz abort_time = parsed->xact_time;
+	XLogRecPtr	origin_id = XLogRecGetOrigin(buf->record);
+	bool		skip_xact;
+
+	if (parsed->xinfo & XACT_XINFO_HAS_ORIGIN)
+	{
+		origin_lsn = parsed->origin_lsn;
+		abort_time = parsed->origin_timestamp;
+	}
+
+	/*
+	 * Check whether we need to process this transaction. See
+	 * DecodeTXNNeedSkip for the reasons why we sometimes want to skip the
+	 * transaction.
+	 */
+	skip_xact = DecodeTXNNeedSkip(ctx, buf, parsed->dbId, origin_id);
+
+	/*
+	 * Send the final rollback record for a prepared transaction unless we
+	 * need to skip it. For non-two-phase xacts, simply forget the xact.
+	 */
+	if (two_phase && !skip_xact)
+	{
+		ReorderBufferFinishPrepared(ctx->reorder, xid, buf->origptr, buf->endptr,
+									InvalidXLogRecPtr,
+									abort_time, origin_id, origin_lsn,
+									parsed->twophase_gid, false);
+	}
+	else
+	{
+		for (i = 0; i < parsed->nsubxacts; i++)
+		{
+			ReorderBufferAbort(ctx->reorder, parsed->subxacts[i],
+							   buf->record->EndRecPtr);
+		}
+
+		ReorderBufferAbort(ctx->reorder, xid, buf->record->EndRecPtr);
+	}
+
+	/* update the decoding stats */
+	UpdateDecodingStats(ctx);
+}
+
+/*
+ * Parse XLOG_HEAP_INSERT (not MULTI_INSERT!) records into tuplebufs.
+ *
+ * Deletes can contain the new tuple.
+ */
+static void
+DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	Size		datalen;
+	char	   *tupledata;
+	Size		tuplelen;
+	XLogReaderState *r = buf->record;
+	xl_heap_insert *xlrec;
+	ReorderBufferChange *change;
+	RelFileNode target_node;
+
+	xlrec = (xl_heap_insert *) XLogRecGetData(r);
+
+	/*
+	 * Ignore insert records without new tuples (this does happen when
+	 * raw_heap_insert marks the TOAST record as HEAP_INSERT_NO_LOGICAL).
+	 */
+	if (!(xlrec->flags & XLH_INSERT_CONTAINS_NEW_TUPLE))
+		return;
+
+	/* only interested in our database */
+	XLogRecGetBlockTag(r, 0, &target_node, NULL, NULL);
+	if (target_node.dbNode != ctx->slot->data.database)
+		return;
+
+	/* output plugin doesn't look for this origin, no need to queue */
+	if (FilterByOrigin(ctx, XLogRecGetOrigin(r)))
+		return;
+
+	change = ReorderBufferGetChange(ctx->reorder);
+	if (!(xlrec->flags & XLH_INSERT_IS_SPECULATIVE))
+		change->action = REORDER_BUFFER_CHANGE_INSERT;
+	else
+		change->action = REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT;
+	change->origin_id = XLogRecGetOrigin(r);
+
+	memcpy(&change->data.tp.relnode, &target_node, sizeof(RelFileNode));
+
+	tupledata = XLogRecGetBlockData(r, 0, &datalen);
+	tuplelen = datalen - SizeOfHeapHeader;
+
+	change->data.tp.newtuple =
+		ReorderBufferGetTupleBuf(ctx->reorder, tuplelen);
+
+	DecodeXLogTuple(tupledata, datalen, change->data.tp.newtuple);
+
+	change->data.tp.clear_toast_afterwards = true;
+
+	ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r), buf->origptr,
+							 change,
+							 xlrec->flags & XLH_INSERT_ON_TOAST_RELATION);
+}
+
+/*
+ * Parse XLOG_HEAP_UPDATE and XLOG_HEAP_HOT_UPDATE, which have the same layout
+ * in the record, from wal into proper tuplebufs.
+ *
+ * Updates can possibly contain a new tuple and the old primary key.
+ */
+static void
+DecodeUpdate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	XLogReaderState *r = buf->record;
+	xl_heap_update *xlrec;
+	ReorderBufferChange *change;
+	char	   *data;
+	RelFileNode target_node;
+
+	xlrec = (xl_heap_update *) XLogRecGetData(r);
+
+	/* only interested in our database */
+	XLogRecGetBlockTag(r, 0, &target_node, NULL, NULL);
+	if (target_node.dbNode != ctx->slot->data.database)
+		return;
+
+	/* output plugin doesn't look for this origin, no need to queue */
+	if (FilterByOrigin(ctx, XLogRecGetOrigin(r)))
+		return;
+
+	change = ReorderBufferGetChange(ctx->reorder);
+	change->action = REORDER_BUFFER_CHANGE_UPDATE;
+	change->origin_id = XLogRecGetOrigin(r);
+	memcpy(&change->data.tp.relnode, &target_node, sizeof(RelFileNode));
+
+	if (xlrec->flags & XLH_UPDATE_CONTAINS_NEW_TUPLE)
+	{
+		Size		datalen;
+		Size		tuplelen;
+
+		data = XLogRecGetBlockData(r, 0, &datalen);
+
+		tuplelen = datalen - SizeOfHeapHeader;
+
+		change->data.tp.newtuple =
+			ReorderBufferGetTupleBuf(ctx->reorder, tuplelen);
+
+		DecodeXLogTuple(data, datalen, change->data.tp.newtuple);
+	}
+
+	if (xlrec->flags & XLH_UPDATE_CONTAINS_OLD)
+	{
+		Size		datalen;
+		Size		tuplelen;
+
+		/* caution, remaining data in record is not aligned */
+		data = XLogRecGetData(r) + SizeOfHeapUpdate;
+		datalen = XLogRecGetDataLen(r) - SizeOfHeapUpdate;
+		tuplelen = datalen - SizeOfHeapHeader;
+
+		change->data.tp.oldtuple =
+			ReorderBufferGetTupleBuf(ctx->reorder, tuplelen);
+
+		DecodeXLogTuple(data, datalen, change->data.tp.oldtuple);
+	}
+
+	change->data.tp.clear_toast_afterwards = true;
+
+	ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r), buf->origptr,
+							 change, false);
+}
+
+/*
+ * Parse XLOG_HEAP_DELETE from wal into proper tuplebufs.
+ *
+ * Deletes can possibly contain the old primary key.
+ */
+static void
+DecodeDelete(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	XLogReaderState *r = buf->record;
+	xl_heap_delete *xlrec;
+	ReorderBufferChange *change;
+	RelFileNode target_node;
+
+	xlrec = (xl_heap_delete *) XLogRecGetData(r);
+
+	/* only interested in our database */
+	XLogRecGetBlockTag(r, 0, &target_node, NULL, NULL);
+	if (target_node.dbNode != ctx->slot->data.database)
+		return;
+
+	/* output plugin doesn't look for this origin, no need to queue */
+	if (FilterByOrigin(ctx, XLogRecGetOrigin(r)))
+		return;
+
+	change = ReorderBufferGetChange(ctx->reorder);
+
+	if (xlrec->flags & XLH_DELETE_IS_SUPER)
+		change->action = REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT;
+	else
+		change->action = REORDER_BUFFER_CHANGE_DELETE;
+
+	change->origin_id = XLogRecGetOrigin(r);
+
+	memcpy(&change->data.tp.relnode, &target_node, sizeof(RelFileNode));
+
+	/* old primary key stored */
+	if (xlrec->flags & XLH_DELETE_CONTAINS_OLD)
+	{
+		Size		datalen = XLogRecGetDataLen(r) - SizeOfHeapDelete;
+		Size		tuplelen = datalen - SizeOfHeapHeader;
+
+		Assert(XLogRecGetDataLen(r) > (SizeOfHeapDelete + SizeOfHeapHeader));
+
+		change->data.tp.oldtuple =
+			ReorderBufferGetTupleBuf(ctx->reorder, tuplelen);
+
+		DecodeXLogTuple((char *) xlrec + SizeOfHeapDelete,
+						datalen, change->data.tp.oldtuple);
+	}
+
+	change->data.tp.clear_toast_afterwards = true;
+
+	ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r), buf->origptr,
+							 change, false);
+}
+
+/*
+ * Parse XLOG_HEAP_TRUNCATE from wal
+ */
+static void
+DecodeTruncate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	XLogReaderState *r = buf->record;
+	xl_heap_truncate *xlrec;
+	ReorderBufferChange *change;
+
+	xlrec = (xl_heap_truncate *) XLogRecGetData(r);
+
+	/* only interested in our database */
+	if (xlrec->dbId != ctx->slot->data.database)
+		return;
+
+	/* output plugin doesn't look for this origin, no need to queue */
+	if (FilterByOrigin(ctx, XLogRecGetOrigin(r)))
+		return;
+
+	change = ReorderBufferGetChange(ctx->reorder);
+	change->action = REORDER_BUFFER_CHANGE_TRUNCATE;
+	change->origin_id = XLogRecGetOrigin(r);
+	if (xlrec->flags & XLH_TRUNCATE_CASCADE)
+		change->data.truncate.cascade = true;
+	if (xlrec->flags & XLH_TRUNCATE_RESTART_SEQS)
+		change->data.truncate.restart_seqs = true;
+	change->data.truncate.nrelids = xlrec->nrelids;
+	change->data.truncate.relids = ReorderBufferGetRelids(ctx->reorder,
+														  xlrec->nrelids);
+	memcpy(change->data.truncate.relids, xlrec->relids,
+		   xlrec->nrelids * sizeof(Oid));
+	ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r),
+							 buf->origptr, change, false);
+}
+
+/*
+ * Decode XLOG_HEAP2_MULTI_INSERT_insert record into multiple tuplebufs.
+ *
+ * Currently MULTI_INSERT will always contain the full tuples.
+ */
+static void
+DecodeMultiInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	XLogReaderState *r = buf->record;
+	xl_heap_multi_insert *xlrec;
+	int			i;
+	char	   *data;
+	char	   *tupledata;
+	Size		tuplelen;
+	RelFileNode rnode;
+
+	xlrec = (xl_heap_multi_insert *) XLogRecGetData(r);
+
+	/*
+	 * Ignore insert records without new tuples.  This happens when a
+	 * multi_insert is done on a catalog or on a non-persistent relation.
+	 */
+	if (!(xlrec->flags & XLH_INSERT_CONTAINS_NEW_TUPLE))
+		return;
+
+	/* only interested in our database */
+	XLogRecGetBlockTag(r, 0, &rnode, NULL, NULL);
+	if (rnode.dbNode != ctx->slot->data.database)
+		return;
+
+	/* output plugin doesn't look for this origin, no need to queue */
+	if (FilterByOrigin(ctx, XLogRecGetOrigin(r)))
+		return;
+
+	/*
+	 * We know that this multi_insert isn't for a catalog, so the block should
+	 * always have data even if a full-page write of it is taken.
+	 */
+	tupledata = XLogRecGetBlockData(r, 0, &tuplelen);
+	Assert(tupledata != NULL);
+
+	data = tupledata;
+	for (i = 0; i < xlrec->ntuples; i++)
+	{
+		ReorderBufferChange *change;
+		xl_multi_insert_tuple *xlhdr;
+		int			datalen;
+		ReorderBufferTupleBuf *tuple;
+		HeapTupleHeader header;
+
+		change = ReorderBufferGetChange(ctx->reorder);
+		change->action = REORDER_BUFFER_CHANGE_INSERT;
+		change->origin_id = XLogRecGetOrigin(r);
+
+		memcpy(&change->data.tp.relnode, &rnode, sizeof(RelFileNode));
+
+		xlhdr = (xl_multi_insert_tuple *) SHORTALIGN(data);
+		data = ((char *) xlhdr) + SizeOfMultiInsertTuple;
+		datalen = xlhdr->datalen;
+
+		change->data.tp.newtuple =
+			ReorderBufferGetTupleBuf(ctx->reorder, datalen);
+
+		tuple = change->data.tp.newtuple;
+		header = tuple->tuple.t_data;
+
+		/* not a disk based tuple */
+		ItemPointerSetInvalid(&tuple->tuple.t_self);
+
+		/*
+		 * We can only figure this out after reassembling the transactions.
+		 */
+		tuple->tuple.t_tableOid = InvalidOid;
+
+		tuple->tuple.t_len = datalen + SizeofHeapTupleHeader;
+
+		memset(header, 0, SizeofHeapTupleHeader);
+
+		memcpy((char *) tuple->tuple.t_data + SizeofHeapTupleHeader,
+			   (char *) data,
+			   datalen);
+		header->t_infomask = xlhdr->t_infomask;
+		header->t_infomask2 = xlhdr->t_infomask2;
+		header->t_hoff = xlhdr->t_hoff;
+
+		/*
+		 * Reset toast reassembly state only after the last row in the last
+		 * xl_multi_insert_tuple record emitted by one heap_multi_insert()
+		 * call.
+		 */
+		if (xlrec->flags & XLH_INSERT_LAST_IN_MULTI &&
+			(i + 1) == xlrec->ntuples)
+			change->data.tp.clear_toast_afterwards = true;
+		else
+			change->data.tp.clear_toast_afterwards = false;
+
+		ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r),
+								 buf->origptr, change, false);
+
+		/* move to the next xl_multi_insert_tuple entry */
+		data += datalen;
+	}
+	Assert(data == tupledata + tuplelen);
+}
+
+/*
+ * Parse XLOG_HEAP_CONFIRM from wal into a confirmation change.
+ *
+ * This is pretty trivial, all the state essentially already setup by the
+ * speculative insertion.
+ */
+static void
+DecodeSpecConfirm(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	XLogReaderState *r = buf->record;
+	ReorderBufferChange *change;
+	RelFileNode target_node;
+
+	/* only interested in our database */
+	XLogRecGetBlockTag(r, 0, &target_node, NULL, NULL);
+	if (target_node.dbNode != ctx->slot->data.database)
+		return;
+
+	/* output plugin doesn't look for this origin, no need to queue */
+	if (FilterByOrigin(ctx, XLogRecGetOrigin(r)))
+		return;
+
+	change = ReorderBufferGetChange(ctx->reorder);
+	change->action = REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM;
+	change->origin_id = XLogRecGetOrigin(r);
+
+	memcpy(&change->data.tp.relnode, &target_node, sizeof(RelFileNode));
+
+	change->data.tp.clear_toast_afterwards = true;
+
+	ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r), buf->origptr,
+							 change, false);
+}
+
+
+/*
+ * Read a HeapTuple as WAL logged by heap_insert, heap_update and heap_delete
+ * (but not by heap_multi_insert) into a tuplebuf.
+ *
+ * The size 'len' and the pointer 'data' in the record need to be
+ * computed outside as they are record specific.
+ */
+static void
+DecodeXLogTuple(char *data, Size len, ReorderBufferTupleBuf *tuple)
+{
+	xl_heap_header xlhdr;
+	int			datalen = len - SizeOfHeapHeader;
+	HeapTupleHeader header;
+
+	Assert(datalen >= 0);
+
+	tuple->tuple.t_len = datalen + SizeofHeapTupleHeader;
+	header = tuple->tuple.t_data;
+
+	/* not a disk based tuple */
+	ItemPointerSetInvalid(&tuple->tuple.t_self);
+
+	/* we can only figure this out after reassembling the transactions */
+	tuple->tuple.t_tableOid = InvalidOid;
+
+	/* data is not stored aligned, copy to aligned storage */
+	memcpy((char *) &xlhdr,
+		   data,
+		   SizeOfHeapHeader);
+
+	memset(header, 0, SizeofHeapTupleHeader);
+
+	memcpy(((char *) tuple->tuple.t_data) + SizeofHeapTupleHeader,
+		   data + SizeOfHeapHeader,
+		   datalen);
+
+	header->t_infomask = xlhdr.t_infomask;
+	header->t_infomask2 = xlhdr.t_infomask2;
+	header->t_hoff = xlhdr.t_hoff;
+}
+
+/*
+ * Check whether we are interested in this specific transaction.
+ *
+ * There can be several reasons we might not be interested in this
+ * transaction:
+ * 1) We might not be interested in decoding transactions up to this
+ *	  LSN. This can happen because we previously decoded it and now just
+ *	  are restarting or if we haven't assembled a consistent snapshot yet.
+ * 2) The transaction happened in another database.
+ * 3) The output plugin is not interested in the origin.
+ * 4) We are doing fast-forwarding
+ */
+static bool
+DecodeTXNNeedSkip(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
+				  Oid txn_dbid, RepOriginId origin_id)
+{
+	return (SnapBuildXactNeedsSkip(ctx->snapshot_builder, buf->origptr) ||
+			(txn_dbid != InvalidOid && txn_dbid != ctx->slot->data.database) ||
+			ctx->fast_forward || FilterByOrigin(ctx, origin_id));
+}
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
new file mode 100644
index 0000000..3c69817
--- /dev/null
+++ b/src/backend/replication/logical/launcher.c
@@ -0,0 +1,1024 @@
+/*-------------------------------------------------------------------------
+ * launcher.c
+ *	   PostgreSQL logical replication worker launcher process
+ *
+ * Copyright (c) 2016-2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/launcher.c
+ *
+ * NOTES
+ *	  This module contains the logical replication worker launcher which
+ *	  uses the background worker infrastructure to start the logical
+ *	  replication workers for every enabled subscription.
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/heapam.h"
+#include "access/htup.h"
+#include "access/htup_details.h"
+#include "access/tableam.h"
+#include "access/xact.h"
+#include "catalog/pg_subscription.h"
+#include "catalog/pg_subscription_rel.h"
+#include "funcapi.h"
+#include "libpq/pqsignal.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "postmaster/bgworker.h"
+#include "postmaster/fork_process.h"
+#include "postmaster/interrupt.h"
+#include "postmaster/postmaster.h"
+#include "replication/logicallauncher.h"
+#include "replication/logicalworker.h"
+#include "replication/slot.h"
+#include "replication/walreceiver.h"
+#include "replication/worker_internal.h"
+#include "storage/ipc.h"
+#include "storage/proc.h"
+#include "storage/procarray.h"
+#include "storage/procsignal.h"
+#include "tcop/tcopprot.h"
+#include "utils/memutils.h"
+#include "utils/pg_lsn.h"
+#include "utils/ps_status.h"
+#include "utils/snapmgr.h"
+#include "utils/timeout.h"
+
+/* max sleep time between cycles (3min) */
+#define DEFAULT_NAPTIME_PER_CYCLE 180000L
+
+int			max_logical_replication_workers = 4;
+int			max_sync_workers_per_subscription = 2;
+
+LogicalRepWorker *MyLogicalRepWorker = NULL;
+
+typedef struct LogicalRepCtxStruct
+{
+	/* Supervisor process. */
+	pid_t		launcher_pid;
+
+	/* Background workers. */
+	LogicalRepWorker workers[FLEXIBLE_ARRAY_MEMBER];
+} LogicalRepCtxStruct;
+
+LogicalRepCtxStruct *LogicalRepCtx;
+
+static void ApplyLauncherWakeup(void);
+static void logicalrep_launcher_onexit(int code, Datum arg);
+static void logicalrep_worker_onexit(int code, Datum arg);
+static void logicalrep_worker_detach(void);
+static void logicalrep_worker_cleanup(LogicalRepWorker *worker);
+
+static bool on_commit_launcher_wakeup = false;
+
+Datum		pg_stat_get_subscription(PG_FUNCTION_ARGS);
+
+
+/*
+ * Load the list of subscriptions.
+ *
+ * Only the fields interesting for worker start/stop functions are filled for
+ * each subscription.
+ */
+static List *
+get_subscription_list(void)
+{
+	List	   *res = NIL;
+	Relation	rel;
+	TableScanDesc scan;
+	HeapTuple	tup;
+	MemoryContext resultcxt;
+
+	/* This is the context that we will allocate our output data in */
+	resultcxt = CurrentMemoryContext;
+
+	/*
+	 * Start a transaction so we can access pg_database, and get a snapshot.
+	 * We don't have a use for the snapshot itself, but we're interested in
+	 * the secondary effect that it sets RecentGlobalXmin.  (This is critical
+	 * for anything that reads heap pages, because HOT may decide to prune
+	 * them even if the process doesn't attempt to modify any tuples.)
+	 *
+	 * FIXME: This comment is inaccurate / the code buggy. A snapshot that is
+	 * not pushed/active does not reliably prevent HOT pruning (->xmin could
+	 * e.g. be cleared when cache invalidations are processed).
+	 */
+	StartTransactionCommand();
+	(void) GetTransactionSnapshot();
+
+	rel = table_open(SubscriptionRelationId, AccessShareLock);
+	scan = table_beginscan_catalog(rel, 0, NULL);
+
+	while (HeapTupleIsValid(tup = heap_getnext(scan, ForwardScanDirection)))
+	{
+		Form_pg_subscription subform = (Form_pg_subscription) GETSTRUCT(tup);
+		Subscription *sub;
+		MemoryContext oldcxt;
+
+		/*
+		 * Allocate our results in the caller's context, not the
+		 * transaction's. We do this inside the loop, and restore the original
+		 * context at the end, so that leaky things like heap_getnext() are
+		 * not called in a potentially long-lived context.
+		 */
+		oldcxt = MemoryContextSwitchTo(resultcxt);
+
+		sub = (Subscription *) palloc0(sizeof(Subscription));
+		sub->oid = subform->oid;
+		sub->dbid = subform->subdbid;
+		sub->owner = subform->subowner;
+		sub->enabled = subform->subenabled;
+		sub->name = pstrdup(NameStr(subform->subname));
+		/* We don't fill fields we are not interested in. */
+
+		res = lappend(res, sub);
+		MemoryContextSwitchTo(oldcxt);
+	}
+
+	table_endscan(scan);
+	table_close(rel, AccessShareLock);
+
+	CommitTransactionCommand();
+
+	return res;
+}
+
+/*
+ * Wait for a background worker to start up and attach to the shmem context.
+ *
+ * This is only needed for cleaning up the shared memory in case the worker
+ * fails to attach.
+ */
+static void
+WaitForReplicationWorkerAttach(LogicalRepWorker *worker,
+							   uint16 generation,
+							   BackgroundWorkerHandle *handle)
+{
+	BgwHandleStatus status;
+	int			rc;
+
+	for (;;)
+	{
+		pid_t		pid;
+
+		CHECK_FOR_INTERRUPTS();
+
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
+		/* Worker either died or has started; no need to do anything. */
+		if (!worker->in_use || worker->proc)
+		{
+			LWLockRelease(LogicalRepWorkerLock);
+			return;
+		}
+
+		LWLockRelease(LogicalRepWorkerLock);
+
+		/* Check if worker has died before attaching, and clean up after it. */
+		status = GetBackgroundWorkerPid(handle, &pid);
+
+		if (status == BGWH_STOPPED)
+		{
+			LWLockAcquire(LogicalRepWorkerLock, LW_EXCLUSIVE);
+			/* Ensure that this was indeed the worker we waited for. */
+			if (generation == worker->generation)
+				logicalrep_worker_cleanup(worker);
+			LWLockRelease(LogicalRepWorkerLock);
+			return;
+		}
+
+		/*
+		 * We need timeout because we generally don't get notified via latch
+		 * about the worker attach.  But we don't expect to have to wait long.
+		 */
+		rc = WaitLatch(MyLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+					   10L, WAIT_EVENT_BGWORKER_STARTUP);
+
+		if (rc & WL_LATCH_SET)
+		{
+			ResetLatch(MyLatch);
+			CHECK_FOR_INTERRUPTS();
+		}
+	}
+}
+
+/*
+ * Walks the workers array and searches for one that matches given
+ * subscription id and relid.
+ */
+LogicalRepWorker *
+logicalrep_worker_find(Oid subid, Oid relid, bool only_running)
+{
+	int			i;
+	LogicalRepWorker *res = NULL;
+
+	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
+
+	/* Search for attached worker for a given subscription id. */
+	for (i = 0; i < max_logical_replication_workers; i++)
+	{
+		LogicalRepWorker *w = &LogicalRepCtx->workers[i];
+
+		if (w->in_use && w->subid == subid && w->relid == relid &&
+			(!only_running || w->proc))
+		{
+			res = w;
+			break;
+		}
+	}
+
+	return res;
+}
+
+/*
+ * Similar to logicalrep_worker_find(), but returns list of all workers for
+ * the subscription, instead just one.
+ */
+List *
+logicalrep_workers_find(Oid subid, bool only_running)
+{
+	int			i;
+	List	   *res = NIL;
+
+	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
+
+	/* Search for attached worker for a given subscription id. */
+	for (i = 0; i < max_logical_replication_workers; i++)
+	{
+		LogicalRepWorker *w = &LogicalRepCtx->workers[i];
+
+		if (w->in_use && w->subid == subid && (!only_running || w->proc))
+			res = lappend(res, w);
+	}
+
+	return res;
+}
+
+/*
+ * Start new apply background worker, if possible.
+ */
+void
+logicalrep_worker_launch(Oid dbid, Oid subid, const char *subname, Oid userid,
+						 Oid relid)
+{
+	BackgroundWorker bgw;
+	BackgroundWorkerHandle *bgw_handle;
+	uint16		generation;
+	int			i;
+	int			slot = 0;
+	LogicalRepWorker *worker = NULL;
+	int			nsyncworkers;
+	TimestampTz now;
+
+	ereport(DEBUG1,
+			(errmsg_internal("starting logical replication worker for subscription \"%s\"",
+							 subname)));
+
+	/* Report this after the initial starting message for consistency. */
+	if (max_replication_slots == 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
+				 errmsg("cannot start logical replication workers when max_replication_slots = 0")));
+
+	/*
+	 * We need to do the modification of the shared memory under lock so that
+	 * we have consistent view.
+	 */
+	LWLockAcquire(LogicalRepWorkerLock, LW_EXCLUSIVE);
+
+retry:
+	/* Find unused worker slot. */
+	for (i = 0; i < max_logical_replication_workers; i++)
+	{
+		LogicalRepWorker *w = &LogicalRepCtx->workers[i];
+
+		if (!w->in_use)
+		{
+			worker = w;
+			slot = i;
+			break;
+		}
+	}
+
+	nsyncworkers = logicalrep_sync_worker_count(subid);
+
+	now = GetCurrentTimestamp();
+
+	/*
+	 * If we didn't find a free slot, try to do garbage collection.  The
+	 * reason we do this is because if some worker failed to start up and its
+	 * parent has crashed while waiting, the in_use state was never cleared.
+	 */
+	if (worker == NULL || nsyncworkers >= max_sync_workers_per_subscription)
+	{
+		bool		did_cleanup = false;
+
+		for (i = 0; i < max_logical_replication_workers; i++)
+		{
+			LogicalRepWorker *w = &LogicalRepCtx->workers[i];
+
+			/*
+			 * If the worker was marked in use but didn't manage to attach in
+			 * time, clean it up.
+			 */
+			if (w->in_use && !w->proc &&
+				TimestampDifferenceExceeds(w->launch_time, now,
+										   wal_receiver_timeout))
+			{
+				elog(WARNING,
+					 "logical replication worker for subscription %u took too long to start; canceled",
+					 w->subid);
+
+				logicalrep_worker_cleanup(w);
+				did_cleanup = true;
+			}
+		}
+
+		if (did_cleanup)
+			goto retry;
+	}
+
+	/*
+	 * We don't allow to invoke more sync workers once we have reached the sync
+	 * worker limit per subscription. So, just return silently as we might get
+	 * here because of an otherwise harmless race condition.
+	 */
+	if (OidIsValid(relid) && nsyncworkers >= max_sync_workers_per_subscription)
+	{
+		LWLockRelease(LogicalRepWorkerLock);
+		return;
+	}
+
+	/*
+	 * However if there are no more free worker slots, inform user about it
+	 * before exiting.
+	 */
+	if (worker == NULL)
+	{
+		LWLockRelease(LogicalRepWorkerLock);
+		ereport(WARNING,
+				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
+				 errmsg("out of logical replication worker slots"),
+				 errhint("You might need to increase max_logical_replication_workers.")));
+		return;
+	}
+
+	/* Prepare the worker slot. */
+	worker->launch_time = now;
+	worker->in_use = true;
+	worker->generation++;
+	worker->proc = NULL;
+	worker->dbid = dbid;
+	worker->userid = userid;
+	worker->subid = subid;
+	worker->relid = relid;
+	worker->relstate = SUBREL_STATE_UNKNOWN;
+	worker->relstate_lsn = InvalidXLogRecPtr;
+	worker->last_lsn = InvalidXLogRecPtr;
+	TIMESTAMP_NOBEGIN(worker->last_send_time);
+	TIMESTAMP_NOBEGIN(worker->last_recv_time);
+	worker->reply_lsn = InvalidXLogRecPtr;
+	TIMESTAMP_NOBEGIN(worker->reply_time);
+
+	/* Before releasing lock, remember generation for future identification. */
+	generation = worker->generation;
+
+	LWLockRelease(LogicalRepWorkerLock);
+
+	/* Register the new dynamic worker. */
+	memset(&bgw, 0, sizeof(bgw));
+	bgw.bgw_flags = BGWORKER_SHMEM_ACCESS |
+		BGWORKER_BACKEND_DATABASE_CONNECTION;
+	bgw.bgw_start_time = BgWorkerStart_RecoveryFinished;
+	snprintf(bgw.bgw_library_name, BGW_MAXLEN, "postgres");
+	snprintf(bgw.bgw_function_name, BGW_MAXLEN, "ApplyWorkerMain");
+	if (OidIsValid(relid))
+		snprintf(bgw.bgw_name, BGW_MAXLEN,
+				 "logical replication worker for subscription %u sync %u", subid, relid);
+	else
+		snprintf(bgw.bgw_name, BGW_MAXLEN,
+				 "logical replication worker for subscription %u", subid);
+	snprintf(bgw.bgw_type, BGW_MAXLEN, "logical replication worker");
+
+	bgw.bgw_restart_time = BGW_NEVER_RESTART;
+	bgw.bgw_notify_pid = MyProcPid;
+	bgw.bgw_main_arg = Int32GetDatum(slot);
+
+	if (!RegisterDynamicBackgroundWorker(&bgw, &bgw_handle))
+	{
+		/* Failed to start worker, so clean up the worker slot. */
+		LWLockAcquire(LogicalRepWorkerLock, LW_EXCLUSIVE);
+		Assert(generation == worker->generation);
+		logicalrep_worker_cleanup(worker);
+		LWLockRelease(LogicalRepWorkerLock);
+
+		ereport(WARNING,
+				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
+				 errmsg("out of background worker slots"),
+				 errhint("You might need to increase max_worker_processes.")));
+		return;
+	}
+
+	/* Now wait until it attaches. */
+	WaitForReplicationWorkerAttach(worker, generation, bgw_handle);
+}
+
+/*
+ * Stop the logical replication worker for subid/relid, if any, and wait until
+ * it detaches from the slot.
+ */
+void
+logicalrep_worker_stop(Oid subid, Oid relid)
+{
+	LogicalRepWorker *worker;
+	uint16		generation;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
+	worker = logicalrep_worker_find(subid, relid, false);
+
+	/* No worker, nothing to do. */
+	if (!worker)
+	{
+		LWLockRelease(LogicalRepWorkerLock);
+		return;
+	}
+
+	/*
+	 * Remember which generation was our worker so we can check if what we see
+	 * is still the same one.
+	 */
+	generation = worker->generation;
+
+	/*
+	 * If we found a worker but it does not have proc set then it is still
+	 * starting up; wait for it to finish starting and then kill it.
+	 */
+	while (worker->in_use && !worker->proc)
+	{
+		int			rc;
+
+		LWLockRelease(LogicalRepWorkerLock);
+
+		/* Wait a bit --- we don't expect to have to wait long. */
+		rc = WaitLatch(MyLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+					   10L, WAIT_EVENT_BGWORKER_STARTUP);
+
+		if (rc & WL_LATCH_SET)
+		{
+			ResetLatch(MyLatch);
+			CHECK_FOR_INTERRUPTS();
+		}
+
+		/* Recheck worker status. */
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
+		/*
+		 * Check whether the worker slot is no longer used, which would mean
+		 * that the worker has exited, or whether the worker generation is
+		 * different, meaning that a different worker has taken the slot.
+		 */
+		if (!worker->in_use || worker->generation != generation)
+		{
+			LWLockRelease(LogicalRepWorkerLock);
+			return;
+		}
+
+		/* Worker has assigned proc, so it has started. */
+		if (worker->proc)
+			break;
+	}
+
+	/* Now terminate the worker ... */
+	kill(worker->proc->pid, SIGTERM);
+
+	/* ... and wait for it to die. */
+	for (;;)
+	{
+		int			rc;
+
+		/* is it gone? */
+		if (!worker->proc || worker->generation != generation)
+			break;
+
+		LWLockRelease(LogicalRepWorkerLock);
+
+		/* Wait a bit --- we don't expect to have to wait long. */
+		rc = WaitLatch(MyLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+					   10L, WAIT_EVENT_BGWORKER_SHUTDOWN);
+
+		if (rc & WL_LATCH_SET)
+		{
+			ResetLatch(MyLatch);
+			CHECK_FOR_INTERRUPTS();
+		}
+
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	}
+
+	LWLockRelease(LogicalRepWorkerLock);
+}
+
+/*
+ * Wake up (using latch) any logical replication worker for specified sub/rel.
+ */
+void
+logicalrep_worker_wakeup(Oid subid, Oid relid)
+{
+	LogicalRepWorker *worker;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
+	worker = logicalrep_worker_find(subid, relid, true);
+
+	if (worker)
+		logicalrep_worker_wakeup_ptr(worker);
+
+	LWLockRelease(LogicalRepWorkerLock);
+}
+
+/*
+ * Wake up (using latch) the specified logical replication worker.
+ *
+ * Caller must hold lock, else worker->proc could change under us.
+ */
+void
+logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker)
+{
+	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
+
+	SetLatch(&worker->proc->procLatch);
+}
+
+/*
+ * Attach to a slot.
+ */
+void
+logicalrep_worker_attach(int slot)
+{
+	/* Block concurrent access. */
+	LWLockAcquire(LogicalRepWorkerLock, LW_EXCLUSIVE);
+
+	Assert(slot >= 0 && slot < max_logical_replication_workers);
+	MyLogicalRepWorker = &LogicalRepCtx->workers[slot];
+
+	if (!MyLogicalRepWorker->in_use)
+	{
+		LWLockRelease(LogicalRepWorkerLock);
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("logical replication worker slot %d is empty, cannot attach",
+						slot)));
+	}
+
+	if (MyLogicalRepWorker->proc)
+	{
+		LWLockRelease(LogicalRepWorkerLock);
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("logical replication worker slot %d is already used by "
+						"another worker, cannot attach", slot)));
+	}
+
+	MyLogicalRepWorker->proc = MyProc;
+	before_shmem_exit(logicalrep_worker_onexit, (Datum) 0);
+
+	LWLockRelease(LogicalRepWorkerLock);
+}
+
+/*
+ * Detach the worker (cleans up the worker info).
+ */
+static void
+logicalrep_worker_detach(void)
+{
+	/* Block concurrent access. */
+	LWLockAcquire(LogicalRepWorkerLock, LW_EXCLUSIVE);
+
+	logicalrep_worker_cleanup(MyLogicalRepWorker);
+
+	LWLockRelease(LogicalRepWorkerLock);
+}
+
+/*
+ * Clean up worker info.
+ */
+static void
+logicalrep_worker_cleanup(LogicalRepWorker *worker)
+{
+	Assert(LWLockHeldByMeInMode(LogicalRepWorkerLock, LW_EXCLUSIVE));
+
+	worker->in_use = false;
+	worker->proc = NULL;
+	worker->dbid = InvalidOid;
+	worker->userid = InvalidOid;
+	worker->subid = InvalidOid;
+	worker->relid = InvalidOid;
+}
+
+/*
+ * Cleanup function for logical replication launcher.
+ *
+ * Called on logical replication launcher exit.
+ */
+static void
+logicalrep_launcher_onexit(int code, Datum arg)
+{
+	LogicalRepCtx->launcher_pid = 0;
+}
+
+/*
+ * Cleanup function.
+ *
+ * Called on logical replication worker exit.
+ */
+static void
+logicalrep_worker_onexit(int code, Datum arg)
+{
+	/* Disconnect gracefully from the remote side. */
+	if (LogRepWorkerWalRcvConn)
+		walrcv_disconnect(LogRepWorkerWalRcvConn);
+
+	logicalrep_worker_detach();
+
+	ApplyLauncherWakeup();
+}
+
+/*
+ * Count the number of registered (not necessarily running) sync workers
+ * for a subscription.
+ */
+int
+logicalrep_sync_worker_count(Oid subid)
+{
+	int			i;
+	int			res = 0;
+
+	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
+
+	/* Search for attached worker for a given subscription id. */
+	for (i = 0; i < max_logical_replication_workers; i++)
+	{
+		LogicalRepWorker *w = &LogicalRepCtx->workers[i];
+
+		if (w->subid == subid && OidIsValid(w->relid))
+			res++;
+	}
+
+	return res;
+}
+
+/*
+ * ApplyLauncherShmemSize
+ *		Compute space needed for replication launcher shared memory
+ */
+Size
+ApplyLauncherShmemSize(void)
+{
+	Size		size;
+
+	/*
+	 * Need the fixed struct and the array of LogicalRepWorker.
+	 */
+	size = sizeof(LogicalRepCtxStruct);
+	size = MAXALIGN(size);
+	size = add_size(size, mul_size(max_logical_replication_workers,
+								   sizeof(LogicalRepWorker)));
+	return size;
+}
+
+/*
+ * ApplyLauncherRegister
+ *		Register a background worker running the logical replication launcher.
+ */
+void
+ApplyLauncherRegister(void)
+{
+	BackgroundWorker bgw;
+
+	if (max_logical_replication_workers == 0)
+		return;
+
+	memset(&bgw, 0, sizeof(bgw));
+	bgw.bgw_flags = BGWORKER_SHMEM_ACCESS |
+		BGWORKER_BACKEND_DATABASE_CONNECTION;
+	bgw.bgw_start_time = BgWorkerStart_RecoveryFinished;
+	snprintf(bgw.bgw_library_name, BGW_MAXLEN, "postgres");
+	snprintf(bgw.bgw_function_name, BGW_MAXLEN, "ApplyLauncherMain");
+	snprintf(bgw.bgw_name, BGW_MAXLEN,
+			 "logical replication launcher");
+	snprintf(bgw.bgw_type, BGW_MAXLEN,
+			 "logical replication launcher");
+	bgw.bgw_restart_time = 5;
+	bgw.bgw_notify_pid = 0;
+	bgw.bgw_main_arg = (Datum) 0;
+
+	RegisterBackgroundWorker(&bgw);
+}
+
+/*
+ * ApplyLauncherShmemInit
+ *		Allocate and initialize replication launcher shared memory
+ */
+void
+ApplyLauncherShmemInit(void)
+{
+	bool		found;
+
+	LogicalRepCtx = (LogicalRepCtxStruct *)
+		ShmemInitStruct("Logical Replication Launcher Data",
+						ApplyLauncherShmemSize(),
+						&found);
+
+	if (!found)
+	{
+		int			slot;
+
+		memset(LogicalRepCtx, 0, ApplyLauncherShmemSize());
+
+		/* Initialize memory and spin locks for each worker slot. */
+		for (slot = 0; slot < max_logical_replication_workers; slot++)
+		{
+			LogicalRepWorker *worker = &LogicalRepCtx->workers[slot];
+
+			memset(worker, 0, sizeof(LogicalRepWorker));
+			SpinLockInit(&worker->relmutex);
+		}
+	}
+}
+
+/*
+ * Wakeup the launcher on commit if requested.
+ */
+void
+AtEOXact_ApplyLauncher(bool isCommit)
+{
+	if (isCommit)
+	{
+		if (on_commit_launcher_wakeup)
+			ApplyLauncherWakeup();
+	}
+
+	on_commit_launcher_wakeup = false;
+}
+
+/*
+ * Request wakeup of the launcher on commit of the transaction.
+ *
+ * This is used to send launcher signal to stop sleeping and process the
+ * subscriptions when current transaction commits. Should be used when new
+ * tuple was added to the pg_subscription catalog.
+*/
+void
+ApplyLauncherWakeupAtCommit(void)
+{
+	if (!on_commit_launcher_wakeup)
+		on_commit_launcher_wakeup = true;
+}
+
+static void
+ApplyLauncherWakeup(void)
+{
+	if (LogicalRepCtx->launcher_pid != 0)
+		kill(LogicalRepCtx->launcher_pid, SIGUSR1);
+}
+
+/*
+ * Main loop for the apply launcher process.
+ */
+void
+ApplyLauncherMain(Datum main_arg)
+{
+	TimestampTz last_start_time = 0;
+
+	ereport(DEBUG1,
+			(errmsg_internal("logical replication launcher started")));
+
+	before_shmem_exit(logicalrep_launcher_onexit, (Datum) 0);
+
+	Assert(LogicalRepCtx->launcher_pid == 0);
+	LogicalRepCtx->launcher_pid = MyProcPid;
+
+	/* Establish signal handlers. */
+	pqsignal(SIGHUP, SignalHandlerForConfigReload);
+	pqsignal(SIGTERM, die);
+	BackgroundWorkerUnblockSignals();
+
+	/*
+	 * Establish connection to nailed catalogs (we only ever access
+	 * pg_subscription).
+	 */
+	BackgroundWorkerInitializeConnection(NULL, NULL, 0);
+
+	/* Enter main loop */
+	for (;;)
+	{
+		int			rc;
+		List	   *sublist;
+		ListCell   *lc;
+		MemoryContext subctx;
+		MemoryContext oldctx;
+		TimestampTz now;
+		long		wait_time = DEFAULT_NAPTIME_PER_CYCLE;
+
+		CHECK_FOR_INTERRUPTS();
+
+		now = GetCurrentTimestamp();
+
+		/* Limit the start retry to once a wal_retrieve_retry_interval */
+		if (TimestampDifferenceExceeds(last_start_time, now,
+									   wal_retrieve_retry_interval))
+		{
+			/* Use temporary context for the database list and worker info. */
+			subctx = AllocSetContextCreate(TopMemoryContext,
+										   "Logical Replication Launcher sublist",
+										   ALLOCSET_DEFAULT_SIZES);
+			oldctx = MemoryContextSwitchTo(subctx);
+
+			/* search for subscriptions to start or stop. */
+			sublist = get_subscription_list();
+
+			/* Start the missing workers for enabled subscriptions. */
+			foreach(lc, sublist)
+			{
+				Subscription *sub = (Subscription *) lfirst(lc);
+				LogicalRepWorker *w;
+
+				if (!sub->enabled)
+					continue;
+
+				LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+				w = logicalrep_worker_find(sub->oid, InvalidOid, false);
+				LWLockRelease(LogicalRepWorkerLock);
+
+				if (w == NULL)
+				{
+					last_start_time = now;
+					wait_time = wal_retrieve_retry_interval;
+
+					logicalrep_worker_launch(sub->dbid, sub->oid, sub->name,
+											 sub->owner, InvalidOid);
+				}
+			}
+
+			/* Switch back to original memory context. */
+			MemoryContextSwitchTo(oldctx);
+			/* Clean the temporary memory. */
+			MemoryContextDelete(subctx);
+		}
+		else
+		{
+			/*
+			 * The wait in previous cycle was interrupted in less than
+			 * wal_retrieve_retry_interval since last worker was started, this
+			 * usually means crash of the worker, so we should retry in
+			 * wal_retrieve_retry_interval again.
+			 */
+			wait_time = wal_retrieve_retry_interval;
+		}
+
+		/* Wait for more work. */
+		rc = WaitLatch(MyLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+					   wait_time,
+					   WAIT_EVENT_LOGICAL_LAUNCHER_MAIN);
+
+		if (rc & WL_LATCH_SET)
+		{
+			ResetLatch(MyLatch);
+			CHECK_FOR_INTERRUPTS();
+		}
+
+		if (ConfigReloadPending)
+		{
+			ConfigReloadPending = false;
+			ProcessConfigFile(PGC_SIGHUP);
+		}
+	}
+
+	/* Not reachable */
+}
+
+/*
+ * Is current process the logical replication launcher?
+ */
+bool
+IsLogicalLauncher(void)
+{
+	return LogicalRepCtx->launcher_pid == MyProcPid;
+}
+
+/*
+ * Returns state of the subscriptions.
+ */
+Datum
+pg_stat_get_subscription(PG_FUNCTION_ARGS)
+{
+#define PG_STAT_GET_SUBSCRIPTION_COLS	8
+	Oid			subid = PG_ARGISNULL(0) ? InvalidOid : PG_GETARG_OID(0);
+	int			i;
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	TupleDesc	tupdesc;
+	Tuplestorestate *tupstore;
+	MemoryContext per_query_ctx;
+	MemoryContext oldcontext;
+
+	/* check to see if caller supports us returning a tuplestore */
+	if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("set-valued function called in context that cannot accept a set")));
+	if (!(rsinfo->allowedModes & SFRM_Materialize))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("materialize mode required, but it is not allowed in this context")));
+
+	/* Build a tuple descriptor for our result type */
+	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
+
+	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
+	oldcontext = MemoryContextSwitchTo(per_query_ctx);
+
+	tupstore = tuplestore_begin_heap(true, false, work_mem);
+	rsinfo->returnMode = SFRM_Materialize;
+	rsinfo->setResult = tupstore;
+	rsinfo->setDesc = tupdesc;
+
+	MemoryContextSwitchTo(oldcontext);
+
+	/* Make sure we get consistent view of the workers. */
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
+	for (i = 0; i < max_logical_replication_workers; i++)
+	{
+		/* for each row */
+		Datum		values[PG_STAT_GET_SUBSCRIPTION_COLS];
+		bool		nulls[PG_STAT_GET_SUBSCRIPTION_COLS];
+		int			worker_pid;
+		LogicalRepWorker worker;
+
+		memcpy(&worker, &LogicalRepCtx->workers[i],
+			   sizeof(LogicalRepWorker));
+		if (!worker.proc || !IsBackendPid(worker.proc->pid))
+			continue;
+
+		if (OidIsValid(subid) && worker.subid != subid)
+			continue;
+
+		worker_pid = worker.proc->pid;
+
+		MemSet(values, 0, sizeof(values));
+		MemSet(nulls, 0, sizeof(nulls));
+
+		values[0] = ObjectIdGetDatum(worker.subid);
+		if (OidIsValid(worker.relid))
+			values[1] = ObjectIdGetDatum(worker.relid);
+		else
+			nulls[1] = true;
+		values[2] = Int32GetDatum(worker_pid);
+		if (XLogRecPtrIsInvalid(worker.last_lsn))
+			nulls[3] = true;
+		else
+			values[3] = LSNGetDatum(worker.last_lsn);
+		if (worker.last_send_time == 0)
+			nulls[4] = true;
+		else
+			values[4] = TimestampTzGetDatum(worker.last_send_time);
+		if (worker.last_recv_time == 0)
+			nulls[5] = true;
+		else
+			values[5] = TimestampTzGetDatum(worker.last_recv_time);
+		if (XLogRecPtrIsInvalid(worker.reply_lsn))
+			nulls[6] = true;
+		else
+			values[6] = LSNGetDatum(worker.reply_lsn);
+		if (worker.reply_time == 0)
+			nulls[7] = true;
+		else
+			values[7] = TimestampTzGetDatum(worker.reply_time);
+
+		tuplestore_putvalues(tupstore, tupdesc, values, nulls);
+
+		/*
+		 * If only a single subscription was requested, and we found it,
+		 * break.
+		 */
+		if (OidIsValid(subid))
+			break;
+	}
+
+	LWLockRelease(LogicalRepWorkerLock);
+
+	/* clean up and return the tuplestore */
+	tuplestore_donestoring(tupstore);
+
+	return (Datum) 0;
+}
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
new file mode 100644
index 0000000..f7d1491
--- /dev/null
+++ b/src/backend/replication/logical/logical.c
@@ -0,0 +1,1840 @@
+/*-------------------------------------------------------------------------
+ * logical.c
+ *	   PostgreSQL logical decoding coordination
+ *
+ * Copyright (c) 2012-2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/logical.c
+ *
+ * NOTES
+ *	  This file coordinates interaction between the various modules that
+ *	  together provide logical decoding, primarily by providing so
+ *	  called LogicalDecodingContexts. The goal is to encapsulate most of the
+ *	  internal complexity for consumers of logical decoding, so they can
+ *	  create and consume a changestream with a low amount of code. Builtin
+ *	  consumers are the walsender and SQL SRF interface, but it's possible to
+ *	  add further ones without changing core code, e.g. to consume changes in
+ *	  a bgworker.
+ *
+ *	  The idea is that a consumer provides three callbacks, one to read WAL,
+ *	  one to prepare a data write, and a final one for actually writing since
+ *	  their implementation depends on the type of consumer.  Check
+ *	  logicalfuncs.c for an example implementation of a fairly simple consumer
+ *	  and an implementation of a WAL reading callback that's suitable for
+ *	  simple consumers.
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/xact.h"
+#include "access/xlog_internal.h"
+#include "fmgr.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "replication/decode.h"
+#include "replication/logical.h"
+#include "replication/origin.h"
+#include "replication/reorderbuffer.h"
+#include "replication/snapbuild.h"
+#include "storage/proc.h"
+#include "storage/procarray.h"
+#include "utils/builtins.h"
+#include "utils/memutils.h"
+
+/* data for errcontext callback */
+typedef struct LogicalErrorCallbackState
+{
+	LogicalDecodingContext *ctx;
+	const char *callback_name;
+	XLogRecPtr	report_location;
+} LogicalErrorCallbackState;
+
+/* wrappers around output plugin callbacks */
+static void output_plugin_error_callback(void *arg);
+static void startup_cb_wrapper(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
+							   bool is_init);
+static void shutdown_cb_wrapper(LogicalDecodingContext *ctx);
+static void begin_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn);
+static void commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+							  XLogRecPtr commit_lsn);
+static void begin_prepare_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn);
+static void prepare_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+							   XLogRecPtr prepare_lsn);
+static void commit_prepared_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+									   XLogRecPtr commit_lsn);
+static void rollback_prepared_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+										 XLogRecPtr prepare_end_lsn, TimestampTz prepare_time);
+static void change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+							  Relation relation, ReorderBufferChange *change);
+static void truncate_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+								int nrelations, Relation relations[], ReorderBufferChange *change);
+static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+							   XLogRecPtr message_lsn, bool transactional,
+							   const char *prefix, Size message_size, const char *message);
+
+/* streaming callbacks */
+static void stream_start_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+									XLogRecPtr first_lsn);
+static void stream_stop_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+								   XLogRecPtr last_lsn);
+static void stream_abort_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+									XLogRecPtr abort_lsn);
+static void stream_prepare_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+									  XLogRecPtr prepare_lsn);
+static void stream_commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+									 XLogRecPtr commit_lsn);
+static void stream_change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+									 Relation relation, ReorderBufferChange *change);
+static void stream_message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+									  XLogRecPtr message_lsn, bool transactional,
+									  const char *prefix, Size message_size, const char *message);
+static void stream_truncate_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+									   int nrelations, Relation relations[], ReorderBufferChange *change);
+
+static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugin);
+
+/*
+ * Make sure the current settings & environment are capable of doing logical
+ * decoding.
+ */
+void
+CheckLogicalDecodingRequirements(void)
+{
+	CheckSlotRequirements();
+
+	/*
+	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
+	 * needs the same check.
+	 */
+
+	if (wal_level < WAL_LEVEL_LOGICAL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("logical decoding requires wal_level >= logical")));
+
+	if (MyDatabaseId == InvalidOid)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("logical decoding requires a database connection")));
+
+	/* ----
+	 * TODO: We got to change that someday soon...
+	 *
+	 * There's basically three things missing to allow this:
+	 * 1) We need to be able to correctly and quickly identify the timeline a
+	 *	  LSN belongs to
+	 * 2) We need to force hot_standby_feedback to be enabled at all times so
+	 *	  the primary cannot remove rows we need.
+	 * 3) support dropping replication slots referring to a database, in
+	 *	  dbase_redo. There can't be any active ones due to HS recovery
+	 *	  conflicts, so that should be relatively easy.
+	 * ----
+	 */
+	if (RecoveryInProgress())
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("logical decoding cannot be used while in recovery")));
+}
+
+/*
+ * Helper function for CreateInitDecodingContext() and
+ * CreateDecodingContext() performing common tasks.
+ */
+static LogicalDecodingContext *
+StartupDecodingContext(List *output_plugin_options,
+					   XLogRecPtr start_lsn,
+					   TransactionId xmin_horizon,
+					   bool need_full_snapshot,
+					   bool fast_forward,
+					   XLogReaderRoutine *xl_routine,
+					   LogicalOutputPluginWriterPrepareWrite prepare_write,
+					   LogicalOutputPluginWriterWrite do_write,
+					   LogicalOutputPluginWriterUpdateProgress update_progress)
+{
+	ReplicationSlot *slot;
+	MemoryContext context,
+				old_context;
+	LogicalDecodingContext *ctx;
+
+	/* shorter lines... */
+	slot = MyReplicationSlot;
+
+	context = AllocSetContextCreate(CurrentMemoryContext,
+									"Logical decoding context",
+									ALLOCSET_DEFAULT_SIZES);
+	old_context = MemoryContextSwitchTo(context);
+	ctx = palloc0(sizeof(LogicalDecodingContext));
+
+	ctx->context = context;
+
+	/*
+	 * (re-)load output plugins, so we detect a bad (removed) output plugin
+	 * now.
+	 */
+	if (!fast_forward)
+		LoadOutputPlugin(&ctx->callbacks, NameStr(slot->data.plugin));
+
+	/*
+	 * Now that the slot's xmin has been set, we can announce ourselves as a
+	 * logical decoding backend which doesn't need to be checked individually
+	 * when computing the xmin horizon because the xmin is enforced via
+	 * replication slots.
+	 *
+	 * We can only do so if we're outside of a transaction (i.e. the case when
+	 * streaming changes via walsender), otherwise an already setup
+	 * snapshot/xid would end up being ignored. That's not a particularly
+	 * bothersome restriction since the SQL interface can't be used for
+	 * streaming anyway.
+	 */
+	if (!IsTransactionOrTransactionBlock())
+	{
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_LOGICAL_DECODING;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+	}
+
+	ctx->slot = slot;
+
+	ctx->reader = XLogReaderAllocate(wal_segment_size, NULL, xl_routine, ctx);
+	if (!ctx->reader)
+		ereport(ERROR,
+				(errcode(ERRCODE_OUT_OF_MEMORY),
+				 errmsg("out of memory")));
+
+	ctx->reorder = ReorderBufferAllocate();
+	ctx->snapshot_builder =
+		AllocateSnapshotBuilder(ctx->reorder, xmin_horizon, start_lsn,
+								need_full_snapshot, slot->data.initial_consistent_point);
+
+	ctx->reorder->private_data = ctx;
+
+	/* wrap output plugin callbacks, so we can add error context information */
+	ctx->reorder->begin = begin_cb_wrapper;
+	ctx->reorder->apply_change = change_cb_wrapper;
+	ctx->reorder->apply_truncate = truncate_cb_wrapper;
+	ctx->reorder->commit = commit_cb_wrapper;
+	ctx->reorder->message = message_cb_wrapper;
+
+	/*
+	 * To support streaming, we require start/stop/abort/commit/change
+	 * callbacks. The message and truncate callbacks are optional, similar to
+	 * regular output plugins. We however enable streaming when at least one
+	 * of the methods is enabled so that we can easily identify missing
+	 * methods.
+	 *
+	 * We decide it here, but only check it later in the wrappers.
+	 */
+	ctx->streaming = (ctx->callbacks.stream_start_cb != NULL) ||
+		(ctx->callbacks.stream_stop_cb != NULL) ||
+		(ctx->callbacks.stream_abort_cb != NULL) ||
+		(ctx->callbacks.stream_commit_cb != NULL) ||
+		(ctx->callbacks.stream_change_cb != NULL) ||
+		(ctx->callbacks.stream_message_cb != NULL) ||
+		(ctx->callbacks.stream_truncate_cb != NULL);
+
+	/*
+	 * streaming callbacks
+	 *
+	 * stream_message and stream_truncate callbacks are optional, so we do not
+	 * fail with ERROR when missing, but the wrappers simply do nothing. We
+	 * must set the ReorderBuffer callbacks to something, otherwise the calls
+	 * from there will crash (we don't want to move the checks there).
+	 */
+	ctx->reorder->stream_start = stream_start_cb_wrapper;
+	ctx->reorder->stream_stop = stream_stop_cb_wrapper;
+	ctx->reorder->stream_abort = stream_abort_cb_wrapper;
+	ctx->reorder->stream_prepare = stream_prepare_cb_wrapper;
+	ctx->reorder->stream_commit = stream_commit_cb_wrapper;
+	ctx->reorder->stream_change = stream_change_cb_wrapper;
+	ctx->reorder->stream_message = stream_message_cb_wrapper;
+	ctx->reorder->stream_truncate = stream_truncate_cb_wrapper;
+
+
+	/*
+	 * To support two-phase logical decoding, we require
+	 * begin_prepare/prepare/commit-prepare/abort-prepare callbacks. The
+	 * filter_prepare callback is optional. We however enable two-phase
+	 * logical decoding when at least one of the methods is enabled so that we
+	 * can easily identify missing methods.
+	 *
+	 * We decide it here, but only check it later in the wrappers.
+	 */
+	ctx->twophase = (ctx->callbacks.begin_prepare_cb != NULL) ||
+		(ctx->callbacks.prepare_cb != NULL) ||
+		(ctx->callbacks.commit_prepared_cb != NULL) ||
+		(ctx->callbacks.rollback_prepared_cb != NULL) ||
+		(ctx->callbacks.stream_prepare_cb != NULL) ||
+		(ctx->callbacks.filter_prepare_cb != NULL);
+
+	/*
+	 * Callback to support decoding at prepare time.
+	 */
+	ctx->reorder->begin_prepare = begin_prepare_cb_wrapper;
+	ctx->reorder->prepare = prepare_cb_wrapper;
+	ctx->reorder->commit_prepared = commit_prepared_cb_wrapper;
+	ctx->reorder->rollback_prepared = rollback_prepared_cb_wrapper;
+
+	ctx->out = makeStringInfo();
+	ctx->prepare_write = prepare_write;
+	ctx->write = do_write;
+	ctx->update_progress = update_progress;
+
+	ctx->output_plugin_options = output_plugin_options;
+
+	ctx->fast_forward = fast_forward;
+
+	MemoryContextSwitchTo(old_context);
+
+	return ctx;
+}
+
+/*
+ * Create a new decoding context, for a new logical slot.
+ *
+ * plugin -- contains the name of the output plugin
+ * output_plugin_options -- contains options passed to the output plugin
+ * need_full_snapshot -- if true, must obtain a snapshot able to read all
+ *		tables; if false, one that can read only catalogs is acceptable.
+ * restart_lsn -- if given as invalid, it's this routine's responsibility to
+ *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
+ *		Otherwise, we set for decoding to start from the given LSN without
+ *		marking WAL reserved beforehand.  In that scenario, it's up to the
+ *		caller to guarantee that WAL remains available.
+ * xl_routine -- XLogReaderRoutine for underlying XLogReader
+ * prepare_write, do_write, update_progress --
+ *		callbacks that perform the use-case dependent, actual, work.
+ *
+ * Needs to be called while in a memory context that's at least as long lived
+ * as the decoding context because further memory contexts will be created
+ * inside it.
+ *
+ * Returns an initialized decoding context after calling the output plugin's
+ * startup function.
+ */
+LogicalDecodingContext *
+CreateInitDecodingContext(const char *plugin,
+						  List *output_plugin_options,
+						  bool need_full_snapshot,
+						  XLogRecPtr restart_lsn,
+						  XLogReaderRoutine *xl_routine,
+						  LogicalOutputPluginWriterPrepareWrite prepare_write,
+						  LogicalOutputPluginWriterWrite do_write,
+						  LogicalOutputPluginWriterUpdateProgress update_progress)
+{
+	TransactionId xmin_horizon = InvalidTransactionId;
+	ReplicationSlot *slot;
+	NameData	plugin_name;
+	LogicalDecodingContext *ctx;
+	MemoryContext old_context;
+
+	/* shorter lines... */
+	slot = MyReplicationSlot;
+
+	/* first some sanity checks that are unlikely to be violated */
+	if (slot == NULL)
+		elog(ERROR, "cannot perform logical decoding without an acquired slot");
+
+	if (plugin == NULL)
+		elog(ERROR, "cannot initialize logical decoding without a specified plugin");
+
+	/* Make sure the passed slot is suitable. These are user facing errors. */
+	if (SlotIsPhysical(slot))
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot use physical replication slot for logical decoding")));
+
+	if (slot->data.database != MyDatabaseId)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("replication slot \"%s\" was not created in this database",
+						NameStr(slot->data.name))));
+
+	if (IsTransactionState() &&
+		GetTopTransactionIdIfAny() != InvalidTransactionId)
+		ereport(ERROR,
+				(errcode(ERRCODE_ACTIVE_SQL_TRANSACTION),
+				 errmsg("cannot create logical replication slot in transaction that has performed writes")));
+
+	/*
+	 * Register output plugin name with slot.  We need the mutex to avoid
+	 * concurrent reading of a partially copied string.  But we don't want any
+	 * complicated code while holding a spinlock, so do namestrcpy() outside.
+	 */
+	namestrcpy(&plugin_name, plugin);
+	SpinLockAcquire(&slot->mutex);
+	slot->data.plugin = plugin_name;
+	SpinLockRelease(&slot->mutex);
+
+	if (XLogRecPtrIsInvalid(restart_lsn))
+		ReplicationSlotReserveWal();
+	else
+	{
+		SpinLockAcquire(&slot->mutex);
+		slot->data.restart_lsn = restart_lsn;
+		SpinLockRelease(&slot->mutex);
+	}
+
+	/* ----
+	 * This is a bit tricky: We need to determine a safe xmin horizon to start
+	 * decoding from, to avoid starting from a running xacts record referring
+	 * to xids whose rows have been vacuumed or pruned
+	 * already. GetOldestSafeDecodingTransactionId() returns such a value, but
+	 * without further interlock its return value might immediately be out of
+	 * date.
+	 *
+	 * So we have to acquire the ProcArrayLock to prevent computation of new
+	 * xmin horizons by other backends, get the safe decoding xid, and inform
+	 * the slot machinery about the new limit. Once that's done the
+	 * ProcArrayLock can be released as the slot machinery now is
+	 * protecting against vacuum.
+	 *
+	 * Note that, temporarily, the data, not just the catalog, xmin has to be
+	 * reserved if a data snapshot is to be exported.  Otherwise the initial
+	 * data snapshot created here is not guaranteed to be valid. After that
+	 * the data xmin doesn't need to be managed anymore and the global xmin
+	 * should be recomputed. As we are fine with losing the pegged data xmin
+	 * after crash - no chance a snapshot would get exported anymore - we can
+	 * get away with just setting the slot's
+	 * effective_xmin. ReplicationSlotRelease will reset it again.
+	 *
+	 * ----
+	 */
+	LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+
+	xmin_horizon = GetOldestSafeDecodingTransactionId(!need_full_snapshot);
+
+	SpinLockAcquire(&slot->mutex);
+	slot->effective_catalog_xmin = xmin_horizon;
+	slot->data.catalog_xmin = xmin_horizon;
+	if (need_full_snapshot)
+		slot->effective_xmin = xmin_horizon;
+	SpinLockRelease(&slot->mutex);
+
+	ReplicationSlotsComputeRequiredXmin(true);
+
+	LWLockRelease(ProcArrayLock);
+
+	ReplicationSlotMarkDirty();
+	ReplicationSlotSave();
+
+	ctx = StartupDecodingContext(NIL, restart_lsn, xmin_horizon,
+								 need_full_snapshot, false,
+								 xl_routine, prepare_write, do_write,
+								 update_progress);
+
+	/* call output plugin initialization callback */
+	old_context = MemoryContextSwitchTo(ctx->context);
+	if (ctx->callbacks.startup_cb != NULL)
+		startup_cb_wrapper(ctx, &ctx->options, true);
+	MemoryContextSwitchTo(old_context);
+
+	/*
+	 * We allow decoding of prepared transactions iff the two_phase option is
+	 * enabled at the time of slot creation.
+	 */
+	ctx->twophase &= MyReplicationSlot->data.two_phase;
+
+	ctx->reorder->output_rewrites = ctx->options.receive_rewrites;
+
+	return ctx;
+}
+
+/*
+ * Create a new decoding context, for a logical slot that has previously been
+ * used already.
+ *
+ * start_lsn
+ *		The LSN at which to start decoding.  If InvalidXLogRecPtr, restart
+ *		from the slot's confirmed_flush; otherwise, start from the specified
+ *		location (but move it forwards to confirmed_flush if it's older than
+ *		that, see below).
+ *
+ * output_plugin_options
+ *		options passed to the output plugin.
+ *
+ * fast_forward
+ *		bypass the generation of logical changes.
+ *
+ * xl_routine
+ *		XLogReaderRoutine used by underlying xlogreader
+ *
+ * prepare_write, do_write, update_progress
+ *		callbacks that have to be filled to perform the use-case dependent,
+ *		actual work.
+ *
+ * Needs to be called while in a memory context that's at least as long lived
+ * as the decoding context because further memory contexts will be created
+ * inside it.
+ *
+ * Returns an initialized decoding context after calling the output plugin's
+ * startup function.
+ */
+LogicalDecodingContext *
+CreateDecodingContext(XLogRecPtr start_lsn,
+					  List *output_plugin_options,
+					  bool fast_forward,
+					  XLogReaderRoutine *xl_routine,
+					  LogicalOutputPluginWriterPrepareWrite prepare_write,
+					  LogicalOutputPluginWriterWrite do_write,
+					  LogicalOutputPluginWriterUpdateProgress update_progress)
+{
+	LogicalDecodingContext *ctx;
+	ReplicationSlot *slot;
+	MemoryContext old_context;
+
+	/* shorter lines... */
+	slot = MyReplicationSlot;
+
+	/* first some sanity checks that are unlikely to be violated */
+	if (slot == NULL)
+		elog(ERROR, "cannot perform logical decoding without an acquired slot");
+
+	/* make sure the passed slot is suitable, these are user facing errors */
+	if (SlotIsPhysical(slot))
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot use physical replication slot for logical decoding")));
+
+	if (slot->data.database != MyDatabaseId)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("replication slot \"%s\" was not created in this database",
+						NameStr(slot->data.name))));
+
+	if (start_lsn == InvalidXLogRecPtr)
+	{
+		/* continue from last position */
+		start_lsn = slot->data.confirmed_flush;
+	}
+	else if (start_lsn < slot->data.confirmed_flush)
+	{
+		/*
+		 * It might seem like we should error out in this case, but it's
+		 * pretty common for a client to acknowledge a LSN it doesn't have to
+		 * do anything for, and thus didn't store persistently, because the
+		 * xlog records didn't result in anything relevant for logical
+		 * decoding. Clients have to be able to do that to support synchronous
+		 * replication.
+		 */
+		elog(DEBUG1, "cannot stream from %X/%X, minimum is %X/%X, forwarding",
+			 LSN_FORMAT_ARGS(start_lsn),
+			 LSN_FORMAT_ARGS(slot->data.confirmed_flush));
+
+		start_lsn = slot->data.confirmed_flush;
+	}
+
+	ctx = StartupDecodingContext(output_plugin_options,
+								 start_lsn, InvalidTransactionId, false,
+								 fast_forward, xl_routine, prepare_write,
+								 do_write, update_progress);
+
+	/* call output plugin initialization callback */
+	old_context = MemoryContextSwitchTo(ctx->context);
+	if (ctx->callbacks.startup_cb != NULL)
+		startup_cb_wrapper(ctx, &ctx->options, false);
+	MemoryContextSwitchTo(old_context);
+
+	/*
+	 * We allow decoding of prepared transactions iff the two_phase option is
+	 * enabled at the time of slot creation.
+	 */
+	ctx->twophase &= MyReplicationSlot->data.two_phase;
+
+	ctx->reorder->output_rewrites = ctx->options.receive_rewrites;
+
+	ereport(LOG,
+			(errmsg("starting logical decoding for slot \"%s\"",
+					NameStr(slot->data.name)),
+			 errdetail("Streaming transactions committing after %X/%X, reading WAL from %X/%X.",
+					   LSN_FORMAT_ARGS(slot->data.confirmed_flush),
+					   LSN_FORMAT_ARGS(slot->data.restart_lsn))));
+
+	return ctx;
+}
+
+/*
+ * Returns true if a consistent initial decoding snapshot has been built.
+ */
+bool
+DecodingContextReady(LogicalDecodingContext *ctx)
+{
+	return SnapBuildCurrentState(ctx->snapshot_builder) == SNAPBUILD_CONSISTENT;
+}
+
+/*
+ * Read from the decoding slot, until it is ready to start extracting changes.
+ */
+void
+DecodingContextFindStartpoint(LogicalDecodingContext *ctx)
+{
+	ReplicationSlot *slot = ctx->slot;
+
+	/* Initialize from where to start reading WAL. */
+	XLogBeginRead(ctx->reader, slot->data.restart_lsn);
+
+	elog(DEBUG1, "searching for logical decoding starting point, starting at %X/%X",
+		 LSN_FORMAT_ARGS(slot->data.restart_lsn));
+
+	/* Wait for a consistent starting point */
+	for (;;)
+	{
+		XLogRecord *record;
+		char	   *err = NULL;
+
+		/* the read_page callback waits for new WAL */
+		record = XLogReadRecord(ctx->reader, &err);
+		if (err)
+			elog(ERROR, "%s", err);
+		if (!record)
+			elog(ERROR, "no record found"); /* shouldn't happen */
+
+		LogicalDecodingProcessRecord(ctx, ctx->reader);
+
+		/* only continue till we found a consistent spot */
+		if (DecodingContextReady(ctx))
+			break;
+
+		CHECK_FOR_INTERRUPTS();
+	}
+
+	SpinLockAcquire(&slot->mutex);
+	slot->data.confirmed_flush = ctx->reader->EndRecPtr;
+	slot->data.initial_consistent_point = ctx->reader->EndRecPtr;
+	SpinLockRelease(&slot->mutex);
+}
+
+/*
+ * Free a previously allocated decoding context, invoking the shutdown
+ * callback if necessary.
+ */
+void
+FreeDecodingContext(LogicalDecodingContext *ctx)
+{
+	if (ctx->callbacks.shutdown_cb != NULL)
+		shutdown_cb_wrapper(ctx);
+
+	ReorderBufferFree(ctx->reorder);
+	FreeSnapshotBuilder(ctx->snapshot_builder);
+	XLogReaderFree(ctx->reader);
+	MemoryContextDelete(ctx->context);
+}
+
+/*
+ * Prepare a write using the context's output routine.
+ */
+void
+OutputPluginPrepareWrite(struct LogicalDecodingContext *ctx, bool last_write)
+{
+	if (!ctx->accept_writes)
+		elog(ERROR, "writes are only accepted in commit, begin and change callbacks");
+
+	ctx->prepare_write(ctx, ctx->write_location, ctx->write_xid, last_write);
+	ctx->prepared_write = true;
+}
+
+/*
+ * Perform a write using the context's output routine.
+ */
+void
+OutputPluginWrite(struct LogicalDecodingContext *ctx, bool last_write)
+{
+	if (!ctx->prepared_write)
+		elog(ERROR, "OutputPluginPrepareWrite needs to be called before OutputPluginWrite");
+
+	ctx->write(ctx, ctx->write_location, ctx->write_xid, last_write);
+	ctx->prepared_write = false;
+}
+
+/*
+ * Update progress tracking (if supported).
+ */
+void
+OutputPluginUpdateProgress(struct LogicalDecodingContext *ctx)
+{
+	if (!ctx->update_progress)
+		return;
+
+	ctx->update_progress(ctx, ctx->write_location, ctx->write_xid);
+}
+
+/*
+ * Load the output plugin, lookup its output plugin init function, and check
+ * that it provides the required callbacks.
+ */
+static void
+LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugin)
+{
+	LogicalOutputPluginInit plugin_init;
+
+	plugin_init = (LogicalOutputPluginInit)
+		load_external_function(plugin, "_PG_output_plugin_init", false, NULL);
+
+	if (plugin_init == NULL)
+		elog(ERROR, "output plugins have to declare the _PG_output_plugin_init symbol");
+
+	/* ask the output plugin to fill the callback struct */
+	plugin_init(callbacks);
+
+	if (callbacks->begin_cb == NULL)
+		elog(ERROR, "output plugins have to register a begin callback");
+	if (callbacks->change_cb == NULL)
+		elog(ERROR, "output plugins have to register a change callback");
+	if (callbacks->commit_cb == NULL)
+		elog(ERROR, "output plugins have to register a commit callback");
+}
+
+static void
+output_plugin_error_callback(void *arg)
+{
+	LogicalErrorCallbackState *state = (LogicalErrorCallbackState *) arg;
+
+	/* not all callbacks have an associated LSN  */
+	if (state->report_location != InvalidXLogRecPtr)
+		errcontext("slot \"%s\", output plugin \"%s\", in the %s callback, associated LSN %X/%X",
+				   NameStr(state->ctx->slot->data.name),
+				   NameStr(state->ctx->slot->data.plugin),
+				   state->callback_name,
+				   LSN_FORMAT_ARGS(state->report_location));
+	else
+		errcontext("slot \"%s\", output plugin \"%s\", in the %s callback",
+				   NameStr(state->ctx->slot->data.name),
+				   NameStr(state->ctx->slot->data.plugin),
+				   state->callback_name);
+}
+
+static void
+startup_cb_wrapper(LogicalDecodingContext *ctx, OutputPluginOptions *opt, bool is_init)
+{
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "startup";
+	state.report_location = InvalidXLogRecPtr;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = false;
+	ctx->end_xact = false;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.startup_cb(ctx, opt, is_init);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+shutdown_cb_wrapper(LogicalDecodingContext *ctx)
+{
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "shutdown";
+	state.report_location = InvalidXLogRecPtr;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = false;
+	ctx->end_xact = false;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.shutdown_cb(ctx);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+
+/*
+ * Callbacks for ReorderBuffer which add in some more information and then call
+ * output_plugin.h plugins.
+ */
+static void
+begin_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "begin";
+	state.report_location = txn->first_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+	ctx->write_location = txn->first_lsn;
+	ctx->end_xact = false;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.begin_cb(ctx, txn);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				  XLogRecPtr commit_lsn)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "commit";
+	state.report_location = txn->final_lsn; /* beginning of commit record */
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+	ctx->write_location = txn->end_lsn; /* points to the end of the record */
+	ctx->end_xact = true;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.commit_cb(ctx, txn, commit_lsn);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+/*
+ * The functionality of begin_prepare is quite similar to begin with the
+ * exception that this will have gid (global transaction id) information which
+ * can be used by plugin. Now, we thought about extending the existing begin
+ * but that would break the replication protocol and additionally this looks
+ * cleaner.
+ */
+static void
+begin_prepare_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* We're only supposed to call this when two-phase commits are supported */
+	Assert(ctx->twophase);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "begin_prepare";
+	state.report_location = txn->first_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+	ctx->write_location = txn->first_lsn;
+	ctx->end_xact = false;
+
+	/*
+	 * If the plugin supports two-phase commits then begin prepare callback is
+	 * mandatory
+	 */
+	if (ctx->callbacks.begin_prepare_cb == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("logical replication at prepare time requires a %s callback",
+						"begin_prepare_cb")));
+
+	/* do the actual work: call callback */
+	ctx->callbacks.begin_prepare_cb(ctx, txn);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+prepare_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				   XLogRecPtr prepare_lsn)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* We're only supposed to call this when two-phase commits are supported */
+	Assert(ctx->twophase);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "prepare";
+	state.report_location = txn->final_lsn; /* beginning of prepare record */
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+	ctx->write_location = txn->end_lsn; /* points to the end of the record */
+	ctx->end_xact = true;
+
+	/*
+	 * If the plugin supports two-phase commits then prepare callback is
+	 * mandatory
+	 */
+	if (ctx->callbacks.prepare_cb == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("logical replication at prepare time requires a %s callback",
+						"prepare_cb")));
+
+	/* do the actual work: call callback */
+	ctx->callbacks.prepare_cb(ctx, txn, prepare_lsn);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+commit_prepared_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+						   XLogRecPtr commit_lsn)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* We're only supposed to call this when two-phase commits are supported */
+	Assert(ctx->twophase);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "commit_prepared";
+	state.report_location = txn->final_lsn; /* beginning of commit record */
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+	ctx->write_location = txn->end_lsn; /* points to the end of the record */
+	ctx->end_xact = true;
+
+	/*
+	 * If the plugin support two-phase commits then commit prepared callback
+	 * is mandatory
+	 */
+	if (ctx->callbacks.commit_prepared_cb == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("logical replication at prepare time requires a %s callback",
+						"commit_prepared_cb")));
+
+	/* do the actual work: call callback */
+	ctx->callbacks.commit_prepared_cb(ctx, txn, commit_lsn);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+rollback_prepared_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+							 XLogRecPtr prepare_end_lsn,
+							 TimestampTz prepare_time)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* We're only supposed to call this when two-phase commits are supported */
+	Assert(ctx->twophase);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "rollback_prepared";
+	state.report_location = txn->final_lsn; /* beginning of commit record */
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+	ctx->write_location = txn->end_lsn; /* points to the end of the record */
+	ctx->end_xact = true;
+
+	/*
+	 * If the plugin support two-phase commits then rollback prepared callback
+	 * is mandatory
+	 */
+	if (ctx->callbacks.rollback_prepared_cb == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("logical replication at prepare time requires a %s callback",
+						"rollback_prepared_cb")));
+
+	/* do the actual work: call callback */
+	ctx->callbacks.rollback_prepared_cb(ctx, txn, prepare_end_lsn,
+										prepare_time);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				  Relation relation, ReorderBufferChange *change)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "change";
+	state.report_location = change->lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+
+	/*
+	 * report this change's lsn so replies from clients can give an up2date
+	 * answer. This won't ever be enough (and shouldn't be!) to confirm
+	 * receipt of this transaction, but it might allow another transaction's
+	 * commit to be confirmed with one message.
+	 */
+	ctx->write_location = change->lsn;
+
+	ctx->end_xact = false;
+
+	ctx->callbacks.change_cb(ctx, txn, relation, change);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+truncate_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+					int nrelations, Relation relations[], ReorderBufferChange *change)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	if (!ctx->callbacks.truncate_cb)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "truncate";
+	state.report_location = change->lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+
+	/*
+	 * report this change's lsn so replies from clients can give an up2date
+	 * answer. This won't ever be enough (and shouldn't be!) to confirm
+	 * receipt of this transaction, but it might allow another transaction's
+	 * commit to be confirmed with one message.
+	 */
+	ctx->write_location = change->lsn;
+
+	ctx->end_xact = false;
+
+	ctx->callbacks.truncate_cb(ctx, txn, nrelations, relations, change);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+bool
+filter_prepare_cb_wrapper(LogicalDecodingContext *ctx, TransactionId xid,
+						  const char *gid)
+{
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+	bool		ret;
+
+	Assert(!ctx->fast_forward);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "filter_prepare";
+	state.report_location = InvalidXLogRecPtr;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = false;
+	ctx->end_xact = false;
+
+	/* do the actual work: call callback */
+	ret = ctx->callbacks.filter_prepare_cb(ctx, xid, gid);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+
+	return ret;
+}
+
+bool
+filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id)
+{
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+	bool		ret;
+
+	Assert(!ctx->fast_forward);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "filter_by_origin";
+	state.report_location = InvalidXLogRecPtr;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = false;
+	ctx->end_xact = false;
+
+	/* do the actual work: call callback */
+	ret = ctx->callbacks.filter_by_origin_cb(ctx, origin_id);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+
+	return ret;
+}
+
+static void
+message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				   XLogRecPtr message_lsn, bool transactional,
+				   const char *prefix, Size message_size, const char *message)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	if (ctx->callbacks.message_cb == NULL)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "message";
+	state.report_location = message_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
+	ctx->write_location = message_lsn;
+	ctx->end_xact = false;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.message_cb(ctx, txn, message_lsn, transactional, prefix,
+							  message_size, message);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+stream_start_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+						XLogRecPtr first_lsn)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* We're only supposed to call this when streaming is supported. */
+	Assert(ctx->streaming);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "stream_start";
+	state.report_location = first_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+
+	/*
+	 * report this message's lsn so replies from clients can give an up2date
+	 * answer. This won't ever be enough (and shouldn't be!) to confirm
+	 * receipt of this transaction, but it might allow another transaction's
+	 * commit to be confirmed with one message.
+	 */
+	ctx->write_location = first_lsn;
+
+	ctx->end_xact = false;
+
+	/* in streaming mode, stream_start_cb is required */
+	if (ctx->callbacks.stream_start_cb == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("logical streaming requires a %s callback",
+						"stream_start_cb")));
+
+	ctx->callbacks.stream_start_cb(ctx, txn);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+stream_stop_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+					   XLogRecPtr last_lsn)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* We're only supposed to call this when streaming is supported. */
+	Assert(ctx->streaming);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "stream_stop";
+	state.report_location = last_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+
+	/*
+	 * report this message's lsn so replies from clients can give an up2date
+	 * answer. This won't ever be enough (and shouldn't be!) to confirm
+	 * receipt of this transaction, but it might allow another transaction's
+	 * commit to be confirmed with one message.
+	 */
+	ctx->write_location = last_lsn;
+
+	ctx->end_xact = false;
+
+	/* in streaming mode, stream_stop_cb is required */
+	if (ctx->callbacks.stream_stop_cb == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("logical streaming requires a %s callback",
+						"stream_stop_cb")));
+
+	ctx->callbacks.stream_stop_cb(ctx, txn);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+stream_abort_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+						XLogRecPtr abort_lsn)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* We're only supposed to call this when streaming is supported. */
+	Assert(ctx->streaming);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "stream_abort";
+	state.report_location = abort_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+	ctx->write_location = abort_lsn;
+	ctx->end_xact = true;
+
+	/* in streaming mode, stream_abort_cb is required */
+	if (ctx->callbacks.stream_abort_cb == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("logical streaming requires a %s callback",
+						"stream_abort_cb")));
+
+	ctx->callbacks.stream_abort_cb(ctx, txn, abort_lsn);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+stream_prepare_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+						  XLogRecPtr prepare_lsn)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/*
+	 * We're only supposed to call this when streaming and two-phase commits
+	 * are supported.
+	 */
+	Assert(ctx->streaming);
+	Assert(ctx->twophase);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "stream_prepare";
+	state.report_location = txn->final_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+	ctx->write_location = txn->end_lsn;
+	ctx->end_xact = true;
+
+	/* in streaming mode with two-phase commits, stream_prepare_cb is required */
+	if (ctx->callbacks.stream_prepare_cb == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("logical streaming at prepare time requires a %s callback",
+						"stream_prepare_cb")));
+
+	ctx->callbacks.stream_prepare_cb(ctx, txn, prepare_lsn);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+stream_commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+						 XLogRecPtr commit_lsn)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* We're only supposed to call this when streaming is supported. */
+	Assert(ctx->streaming);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "stream_commit";
+	state.report_location = txn->final_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+	ctx->write_location = txn->end_lsn;
+	ctx->end_xact = true;
+
+	/* in streaming mode, stream_commit_cb is required */
+	if (ctx->callbacks.stream_commit_cb == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("logical streaming requires a %s callback",
+						"stream_commit_cb")));
+
+	ctx->callbacks.stream_commit_cb(ctx, txn, commit_lsn);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+stream_change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+						 Relation relation, ReorderBufferChange *change)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* We're only supposed to call this when streaming is supported. */
+	Assert(ctx->streaming);
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "stream_change";
+	state.report_location = change->lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+
+	/*
+	 * report this change's lsn so replies from clients can give an up2date
+	 * answer. This won't ever be enough (and shouldn't be!) to confirm
+	 * receipt of this transaction, but it might allow another transaction's
+	 * commit to be confirmed with one message.
+	 */
+	ctx->write_location = change->lsn;
+
+	ctx->end_xact = false;
+
+	/* in streaming mode, stream_change_cb is required */
+	if (ctx->callbacks.stream_change_cb == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("logical streaming requires a %s callback",
+						"stream_change_cb")));
+
+	ctx->callbacks.stream_change_cb(ctx, txn, relation, change);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+stream_message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+						  XLogRecPtr message_lsn, bool transactional,
+						  const char *prefix, Size message_size, const char *message)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* We're only supposed to call this when streaming is supported. */
+	Assert(ctx->streaming);
+
+	/* this callback is optional */
+	if (ctx->callbacks.stream_message_cb == NULL)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "stream_message";
+	state.report_location = message_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
+	ctx->write_location = message_lsn;
+	ctx->end_xact = false;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.stream_message_cb(ctx, txn, message_lsn, transactional, prefix,
+									 message_size, message);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+static void
+stream_truncate_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+						   int nrelations, Relation relations[],
+						   ReorderBufferChange *change)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	Assert(!ctx->fast_forward);
+
+	/* We're only supposed to call this when streaming is supported. */
+	Assert(ctx->streaming);
+
+	/* this callback is optional */
+	if (!ctx->callbacks.stream_truncate_cb)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "stream_truncate";
+	state.report_location = change->lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn->xid;
+
+	/*
+	 * report this change's lsn so replies from clients can give an up2date
+	 * answer. This won't ever be enough (and shouldn't be!) to confirm
+	 * receipt of this transaction, but it might allow another transaction's
+	 * commit to be confirmed with one message.
+	 */
+	ctx->write_location = change->lsn;
+
+	ctx->end_xact = false;
+
+	ctx->callbacks.stream_truncate_cb(ctx, txn, nrelations, relations, change);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
+/*
+ * Set the required catalog xmin horizon for historic snapshots in the current
+ * replication slot.
+ *
+ * Note that in the most cases, we won't be able to immediately use the xmin
+ * to increase the xmin horizon: we need to wait till the client has confirmed
+ * receiving current_lsn with LogicalConfirmReceivedLocation().
+ */
+void
+LogicalIncreaseXminForSlot(XLogRecPtr current_lsn, TransactionId xmin)
+{
+	bool		updated_xmin = false;
+	ReplicationSlot *slot;
+
+	slot = MyReplicationSlot;
+
+	Assert(slot != NULL);
+
+	SpinLockAcquire(&slot->mutex);
+
+	/*
+	 * don't overwrite if we already have a newer xmin. This can happen if we
+	 * restart decoding in a slot.
+	 */
+	if (TransactionIdPrecedesOrEquals(xmin, slot->data.catalog_xmin))
+	{
+	}
+
+	/*
+	 * If the client has already confirmed up to this lsn, we directly can
+	 * mark this as accepted. This can happen if we restart decoding in a
+	 * slot.
+	 */
+	else if (current_lsn <= slot->data.confirmed_flush)
+	{
+		slot->candidate_catalog_xmin = xmin;
+		slot->candidate_xmin_lsn = current_lsn;
+
+		/* our candidate can directly be used */
+		updated_xmin = true;
+	}
+
+	/*
+	 * Only increase if the previous values have been applied, otherwise we
+	 * might never end up updating if the receiver acks too slowly.
+	 */
+	else if (slot->candidate_xmin_lsn == InvalidXLogRecPtr)
+	{
+		slot->candidate_catalog_xmin = xmin;
+		slot->candidate_xmin_lsn = current_lsn;
+	}
+	SpinLockRelease(&slot->mutex);
+
+	/* candidate already valid with the current flush position, apply */
+	if (updated_xmin)
+		LogicalConfirmReceivedLocation(slot->data.confirmed_flush);
+}
+
+/*
+ * Mark the minimal LSN (restart_lsn) we need to read to replay all
+ * transactions that have not yet committed at current_lsn.
+ *
+ * Just like LogicalIncreaseXminForSlot this only takes effect when the
+ * client has confirmed to have received current_lsn.
+ */
+void
+LogicalIncreaseRestartDecodingForSlot(XLogRecPtr current_lsn, XLogRecPtr restart_lsn)
+{
+	bool		updated_lsn = false;
+	ReplicationSlot *slot;
+
+	slot = MyReplicationSlot;
+
+	Assert(slot != NULL);
+	Assert(restart_lsn != InvalidXLogRecPtr);
+	Assert(current_lsn != InvalidXLogRecPtr);
+
+	SpinLockAcquire(&slot->mutex);
+
+	/* don't overwrite if have a newer restart lsn */
+	if (restart_lsn <= slot->data.restart_lsn)
+	{
+	}
+
+	/*
+	 * We might have already flushed far enough to directly accept this lsn,
+	 * in this case there is no need to check for existing candidate LSNs
+	 */
+	else if (current_lsn <= slot->data.confirmed_flush)
+	{
+		slot->candidate_restart_valid = current_lsn;
+		slot->candidate_restart_lsn = restart_lsn;
+
+		/* our candidate can directly be used */
+		updated_lsn = true;
+	}
+
+	/*
+	 * Only increase if the previous values have been applied, otherwise we
+	 * might never end up updating if the receiver acks too slowly. A missed
+	 * value here will just cause some extra effort after reconnecting.
+	 */
+	if (slot->candidate_restart_valid == InvalidXLogRecPtr)
+	{
+		slot->candidate_restart_valid = current_lsn;
+		slot->candidate_restart_lsn = restart_lsn;
+		SpinLockRelease(&slot->mutex);
+
+		elog(DEBUG1, "got new restart lsn %X/%X at %X/%X",
+			 LSN_FORMAT_ARGS(restart_lsn),
+			 LSN_FORMAT_ARGS(current_lsn));
+	}
+	else
+	{
+		XLogRecPtr	candidate_restart_lsn;
+		XLogRecPtr	candidate_restart_valid;
+		XLogRecPtr	confirmed_flush;
+
+		candidate_restart_lsn = slot->candidate_restart_lsn;
+		candidate_restart_valid = slot->candidate_restart_valid;
+		confirmed_flush = slot->data.confirmed_flush;
+		SpinLockRelease(&slot->mutex);
+
+		elog(DEBUG1, "failed to increase restart lsn: proposed %X/%X, after %X/%X, current candidate %X/%X, current after %X/%X, flushed up to %X/%X",
+			 LSN_FORMAT_ARGS(restart_lsn),
+			 LSN_FORMAT_ARGS(current_lsn),
+			 LSN_FORMAT_ARGS(candidate_restart_lsn),
+			 LSN_FORMAT_ARGS(candidate_restart_valid),
+			 LSN_FORMAT_ARGS(confirmed_flush));
+	}
+
+	/* candidates are already valid with the current flush position, apply */
+	if (updated_lsn)
+		LogicalConfirmReceivedLocation(slot->data.confirmed_flush);
+}
+
+/*
+ * Handle a consumer's confirmation having received all changes up to lsn.
+ */
+void
+LogicalConfirmReceivedLocation(XLogRecPtr lsn)
+{
+	Assert(lsn != InvalidXLogRecPtr);
+
+	/* Do an unlocked check for candidate_lsn first. */
+	if (MyReplicationSlot->candidate_xmin_lsn != InvalidXLogRecPtr ||
+		MyReplicationSlot->candidate_restart_valid != InvalidXLogRecPtr)
+	{
+		bool		updated_xmin = false;
+		bool		updated_restart = false;
+
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+
+		MyReplicationSlot->data.confirmed_flush = lsn;
+
+		/* if we're past the location required for bumping xmin, do so */
+		if (MyReplicationSlot->candidate_xmin_lsn != InvalidXLogRecPtr &&
+			MyReplicationSlot->candidate_xmin_lsn <= lsn)
+		{
+			/*
+			 * We have to write the changed xmin to disk *before* we change
+			 * the in-memory value, otherwise after a crash we wouldn't know
+			 * that some catalog tuples might have been removed already.
+			 *
+			 * Ensure that by first writing to ->xmin and only update
+			 * ->effective_xmin once the new state is synced to disk. After a
+			 * crash ->effective_xmin is set to ->xmin.
+			 */
+			if (TransactionIdIsValid(MyReplicationSlot->candidate_catalog_xmin) &&
+				MyReplicationSlot->data.catalog_xmin != MyReplicationSlot->candidate_catalog_xmin)
+			{
+				MyReplicationSlot->data.catalog_xmin = MyReplicationSlot->candidate_catalog_xmin;
+				MyReplicationSlot->candidate_catalog_xmin = InvalidTransactionId;
+				MyReplicationSlot->candidate_xmin_lsn = InvalidXLogRecPtr;
+				updated_xmin = true;
+			}
+		}
+
+		if (MyReplicationSlot->candidate_restart_valid != InvalidXLogRecPtr &&
+			MyReplicationSlot->candidate_restart_valid <= lsn)
+		{
+			Assert(MyReplicationSlot->candidate_restart_lsn != InvalidXLogRecPtr);
+
+			MyReplicationSlot->data.restart_lsn = MyReplicationSlot->candidate_restart_lsn;
+			MyReplicationSlot->candidate_restart_lsn = InvalidXLogRecPtr;
+			MyReplicationSlot->candidate_restart_valid = InvalidXLogRecPtr;
+			updated_restart = true;
+		}
+
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		/* first write new xmin to disk, so we know what's up after a crash */
+		if (updated_xmin || updated_restart)
+		{
+			ReplicationSlotMarkDirty();
+			ReplicationSlotSave();
+			elog(DEBUG1, "updated xmin: %u restart: %u", updated_xmin, updated_restart);
+		}
+
+		/*
+		 * Now the new xmin is safely on disk, we can let the global value
+		 * advance. We do not take ProcArrayLock or similar since we only
+		 * advance xmin here and there's not much harm done by a concurrent
+		 * computation missing that.
+		 */
+		if (updated_xmin)
+		{
+			SpinLockAcquire(&MyReplicationSlot->mutex);
+			MyReplicationSlot->effective_catalog_xmin = MyReplicationSlot->data.catalog_xmin;
+			SpinLockRelease(&MyReplicationSlot->mutex);
+
+			ReplicationSlotsComputeRequiredXmin(false);
+			ReplicationSlotsComputeRequiredLSN();
+		}
+	}
+	else
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.confirmed_flush = lsn;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+	}
+}
+
+/*
+ * Clear logical streaming state during (sub)transaction abort.
+ */
+void
+ResetLogicalStreamingState(void)
+{
+	CheckXidAlive = InvalidTransactionId;
+	bsysscan = false;
+}
+
+/*
+ * Report stats for a slot.
+ */
+void
+UpdateDecodingStats(LogicalDecodingContext *ctx)
+{
+	ReorderBuffer *rb = ctx->reorder;
+	PgStat_StatReplSlotEntry repSlotStat;
+
+	/* Nothing to do if we don't have any replication stats to be sent. */
+	if (rb->spillBytes <= 0 && rb->streamBytes <= 0 && rb->totalBytes <= 0)
+		return;
+
+	elog(DEBUG2, "UpdateDecodingStats: updating stats %p %lld %lld %lld %lld %lld %lld %lld %lld",
+		 rb,
+		 (long long) rb->spillTxns,
+		 (long long) rb->spillCount,
+		 (long long) rb->spillBytes,
+		 (long long) rb->streamTxns,
+		 (long long) rb->streamCount,
+		 (long long) rb->streamBytes,
+		 (long long) rb->totalTxns,
+		 (long long) rb->totalBytes);
+
+	namestrcpy(&repSlotStat.slotname, NameStr(ctx->slot->data.name));
+	repSlotStat.spill_txns = rb->spillTxns;
+	repSlotStat.spill_count = rb->spillCount;
+	repSlotStat.spill_bytes = rb->spillBytes;
+	repSlotStat.stream_txns = rb->streamTxns;
+	repSlotStat.stream_count = rb->streamCount;
+	repSlotStat.stream_bytes = rb->streamBytes;
+	repSlotStat.total_txns = rb->totalTxns;
+	repSlotStat.total_bytes = rb->totalBytes;
+
+	pgstat_report_replslot(&repSlotStat);
+
+	rb->spillTxns = 0;
+	rb->spillCount = 0;
+	rb->spillBytes = 0;
+	rb->streamTxns = 0;
+	rb->streamCount = 0;
+	rb->streamBytes = 0;
+	rb->totalTxns = 0;
+	rb->totalBytes = 0;
+}
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
new file mode 100644
index 0000000..1f38c5b
--- /dev/null
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -0,0 +1,417 @@
+/*-------------------------------------------------------------------------
+ *
+ * logicalfuncs.c
+ *
+ *	   Support functions for using logical decoding and management of
+ *	   logical replication slots via SQL.
+ *
+ *
+ * Copyright (c) 2012-2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logicalfuncs.c
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include <unistd.h>
+
+#include "access/xact.h"
+#include "access/xlog_internal.h"
+#include "access/xlogutils.h"
+#include "catalog/pg_type.h"
+#include "fmgr.h"
+#include "funcapi.h"
+#include "mb/pg_wchar.h"
+#include "miscadmin.h"
+#include "nodes/makefuncs.h"
+#include "replication/decode.h"
+#include "replication/logical.h"
+#include "replication/message.h"
+#include "storage/fd.h"
+#include "utils/array.h"
+#include "utils/builtins.h"
+#include "utils/inval.h"
+#include "utils/lsyscache.h"
+#include "utils/memutils.h"
+#include "utils/pg_lsn.h"
+#include "utils/regproc.h"
+#include "utils/resowner.h"
+
+/* private date for writing out data */
+typedef struct DecodingOutputState
+{
+	Tuplestorestate *tupstore;
+	TupleDesc	tupdesc;
+	bool		binary_output;
+	int64		returned_rows;
+} DecodingOutputState;
+
+/*
+ * Prepare for an output plugin write.
+ */
+static void
+LogicalOutputPrepareWrite(LogicalDecodingContext *ctx, XLogRecPtr lsn, TransactionId xid,
+						  bool last_write)
+{
+	resetStringInfo(ctx->out);
+}
+
+/*
+ * Perform output plugin write into tuplestore.
+ */
+static void
+LogicalOutputWrite(LogicalDecodingContext *ctx, XLogRecPtr lsn, TransactionId xid,
+				   bool last_write)
+{
+	Datum		values[3];
+	bool		nulls[3];
+	DecodingOutputState *p;
+
+	/* SQL Datums can only be of a limited length... */
+	if (ctx->out->len > MaxAllocSize - VARHDRSZ)
+		elog(ERROR, "too much output for sql interface");
+
+	p = (DecodingOutputState *) ctx->output_writer_private;
+
+	memset(nulls, 0, sizeof(nulls));
+	values[0] = LSNGetDatum(lsn);
+	values[1] = TransactionIdGetDatum(xid);
+
+	/*
+	 * Assert ctx->out is in database encoding when we're writing textual
+	 * output.
+	 */
+	if (!p->binary_output)
+		Assert(pg_verify_mbstr(GetDatabaseEncoding(),
+							   ctx->out->data, ctx->out->len,
+							   false));
+
+	/* ick, but cstring_to_text_with_len works for bytea perfectly fine */
+	values[2] = PointerGetDatum(cstring_to_text_with_len(ctx->out->data, ctx->out->len));
+
+	tuplestore_putvalues(p->tupstore, p->tupdesc, values, nulls);
+	p->returned_rows++;
+}
+
+static void
+check_permissions(void)
+{
+	if (!superuser() && !has_rolreplication(GetUserId()))
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("must be superuser or replication role to use replication slots")));
+}
+
+/*
+ * Helper function for the various SQL callable logical decoding functions.
+ */
+static Datum
+pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool binary)
+{
+	Name		name;
+	XLogRecPtr	upto_lsn;
+	int32		upto_nchanges;
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	MemoryContext per_query_ctx;
+	MemoryContext oldcontext;
+	XLogRecPtr	end_of_wal;
+	LogicalDecodingContext *ctx;
+	ResourceOwner old_resowner = CurrentResourceOwner;
+	ArrayType  *arr;
+	Size		ndim;
+	List	   *options = NIL;
+	DecodingOutputState *p;
+
+	check_permissions();
+
+	CheckLogicalDecodingRequirements();
+
+	if (PG_ARGISNULL(0))
+		ereport(ERROR,
+				(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
+				 errmsg("slot name must not be null")));
+	name = PG_GETARG_NAME(0);
+
+	if (PG_ARGISNULL(1))
+		upto_lsn = InvalidXLogRecPtr;
+	else
+		upto_lsn = PG_GETARG_LSN(1);
+
+	if (PG_ARGISNULL(2))
+		upto_nchanges = InvalidXLogRecPtr;
+	else
+		upto_nchanges = PG_GETARG_INT32(2);
+
+	if (PG_ARGISNULL(3))
+		ereport(ERROR,
+				(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
+				 errmsg("options array must not be null")));
+	arr = PG_GETARG_ARRAYTYPE_P(3);
+
+	/* check to see if caller supports us returning a tuplestore */
+	if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("set-valued function called in context that cannot accept a set")));
+	if (!(rsinfo->allowedModes & SFRM_Materialize))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("materialize mode required, but it is not allowed in this context")));
+
+	/* state to write output to */
+	p = palloc0(sizeof(DecodingOutputState));
+
+	p->binary_output = binary;
+
+	/* Build a tuple descriptor for our result type */
+	if (get_call_result_type(fcinfo, NULL, &p->tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
+
+	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
+	oldcontext = MemoryContextSwitchTo(per_query_ctx);
+
+	/* Deconstruct options array */
+	ndim = ARR_NDIM(arr);
+	if (ndim > 1)
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("array must be one-dimensional")));
+	}
+	else if (array_contains_nulls(arr))
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("array must not contain nulls")));
+	}
+	else if (ndim == 1)
+	{
+		int			nelems;
+		Datum	   *datum_opts;
+		int			i;
+
+		Assert(ARR_ELEMTYPE(arr) == TEXTOID);
+
+		deconstruct_array(arr, TEXTOID, -1, false, TYPALIGN_INT,
+						  &datum_opts, NULL, &nelems);
+
+		if (nelems % 2 != 0)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("array must have even number of elements")));
+
+		for (i = 0; i < nelems; i += 2)
+		{
+			char	   *name = TextDatumGetCString(datum_opts[i]);
+			char	   *opt = TextDatumGetCString(datum_opts[i + 1]);
+
+			options = lappend(options, makeDefElem(name, (Node *) makeString(opt), -1));
+		}
+	}
+
+	p->tupstore = tuplestore_begin_heap(true, false, work_mem);
+	rsinfo->returnMode = SFRM_Materialize;
+	rsinfo->setResult = p->tupstore;
+	rsinfo->setDesc = p->tupdesc;
+
+	/*
+	 * Compute the current end-of-wal and maintain ThisTimeLineID.
+	 * RecoveryInProgress() will update ThisTimeLineID on promotion.
+	 */
+	if (!RecoveryInProgress())
+		end_of_wal = GetFlushRecPtr();
+	else
+		end_of_wal = GetXLogReplayRecPtr(&ThisTimeLineID);
+
+	ReplicationSlotAcquire(NameStr(*name), true);
+
+	PG_TRY();
+	{
+		/* restart at slot's confirmed_flush */
+		ctx = CreateDecodingContext(InvalidXLogRecPtr,
+									options,
+									false,
+									XL_ROUTINE(.page_read = read_local_xlog_page,
+											   .segment_open = wal_segment_open,
+											   .segment_close = wal_segment_close),
+									LogicalOutputPrepareWrite,
+									LogicalOutputWrite, NULL);
+
+		/*
+		 * After the sanity checks in CreateDecodingContext, make sure the
+		 * restart_lsn is valid.  Avoid "cannot get changes" wording in this
+		 * errmsg because that'd be confusingly ambiguous about no changes
+		 * being available.
+		 */
+		if (XLogRecPtrIsInvalid(MyReplicationSlot->data.restart_lsn))
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("can no longer get changes from replication slot \"%s\"",
+							NameStr(*name)),
+					 errdetail("This slot has never previously reserved WAL, or it has been invalidated.")));
+
+		MemoryContextSwitchTo(oldcontext);
+
+		/*
+		 * Check whether the output plugin writes textual output if that's
+		 * what we need.
+		 */
+		if (!binary &&
+			ctx->options.output_type !=OUTPUT_PLUGIN_TEXTUAL_OUTPUT)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("logical decoding output plugin \"%s\" produces binary output, but function \"%s\" expects textual data",
+							NameStr(MyReplicationSlot->data.plugin),
+							format_procedure(fcinfo->flinfo->fn_oid))));
+
+		ctx->output_writer_private = p;
+
+		/*
+		 * Decoding of WAL must start at restart_lsn so that the entirety of
+		 * xacts that committed after the slot's confirmed_flush can be
+		 * accumulated into reorder buffers.
+		 */
+		XLogBeginRead(ctx->reader, MyReplicationSlot->data.restart_lsn);
+
+		/* invalidate non-timetravel entries */
+		InvalidateSystemCaches();
+
+		/* Decode until we run out of records */
+		while (ctx->reader->EndRecPtr < end_of_wal)
+		{
+			XLogRecord *record;
+			char	   *errm = NULL;
+
+			record = XLogReadRecord(ctx->reader, &errm);
+			if (errm)
+				elog(ERROR, "%s", errm);
+
+			/*
+			 * The {begin_txn,change,commit_txn}_wrapper callbacks above will
+			 * store the description into our tuplestore.
+			 */
+			if (record != NULL)
+				LogicalDecodingProcessRecord(ctx, ctx->reader);
+
+			/* check limits */
+			if (upto_lsn != InvalidXLogRecPtr &&
+				upto_lsn <= ctx->reader->EndRecPtr)
+				break;
+			if (upto_nchanges != 0 &&
+				upto_nchanges <= p->returned_rows)
+				break;
+			CHECK_FOR_INTERRUPTS();
+		}
+
+		tuplestore_donestoring(tupstore);
+
+		/*
+		 * Logical decoding could have clobbered CurrentResourceOwner during
+		 * transaction management, so restore the executor's value.  (This is
+		 * a kluge, but it's not worth cleaning up right now.)
+		 */
+		CurrentResourceOwner = old_resowner;
+
+		/*
+		 * Next time, start where we left off. (Hunting things, the family
+		 * business..)
+		 */
+		if (ctx->reader->EndRecPtr != InvalidXLogRecPtr && confirm)
+		{
+			LogicalConfirmReceivedLocation(ctx->reader->EndRecPtr);
+
+			/*
+			 * If only the confirmed_flush_lsn has changed the slot won't get
+			 * marked as dirty by the above. Callers on the walsender
+			 * interface are expected to keep track of their own progress and
+			 * don't need it written out. But SQL-interface users cannot
+			 * specify their own start positions and it's harder for them to
+			 * keep track of their progress, so we should make more of an
+			 * effort to save it for them.
+			 *
+			 * Dirty the slot so it's written out at the next checkpoint.
+			 * We'll still lose its position on crash, as documented, but it's
+			 * better than always losing the position even on clean restart.
+			 */
+			ReplicationSlotMarkDirty();
+		}
+
+		/* free context, call shutdown callback */
+		FreeDecodingContext(ctx);
+
+		ReplicationSlotRelease();
+		InvalidateSystemCaches();
+	}
+	PG_CATCH();
+	{
+		/* clear all timetravel entries */
+		InvalidateSystemCaches();
+
+		PG_RE_THROW();
+	}
+	PG_END_TRY();
+
+	return (Datum) 0;
+}
+
+/*
+ * SQL function returning the changestream as text, consuming the data.
+ */
+Datum
+pg_logical_slot_get_changes(PG_FUNCTION_ARGS)
+{
+	return pg_logical_slot_get_changes_guts(fcinfo, true, false);
+}
+
+/*
+ * SQL function returning the changestream as text, only peeking ahead.
+ */
+Datum
+pg_logical_slot_peek_changes(PG_FUNCTION_ARGS)
+{
+	return pg_logical_slot_get_changes_guts(fcinfo, false, false);
+}
+
+/*
+ * SQL function returning the changestream in binary, consuming the data.
+ */
+Datum
+pg_logical_slot_get_binary_changes(PG_FUNCTION_ARGS)
+{
+	return pg_logical_slot_get_changes_guts(fcinfo, true, true);
+}
+
+/*
+ * SQL function returning the changestream in binary, only peeking ahead.
+ */
+Datum
+pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS)
+{
+	return pg_logical_slot_get_changes_guts(fcinfo, false, true);
+}
+
+
+/*
+ * SQL function for writing logical decoding message into WAL.
+ */
+Datum
+pg_logical_emit_message_bytea(PG_FUNCTION_ARGS)
+{
+	bool		transactional = PG_GETARG_BOOL(0);
+	char	   *prefix = text_to_cstring(PG_GETARG_TEXT_PP(1));
+	bytea	   *data = PG_GETARG_BYTEA_PP(2);
+	XLogRecPtr	lsn;
+
+	lsn = LogLogicalMessage(prefix, VARDATA_ANY(data), VARSIZE_ANY_EXHDR(data),
+							transactional);
+	PG_RETURN_LSN(lsn);
+}
+
+Datum
+pg_logical_emit_message_text(PG_FUNCTION_ARGS)
+{
+	/* bytea and text are compatible */
+	return pg_logical_emit_message_bytea(fcinfo);
+}
diff --git a/src/backend/replication/logical/message.c b/src/backend/replication/logical/message.c
new file mode 100644
index 0000000..93bd372
--- /dev/null
+++ b/src/backend/replication/logical/message.c
@@ -0,0 +1,88 @@
+/*-------------------------------------------------------------------------
+ *
+ * message.c
+ *	  Generic logical messages.
+ *
+ * Copyright (c) 2013-2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/message.c
+ *
+ * NOTES
+ *
+ * Generic logical messages allow XLOG logging of arbitrary binary blobs that
+ * get passed to the logical decoding plugin. In normal XLOG processing they
+ * are same as NOOP.
+ *
+ * These messages can be either transactional or non-transactional.
+ * Transactional messages are part of current transaction and will be sent to
+ * decoding plugin using in a same way as DML operations.
+ * Non-transactional messages are sent to the plugin at the time when the
+ * logical decoding reads them from XLOG. This also means that transactional
+ * messages won't be delivered if the transaction was rolled back but the
+ * non-transactional one will always be delivered.
+ *
+ * Every message carries prefix to avoid conflicts between different decoding
+ * plugins. The plugin authors must take extra care to use unique prefix,
+ * good options seems to be for example to use the name of the extension.
+ *
+ * ---------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/xact.h"
+#include "miscadmin.h"
+#include "nodes/execnodes.h"
+#include "replication/logical.h"
+#include "replication/message.h"
+#include "utils/memutils.h"
+
+/*
+ * Write logical decoding message into XLog.
+ */
+XLogRecPtr
+LogLogicalMessage(const char *prefix, const char *message, size_t size,
+				  bool transactional)
+{
+	xl_logical_message xlrec;
+
+	/*
+	 * Force xid to be allocated if we're emitting a transactional message.
+	 */
+	if (transactional)
+	{
+		Assert(IsTransactionState());
+		GetCurrentTransactionId();
+	}
+
+	xlrec.dbId = MyDatabaseId;
+	xlrec.transactional = transactional;
+	/* trailing zero is critical; see logicalmsg_desc */
+	xlrec.prefix_size = strlen(prefix) + 1;
+	xlrec.message_size = size;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfLogicalMessage);
+	XLogRegisterData(unconstify(char *, prefix), xlrec.prefix_size);
+	XLogRegisterData(unconstify(char *, message), size);
+
+	/* allow origin filtering */
+	XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
+
+	return XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
+}
+
+/*
+ * Redo is basically just noop for logical decoding messages.
+ */
+void
+logicalmsg_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+		elog(PANIC, "logicalmsg_redo: unknown op code %u", info);
+
+	/* This is only interesting for logical decoding, see decode.c. */
+}
diff --git a/src/backend/replication/logical/origin.c b/src/backend/replication/logical/origin.c
new file mode 100644
index 0000000..6988840
--- /dev/null
+++ b/src/backend/replication/logical/origin.c
@@ -0,0 +1,1574 @@
+/*-------------------------------------------------------------------------
+ *
+ * origin.c
+ *	  Logical replication progress tracking support.
+ *
+ * Copyright (c) 2013-2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/origin.c
+ *
+ * NOTES
+ *
+ * This file provides the following:
+ * * An infrastructure to name nodes in a replication setup
+ * * A facility to efficiently store and persist replication progress in an
+ *	 efficient and durable manner.
+ *
+ * Replication origin consist out of a descriptive, user defined, external
+ * name and a short, thus space efficient, internal 2 byte one. This split
+ * exists because replication origin have to be stored in WAL and shared
+ * memory and long descriptors would be inefficient.  For now only use 2 bytes
+ * for the internal id of a replication origin as it seems unlikely that there
+ * soon will be more than 65k nodes in one replication setup; and using only
+ * two bytes allow us to be more space efficient.
+ *
+ * Replication progress is tracked in a shared memory table
+ * (ReplicationState) that's dumped to disk every checkpoint. Entries
+ * ('slots') in this table are identified by the internal id. That's the case
+ * because it allows to increase replication progress during crash
+ * recovery. To allow doing so we store the original LSN (from the originating
+ * system) of a transaction in the commit record. That allows to recover the
+ * precise replayed state after crash recovery; without requiring synchronous
+ * commits. Allowing logical replication to use asynchronous commit is
+ * generally good for performance, but especially important as it allows a
+ * single threaded replay process to keep up with a source that has multiple
+ * backends generating changes concurrently.  For efficiency and simplicity
+ * reasons a backend can setup one replication origin that's from then used as
+ * the source of changes produced by the backend, until reset again.
+ *
+ * This infrastructure is intended to be used in cooperation with logical
+ * decoding. When replaying from a remote system the configured origin is
+ * provided to output plugins, allowing prevention of replication loops and
+ * other filtering.
+ *
+ * There are several levels of locking at work:
+ *
+ * * To create and drop replication origins an exclusive lock on
+ *	 pg_replication_slot is required for the duration. That allows us to
+ *	 safely and conflict free assign new origins using a dirty snapshot.
+ *
+ * * When creating an in-memory replication progress slot the ReplicationOrigin
+ *	 LWLock has to be held exclusively; when iterating over the replication
+ *	 progress a shared lock has to be held, the same when advancing the
+ *	 replication progress of an individual backend that has not setup as the
+ *	 session's replication origin.
+ *
+ * * When manipulating or looking at the remote_lsn and local_lsn fields of a
+ *	 replication progress slot that slot's lwlock has to be held. That's
+ *	 primarily because we do not assume 8 byte writes (the LSN) is atomic on
+ *	 all our platforms, but it also simplifies memory ordering concerns
+ *	 between the remote and local lsn. We use a lwlock instead of a spinlock
+ *	 so it's less harmful to hold the lock over a WAL write
+ *	 (cf. AdvanceReplicationProgress).
+ *
+ * ---------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include <unistd.h>
+#include <sys/stat.h>
+
+#include "access/genam.h"
+#include "access/htup_details.h"
+#include "access/table.h"
+#include "access/xact.h"
+#include "catalog/catalog.h"
+#include "catalog/indexing.h"
+#include "funcapi.h"
+#include "miscadmin.h"
+#include "nodes/execnodes.h"
+#include "pgstat.h"
+#include "replication/logical.h"
+#include "replication/origin.h"
+#include "storage/condition_variable.h"
+#include "storage/copydir.h"
+#include "storage/fd.h"
+#include "storage/ipc.h"
+#include "storage/lmgr.h"
+#include "utils/builtins.h"
+#include "utils/fmgroids.h"
+#include "utils/pg_lsn.h"
+#include "utils/rel.h"
+#include "utils/snapmgr.h"
+#include "utils/syscache.h"
+
+/*
+ * Replay progress of a single remote node.
+ */
+typedef struct ReplicationState
+{
+	/*
+	 * Local identifier for the remote node.
+	 */
+	RepOriginId roident;
+
+	/*
+	 * Location of the latest commit from the remote side.
+	 */
+	XLogRecPtr	remote_lsn;
+
+	/*
+	 * Remember the local lsn of the commit record so we can XLogFlush() to it
+	 * during a checkpoint so we know the commit record actually is safe on
+	 * disk.
+	 */
+	XLogRecPtr	local_lsn;
+
+	/*
+	 * PID of backend that's acquired slot, or 0 if none.
+	 */
+	int			acquired_by;
+
+	/*
+	 * Condition variable that's signaled when acquired_by changes.
+	 */
+	ConditionVariable origin_cv;
+
+	/*
+	 * Lock protecting remote_lsn and local_lsn.
+	 */
+	LWLock		lock;
+} ReplicationState;
+
+/*
+ * On disk version of ReplicationState.
+ */
+typedef struct ReplicationStateOnDisk
+{
+	RepOriginId roident;
+	XLogRecPtr	remote_lsn;
+} ReplicationStateOnDisk;
+
+
+typedef struct ReplicationStateCtl
+{
+	/* Tranche to use for per-origin LWLocks */
+	int			tranche_id;
+	/* Array of length max_replication_slots */
+	ReplicationState states[FLEXIBLE_ARRAY_MEMBER];
+} ReplicationStateCtl;
+
+/* external variables */
+RepOriginId replorigin_session_origin = InvalidRepOriginId; /* assumed identity */
+XLogRecPtr	replorigin_session_origin_lsn = InvalidXLogRecPtr;
+TimestampTz replorigin_session_origin_timestamp = 0;
+
+/*
+ * Base address into a shared memory array of replication states of size
+ * max_replication_slots.
+ *
+ * XXX: Should we use a separate variable to size this rather than
+ * max_replication_slots?
+ */
+static ReplicationState *replication_states;
+
+/*
+ * Actual shared memory block (replication_states[] is now part of this).
+ */
+static ReplicationStateCtl *replication_states_ctl;
+
+/*
+ * Backend-local, cached element from ReplicationState for use in a backend
+ * replaying remote commits, so we don't have to search ReplicationState for
+ * the backends current RepOriginId.
+ */
+static ReplicationState *session_replication_state = NULL;
+
+/* Magic for on disk files. */
+#define REPLICATION_STATE_MAGIC ((uint32) 0x1257DADE)
+
+static void
+replorigin_check_prerequisites(bool check_slots, bool recoveryOK)
+{
+	if (check_slots && max_replication_slots == 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot query or manipulate replication origin when max_replication_slots = 0")));
+
+	if (!recoveryOK && RecoveryInProgress())
+		ereport(ERROR,
+				(errcode(ERRCODE_READ_ONLY_SQL_TRANSACTION),
+				 errmsg("cannot manipulate replication origins during recovery")));
+
+}
+
+
+/* ---------------------------------------------------------------------------
+ * Functions for working with replication origins themselves.
+ * ---------------------------------------------------------------------------
+ */
+
+/*
+ * Check for a persistent replication origin identified by name.
+ *
+ * Returns InvalidOid if the node isn't known yet and missing_ok is true.
+ */
+RepOriginId
+replorigin_by_name(const char *roname, bool missing_ok)
+{
+	Form_pg_replication_origin ident;
+	Oid			roident = InvalidOid;
+	HeapTuple	tuple;
+	Datum		roname_d;
+
+	roname_d = CStringGetTextDatum(roname);
+
+	tuple = SearchSysCache1(REPLORIGNAME, roname_d);
+	if (HeapTupleIsValid(tuple))
+	{
+		ident = (Form_pg_replication_origin) GETSTRUCT(tuple);
+		roident = ident->roident;
+		ReleaseSysCache(tuple);
+	}
+	else if (!missing_ok)
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_OBJECT),
+				 errmsg("replication origin \"%s\" does not exist",
+						roname)));
+
+	return roident;
+}
+
+/*
+ * Create a replication origin.
+ *
+ * Needs to be called in a transaction.
+ */
+RepOriginId
+replorigin_create(const char *roname)
+{
+	Oid			roident;
+	HeapTuple	tuple = NULL;
+	Relation	rel;
+	Datum		roname_d;
+	SnapshotData SnapshotDirty;
+	SysScanDesc scan;
+	ScanKeyData key;
+
+	roname_d = CStringGetTextDatum(roname);
+
+	Assert(IsTransactionState());
+
+	/*
+	 * We need the numeric replication origin to be 16bit wide, so we cannot
+	 * rely on the normal oid allocation. Instead we simply scan
+	 * pg_replication_origin for the first unused id. That's not particularly
+	 * efficient, but this should be a fairly infrequent operation - we can
+	 * easily spend a bit more code on this when it turns out it needs to be
+	 * faster.
+	 *
+	 * We handle concurrency by taking an exclusive lock (allowing reads!)
+	 * over the table for the duration of the search. Because we use a "dirty
+	 * snapshot" we can read rows that other in-progress sessions have
+	 * written, even though they would be invisible with normal snapshots. Due
+	 * to the exclusive lock there's no danger that new rows can appear while
+	 * we're checking.
+	 */
+	InitDirtySnapshot(SnapshotDirty);
+
+	rel = table_open(ReplicationOriginRelationId, ExclusiveLock);
+
+	for (roident = InvalidOid + 1; roident < PG_UINT16_MAX; roident++)
+	{
+		bool		nulls[Natts_pg_replication_origin];
+		Datum		values[Natts_pg_replication_origin];
+		bool		collides;
+
+		CHECK_FOR_INTERRUPTS();
+
+		ScanKeyInit(&key,
+					Anum_pg_replication_origin_roident,
+					BTEqualStrategyNumber, F_OIDEQ,
+					ObjectIdGetDatum(roident));
+
+		scan = systable_beginscan(rel, ReplicationOriginIdentIndex,
+								  true /* indexOK */ ,
+								  &SnapshotDirty,
+								  1, &key);
+
+		collides = HeapTupleIsValid(systable_getnext(scan));
+
+		systable_endscan(scan);
+
+		if (!collides)
+		{
+			/*
+			 * Ok, found an unused roident, insert the new row and do a CCI,
+			 * so our callers can look it up if they want to.
+			 */
+			memset(&nulls, 0, sizeof(nulls));
+
+			values[Anum_pg_replication_origin_roident - 1] = ObjectIdGetDatum(roident);
+			values[Anum_pg_replication_origin_roname - 1] = roname_d;
+
+			tuple = heap_form_tuple(RelationGetDescr(rel), values, nulls);
+			CatalogTupleInsert(rel, tuple);
+			CommandCounterIncrement();
+			break;
+		}
+	}
+
+	/* now release lock again,	*/
+	table_close(rel, ExclusiveLock);
+
+	if (tuple == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+				 errmsg("could not find free replication origin OID")));
+
+	heap_freetuple(tuple);
+	return roident;
+}
+
+/*
+ * Helper function to drop a replication origin.
+ */
+static void
+replorigin_drop_guts(Relation rel, RepOriginId roident, bool nowait)
+{
+	HeapTuple	tuple;
+	int			i;
+
+	/*
+	 * First, clean up the slot state info, if there is any matching slot.
+	 */
+restart:
+	tuple = NULL;
+	LWLockAcquire(ReplicationOriginLock, LW_EXCLUSIVE);
+
+	for (i = 0; i < max_replication_slots; i++)
+	{
+		ReplicationState *state = &replication_states[i];
+
+		if (state->roident == roident)
+		{
+			/* found our slot, is it busy? */
+			if (state->acquired_by != 0)
+			{
+				ConditionVariable *cv;
+
+				if (nowait)
+					ereport(ERROR,
+							(errcode(ERRCODE_OBJECT_IN_USE),
+							 errmsg("could not drop replication origin with OID %d, in use by PID %d",
+									state->roident,
+									state->acquired_by)));
+
+				/*
+				 * We must wait and then retry.  Since we don't know which CV
+				 * to wait on until here, we can't readily use
+				 * ConditionVariablePrepareToSleep (calling it here would be
+				 * wrong, since we could miss the signal if we did so); just
+				 * use ConditionVariableSleep directly.
+				 */
+				cv = &state->origin_cv;
+
+				LWLockRelease(ReplicationOriginLock);
+
+				ConditionVariableSleep(cv, WAIT_EVENT_REPLICATION_ORIGIN_DROP);
+				goto restart;
+			}
+
+			/* first make a WAL log entry */
+			{
+				xl_replorigin_drop xlrec;
+
+				xlrec.node_id = roident;
+				XLogBeginInsert();
+				XLogRegisterData((char *) (&xlrec), sizeof(xlrec));
+				XLogInsert(RM_REPLORIGIN_ID, XLOG_REPLORIGIN_DROP);
+			}
+
+			/* then clear the in-memory slot */
+			state->roident = InvalidRepOriginId;
+			state->remote_lsn = InvalidXLogRecPtr;
+			state->local_lsn = InvalidXLogRecPtr;
+			break;
+		}
+	}
+	LWLockRelease(ReplicationOriginLock);
+	ConditionVariableCancelSleep();
+
+	/*
+	 * Now, we can delete the catalog entry.
+	 */
+	tuple = SearchSysCache1(REPLORIGIDENT, ObjectIdGetDatum(roident));
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "cache lookup failed for replication origin with oid %u",
+			 roident);
+
+	CatalogTupleDelete(rel, &tuple->t_self);
+	ReleaseSysCache(tuple);
+
+	CommandCounterIncrement();
+}
+
+/*
+ * Drop replication origin (by name).
+ *
+ * Needs to be called in a transaction.
+ */
+void
+replorigin_drop_by_name(const char *name, bool missing_ok, bool nowait)
+{
+	RepOriginId roident;
+	Relation	rel;
+
+	Assert(IsTransactionState());
+
+	/*
+	 * To interlock against concurrent drops, we hold ExclusiveLock on
+	 * pg_replication_origin till xact commit.
+	 *
+	 * XXX We can optimize this by acquiring the lock on a specific origin by
+	 * using LockSharedObject if required. However, for that, we first to
+	 * acquire a lock on ReplicationOriginRelationId, get the origin_id, lock
+	 * the specific origin and then re-check if the origin still exists.
+	 */
+	rel = table_open(ReplicationOriginRelationId, ExclusiveLock);
+
+	roident = replorigin_by_name(name, missing_ok);
+
+	if (OidIsValid(roident))
+		replorigin_drop_guts(rel, roident, nowait);
+
+	/* We keep the lock on pg_replication_origin until commit */
+	table_close(rel, NoLock);
+}
+
+/*
+ * Lookup replication origin via its oid and return the name.
+ *
+ * The external name is palloc'd in the calling context.
+ *
+ * Returns true if the origin is known, false otherwise.
+ */
+bool
+replorigin_by_oid(RepOriginId roident, bool missing_ok, char **roname)
+{
+	HeapTuple	tuple;
+	Form_pg_replication_origin ric;
+
+	Assert(OidIsValid((Oid) roident));
+	Assert(roident != InvalidRepOriginId);
+	Assert(roident != DoNotReplicateId);
+
+	tuple = SearchSysCache1(REPLORIGIDENT,
+							ObjectIdGetDatum((Oid) roident));
+
+	if (HeapTupleIsValid(tuple))
+	{
+		ric = (Form_pg_replication_origin) GETSTRUCT(tuple);
+		*roname = text_to_cstring(&ric->roname);
+		ReleaseSysCache(tuple);
+
+		return true;
+	}
+	else
+	{
+		*roname = NULL;
+
+		if (!missing_ok)
+			ereport(ERROR,
+					(errcode(ERRCODE_UNDEFINED_OBJECT),
+					 errmsg("replication origin with OID %u does not exist",
+							roident)));
+
+		return false;
+	}
+}
+
+
+/* ---------------------------------------------------------------------------
+ * Functions for handling replication progress.
+ * ---------------------------------------------------------------------------
+ */
+
+Size
+ReplicationOriginShmemSize(void)
+{
+	Size		size = 0;
+
+	/*
+	 * XXX: max_replication_slots is arguably the wrong thing to use, as here
+	 * we keep the replay state of *remote* transactions. But for now it seems
+	 * sufficient to reuse it, rather than introduce a separate GUC.
+	 */
+	if (max_replication_slots == 0)
+		return size;
+
+	size = add_size(size, offsetof(ReplicationStateCtl, states));
+
+	size = add_size(size,
+					mul_size(max_replication_slots, sizeof(ReplicationState)));
+	return size;
+}
+
+void
+ReplicationOriginShmemInit(void)
+{
+	bool		found;
+
+	if (max_replication_slots == 0)
+		return;
+
+	replication_states_ctl = (ReplicationStateCtl *)
+		ShmemInitStruct("ReplicationOriginState",
+						ReplicationOriginShmemSize(),
+						&found);
+	replication_states = replication_states_ctl->states;
+
+	if (!found)
+	{
+		int			i;
+
+		MemSet(replication_states_ctl, 0, ReplicationOriginShmemSize());
+
+		replication_states_ctl->tranche_id = LWTRANCHE_REPLICATION_ORIGIN_STATE;
+
+		for (i = 0; i < max_replication_slots; i++)
+		{
+			LWLockInitialize(&replication_states[i].lock,
+							 replication_states_ctl->tranche_id);
+			ConditionVariableInit(&replication_states[i].origin_cv);
+		}
+	}
+}
+
+/* ---------------------------------------------------------------------------
+ * Perform a checkpoint of each replication origin's progress with respect to
+ * the replayed remote_lsn. Make sure that all transactions we refer to in the
+ * checkpoint (local_lsn) are actually on-disk. This might not yet be the case
+ * if the transactions were originally committed asynchronously.
+ *
+ * We store checkpoints in the following format:
+ * +-------+------------------------+------------------+-----+--------+
+ * | MAGIC | ReplicationStateOnDisk | struct Replic... | ... | CRC32C | EOF
+ * +-------+------------------------+------------------+-----+--------+
+ *
+ * So its just the magic, followed by the statically sized
+ * ReplicationStateOnDisk structs. Note that the maximum number of
+ * ReplicationState is determined by max_replication_slots.
+ * ---------------------------------------------------------------------------
+ */
+void
+CheckPointReplicationOrigin(void)
+{
+	const char *tmppath = "pg_logical/replorigin_checkpoint.tmp";
+	const char *path = "pg_logical/replorigin_checkpoint";
+	int			tmpfd;
+	int			i;
+	uint32		magic = REPLICATION_STATE_MAGIC;
+	pg_crc32c	crc;
+
+	if (max_replication_slots == 0)
+		return;
+
+	INIT_CRC32C(crc);
+
+	/* make sure no old temp file is remaining */
+	if (unlink(tmppath) < 0 && errno != ENOENT)
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not remove file \"%s\": %m",
+						tmppath)));
+
+	/*
+	 * no other backend can perform this at the same time; only one checkpoint
+	 * can happen at a time.
+	 */
+	tmpfd = OpenTransientFile(tmppath,
+							  O_CREAT | O_EXCL | O_WRONLY | PG_BINARY);
+	if (tmpfd < 0)
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not create file \"%s\": %m",
+						tmppath)));
+
+	/* write magic */
+	errno = 0;
+	if ((write(tmpfd, &magic, sizeof(magic))) != sizeof(magic))
+	{
+		/* if write didn't set errno, assume problem is no disk space */
+		if (errno == 0)
+			errno = ENOSPC;
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not write to file \"%s\": %m",
+						tmppath)));
+	}
+	COMP_CRC32C(crc, &magic, sizeof(magic));
+
+	/* prevent concurrent creations/drops */
+	LWLockAcquire(ReplicationOriginLock, LW_SHARED);
+
+	/* write actual data */
+	for (i = 0; i < max_replication_slots; i++)
+	{
+		ReplicationStateOnDisk disk_state;
+		ReplicationState *curstate = &replication_states[i];
+		XLogRecPtr	local_lsn;
+
+		if (curstate->roident == InvalidRepOriginId)
+			continue;
+
+		/* zero, to avoid uninitialized padding bytes */
+		memset(&disk_state, 0, sizeof(disk_state));
+
+		LWLockAcquire(&curstate->lock, LW_SHARED);
+
+		disk_state.roident = curstate->roident;
+
+		disk_state.remote_lsn = curstate->remote_lsn;
+		local_lsn = curstate->local_lsn;
+
+		LWLockRelease(&curstate->lock);
+
+		/* make sure we only write out a commit that's persistent */
+		XLogFlush(local_lsn);
+
+		errno = 0;
+		if ((write(tmpfd, &disk_state, sizeof(disk_state))) !=
+			sizeof(disk_state))
+		{
+			/* if write didn't set errno, assume problem is no disk space */
+			if (errno == 0)
+				errno = ENOSPC;
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not write to file \"%s\": %m",
+							tmppath)));
+		}
+
+		COMP_CRC32C(crc, &disk_state, sizeof(disk_state));
+	}
+
+	LWLockRelease(ReplicationOriginLock);
+
+	/* write out the CRC */
+	FIN_CRC32C(crc);
+	errno = 0;
+	if ((write(tmpfd, &crc, sizeof(crc))) != sizeof(crc))
+	{
+		/* if write didn't set errno, assume problem is no disk space */
+		if (errno == 0)
+			errno = ENOSPC;
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not write to file \"%s\": %m",
+						tmppath)));
+	}
+
+	if (CloseTransientFile(tmpfd) != 0)
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m",
+						tmppath)));
+
+	/* fsync, rename to permanent file, fsync file and directory */
+	durable_rename(tmppath, path, PANIC);
+}
+
+/*
+ * Recover replication replay status from checkpoint data saved earlier by
+ * CheckPointReplicationOrigin.
+ *
+ * This only needs to be called at startup and *not* during every checkpoint
+ * read during recovery (e.g. in HS or PITR from a base backup) afterwards. All
+ * state thereafter can be recovered by looking at commit records.
+ */
+void
+StartupReplicationOrigin(void)
+{
+	const char *path = "pg_logical/replorigin_checkpoint";
+	int			fd;
+	int			readBytes;
+	uint32		magic = REPLICATION_STATE_MAGIC;
+	int			last_state = 0;
+	pg_crc32c	file_crc;
+	pg_crc32c	crc;
+
+	/* don't want to overwrite already existing state */
+#ifdef USE_ASSERT_CHECKING
+	static bool already_started = false;
+
+	Assert(!already_started);
+	already_started = true;
+#endif
+
+	if (max_replication_slots == 0)
+		return;
+
+	INIT_CRC32C(crc);
+
+	elog(DEBUG2, "starting up replication origin progress state");
+
+	fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
+
+	/*
+	 * might have had max_replication_slots == 0 last run, or we just brought
+	 * up a standby.
+	 */
+	if (fd < 0 && errno == ENOENT)
+		return;
+	else if (fd < 0)
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not open file \"%s\": %m",
+						path)));
+
+	/* verify magic, that is written even if nothing was active */
+	readBytes = read(fd, &magic, sizeof(magic));
+	if (readBytes != sizeof(magic))
+	{
+		if (readBytes < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m",
+							path)));
+		else
+			ereport(PANIC,
+					(errcode(ERRCODE_DATA_CORRUPTED),
+					 errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sizeof(magic))));
+	}
+	COMP_CRC32C(crc, &magic, sizeof(magic));
+
+	if (magic != REPLICATION_STATE_MAGIC)
+		ereport(PANIC,
+				(errmsg("replication checkpoint has wrong magic %u instead of %u",
+						magic, REPLICATION_STATE_MAGIC)));
+
+	/* we can skip locking here, no other access is possible */
+
+	/* recover individual states, until there are no more to be found */
+	while (true)
+	{
+		ReplicationStateOnDisk disk_state;
+
+		readBytes = read(fd, &disk_state, sizeof(disk_state));
+
+		/* no further data */
+		if (readBytes == sizeof(crc))
+		{
+			/* not pretty, but simple ... */
+			file_crc = *(pg_crc32c *) &disk_state;
+			break;
+		}
+
+		if (readBytes < 0)
+		{
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m",
+							path)));
+		}
+
+		if (readBytes != sizeof(disk_state))
+		{
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sizeof(disk_state))));
+		}
+
+		COMP_CRC32C(crc, &disk_state, sizeof(disk_state));
+
+		if (last_state == max_replication_slots)
+			ereport(PANIC,
+					(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
+					 errmsg("could not find free replication state, increase max_replication_slots")));
+
+		/* copy data to shared memory */
+		replication_states[last_state].roident = disk_state.roident;
+		replication_states[last_state].remote_lsn = disk_state.remote_lsn;
+		last_state++;
+
+		ereport(LOG,
+				(errmsg("recovered replication state of node %u to %X/%X",
+						disk_state.roident,
+						LSN_FORMAT_ARGS(disk_state.remote_lsn))));
+	}
+
+	/* now check checksum */
+	FIN_CRC32C(crc);
+	if (file_crc != crc)
+		ereport(PANIC,
+				(errcode(ERRCODE_DATA_CORRUPTED),
+				 errmsg("replication slot checkpoint has wrong checksum %u, expected %u",
+						crc, file_crc)));
+
+	if (CloseTransientFile(fd) != 0)
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m",
+						path)));
+}
+
+void
+replorigin_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	switch (info)
+	{
+		case XLOG_REPLORIGIN_SET:
+			{
+				xl_replorigin_set *xlrec =
+				(xl_replorigin_set *) XLogRecGetData(record);
+
+				replorigin_advance(xlrec->node_id,
+								   xlrec->remote_lsn, record->EndRecPtr,
+								   xlrec->force /* backward */ ,
+								   false /* WAL log */ );
+				break;
+			}
+		case XLOG_REPLORIGIN_DROP:
+			{
+				xl_replorigin_drop *xlrec;
+				int			i;
+
+				xlrec = (xl_replorigin_drop *) XLogRecGetData(record);
+
+				for (i = 0; i < max_replication_slots; i++)
+				{
+					ReplicationState *state = &replication_states[i];
+
+					/* found our slot */
+					if (state->roident == xlrec->node_id)
+					{
+						/* reset entry */
+						state->roident = InvalidRepOriginId;
+						state->remote_lsn = InvalidXLogRecPtr;
+						state->local_lsn = InvalidXLogRecPtr;
+						break;
+					}
+				}
+				break;
+			}
+		default:
+			elog(PANIC, "replorigin_redo: unknown op code %u", info);
+	}
+}
+
+
+/*
+ * Tell the replication origin progress machinery that a commit from 'node'
+ * that originated at the LSN remote_commit on the remote node was replayed
+ * successfully and that we don't need to do so again. In combination with
+ * setting up replorigin_session_origin_lsn and replorigin_session_origin
+ * that ensures we won't lose knowledge about that after a crash if the
+ * transaction had a persistent effect (think of asynchronous commits).
+ *
+ * local_commit needs to be a local LSN of the commit so that we can make sure
+ * upon a checkpoint that enough WAL has been persisted to disk.
+ *
+ * Needs to be called with a RowExclusiveLock on pg_replication_origin,
+ * unless running in recovery.
+ */
+void
+replorigin_advance(RepOriginId node,
+				   XLogRecPtr remote_commit, XLogRecPtr local_commit,
+				   bool go_backward, bool wal_log)
+{
+	int			i;
+	ReplicationState *replication_state = NULL;
+	ReplicationState *free_state = NULL;
+
+	Assert(node != InvalidRepOriginId);
+
+	/* we don't track DoNotReplicateId */
+	if (node == DoNotReplicateId)
+		return;
+
+	/*
+	 * XXX: For the case where this is called by WAL replay, it'd be more
+	 * efficient to restore into a backend local hashtable and only dump into
+	 * shmem after recovery is finished. Let's wait with implementing that
+	 * till it's shown to be a measurable expense
+	 */
+
+	/* Lock exclusively, as we may have to create a new table entry. */
+	LWLockAcquire(ReplicationOriginLock, LW_EXCLUSIVE);
+
+	/*
+	 * Search for either an existing slot for the origin, or a free one we can
+	 * use.
+	 */
+	for (i = 0; i < max_replication_slots; i++)
+	{
+		ReplicationState *curstate = &replication_states[i];
+
+		/* remember where to insert if necessary */
+		if (curstate->roident == InvalidRepOriginId &&
+			free_state == NULL)
+		{
+			free_state = curstate;
+			continue;
+		}
+
+		/* not our slot */
+		if (curstate->roident != node)
+		{
+			continue;
+		}
+
+		/* ok, found slot */
+		replication_state = curstate;
+
+		LWLockAcquire(&replication_state->lock, LW_EXCLUSIVE);
+
+		/* Make sure it's not used by somebody else */
+		if (replication_state->acquired_by != 0)
+		{
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_IN_USE),
+					 errmsg("replication origin with OID %d is already active for PID %d",
+							replication_state->roident,
+							replication_state->acquired_by)));
+		}
+
+		break;
+	}
+
+	if (replication_state == NULL && free_state == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
+				 errmsg("could not find free replication state slot for replication origin with OID %u",
+						node),
+				 errhint("Increase max_replication_slots and try again.")));
+
+	if (replication_state == NULL)
+	{
+		/* initialize new slot */
+		LWLockAcquire(&free_state->lock, LW_EXCLUSIVE);
+		replication_state = free_state;
+		Assert(replication_state->remote_lsn == InvalidXLogRecPtr);
+		Assert(replication_state->local_lsn == InvalidXLogRecPtr);
+		replication_state->roident = node;
+	}
+
+	Assert(replication_state->roident != InvalidRepOriginId);
+
+	/*
+	 * If somebody "forcefully" sets this slot, WAL log it, so it's durable
+	 * and the standby gets the message. Primarily this will be called during
+	 * WAL replay (of commit records) where no WAL logging is necessary.
+	 */
+	if (wal_log)
+	{
+		xl_replorigin_set xlrec;
+
+		xlrec.remote_lsn = remote_commit;
+		xlrec.node_id = node;
+		xlrec.force = go_backward;
+
+		XLogBeginInsert();
+		XLogRegisterData((char *) (&xlrec), sizeof(xlrec));
+
+		XLogInsert(RM_REPLORIGIN_ID, XLOG_REPLORIGIN_SET);
+	}
+
+	/*
+	 * Due to - harmless - race conditions during a checkpoint we could see
+	 * values here that are older than the ones we already have in memory.
+	 * Don't overwrite those.
+	 */
+	if (go_backward || replication_state->remote_lsn < remote_commit)
+		replication_state->remote_lsn = remote_commit;
+	if (local_commit != InvalidXLogRecPtr &&
+		(go_backward || replication_state->local_lsn < local_commit))
+		replication_state->local_lsn = local_commit;
+	LWLockRelease(&replication_state->lock);
+
+	/*
+	 * Release *after* changing the LSNs, slot isn't acquired and thus could
+	 * otherwise be dropped anytime.
+	 */
+	LWLockRelease(ReplicationOriginLock);
+}
+
+
+XLogRecPtr
+replorigin_get_progress(RepOriginId node, bool flush)
+{
+	int			i;
+	XLogRecPtr	local_lsn = InvalidXLogRecPtr;
+	XLogRecPtr	remote_lsn = InvalidXLogRecPtr;
+
+	/* prevent slots from being concurrently dropped */
+	LWLockAcquire(ReplicationOriginLock, LW_SHARED);
+
+	for (i = 0; i < max_replication_slots; i++)
+	{
+		ReplicationState *state;
+
+		state = &replication_states[i];
+
+		if (state->roident == node)
+		{
+			LWLockAcquire(&state->lock, LW_SHARED);
+
+			remote_lsn = state->remote_lsn;
+			local_lsn = state->local_lsn;
+
+			LWLockRelease(&state->lock);
+
+			break;
+		}
+	}
+
+	LWLockRelease(ReplicationOriginLock);
+
+	if (flush && local_lsn != InvalidXLogRecPtr)
+		XLogFlush(local_lsn);
+
+	return remote_lsn;
+}
+
+/*
+ * Tear down a (possibly) configured session replication origin during process
+ * exit.
+ */
+static void
+ReplicationOriginExitCleanup(int code, Datum arg)
+{
+	ConditionVariable *cv = NULL;
+
+	LWLockAcquire(ReplicationOriginLock, LW_EXCLUSIVE);
+
+	if (session_replication_state != NULL &&
+		session_replication_state->acquired_by == MyProcPid)
+	{
+		cv = &session_replication_state->origin_cv;
+
+		session_replication_state->acquired_by = 0;
+		session_replication_state = NULL;
+	}
+
+	LWLockRelease(ReplicationOriginLock);
+
+	if (cv)
+		ConditionVariableBroadcast(cv);
+}
+
+/*
+ * Setup a replication origin in the shared memory struct if it doesn't
+ * already exists and cache access to the specific ReplicationSlot so the
+ * array doesn't have to be searched when calling
+ * replorigin_session_advance().
+ *
+ * Obviously only one such cached origin can exist per process and the current
+ * cached value can only be set again after the previous value is torn down
+ * with replorigin_session_reset().
+ */
+void
+replorigin_session_setup(RepOriginId node)
+{
+	static bool registered_cleanup;
+	int			i;
+	int			free_slot = -1;
+
+	if (!registered_cleanup)
+	{
+		on_shmem_exit(ReplicationOriginExitCleanup, 0);
+		registered_cleanup = true;
+	}
+
+	Assert(max_replication_slots > 0);
+
+	if (session_replication_state != NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot setup replication origin when one is already setup")));
+
+	/* Lock exclusively, as we may have to create a new table entry. */
+	LWLockAcquire(ReplicationOriginLock, LW_EXCLUSIVE);
+
+	/*
+	 * Search for either an existing slot for the origin, or a free one we can
+	 * use.
+	 */
+	for (i = 0; i < max_replication_slots; i++)
+	{
+		ReplicationState *curstate = &replication_states[i];
+
+		/* remember where to insert if necessary */
+		if (curstate->roident == InvalidRepOriginId &&
+			free_slot == -1)
+		{
+			free_slot = i;
+			continue;
+		}
+
+		/* not our slot */
+		if (curstate->roident != node)
+			continue;
+
+		else if (curstate->acquired_by != 0)
+		{
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_IN_USE),
+					 errmsg("replication origin with OID %d is already active for PID %d",
+							curstate->roident, curstate->acquired_by)));
+		}
+
+		/* ok, found slot */
+		session_replication_state = curstate;
+	}
+
+
+	if (session_replication_state == NULL && free_slot == -1)
+		ereport(ERROR,
+				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
+				 errmsg("could not find free replication state slot for replication origin with OID %u",
+						node),
+				 errhint("Increase max_replication_slots and try again.")));
+	else if (session_replication_state == NULL)
+	{
+		/* initialize new slot */
+		session_replication_state = &replication_states[free_slot];
+		Assert(session_replication_state->remote_lsn == InvalidXLogRecPtr);
+		Assert(session_replication_state->local_lsn == InvalidXLogRecPtr);
+		session_replication_state->roident = node;
+	}
+
+
+	Assert(session_replication_state->roident != InvalidRepOriginId);
+
+	session_replication_state->acquired_by = MyProcPid;
+
+	LWLockRelease(ReplicationOriginLock);
+
+	/* probably this one is pointless */
+	ConditionVariableBroadcast(&session_replication_state->origin_cv);
+}
+
+/*
+ * Reset replay state previously setup in this session.
+ *
+ * This function may only be called if an origin was setup with
+ * replorigin_session_setup().
+ */
+void
+replorigin_session_reset(void)
+{
+	ConditionVariable *cv;
+
+	Assert(max_replication_slots != 0);
+
+	if (session_replication_state == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("no replication origin is configured")));
+
+	LWLockAcquire(ReplicationOriginLock, LW_EXCLUSIVE);
+
+	session_replication_state->acquired_by = 0;
+	cv = &session_replication_state->origin_cv;
+	session_replication_state = NULL;
+
+	LWLockRelease(ReplicationOriginLock);
+
+	ConditionVariableBroadcast(cv);
+}
+
+/*
+ * Do the same work replorigin_advance() does, just on the session's
+ * configured origin.
+ *
+ * This is noticeably cheaper than using replorigin_advance().
+ */
+void
+replorigin_session_advance(XLogRecPtr remote_commit, XLogRecPtr local_commit)
+{
+	Assert(session_replication_state != NULL);
+	Assert(session_replication_state->roident != InvalidRepOriginId);
+
+	LWLockAcquire(&session_replication_state->lock, LW_EXCLUSIVE);
+	if (session_replication_state->local_lsn < local_commit)
+		session_replication_state->local_lsn = local_commit;
+	if (session_replication_state->remote_lsn < remote_commit)
+		session_replication_state->remote_lsn = remote_commit;
+	LWLockRelease(&session_replication_state->lock);
+}
+
+/*
+ * Ask the machinery about the point up to which we successfully replayed
+ * changes from an already setup replication origin.
+ */
+XLogRecPtr
+replorigin_session_get_progress(bool flush)
+{
+	XLogRecPtr	remote_lsn;
+	XLogRecPtr	local_lsn;
+
+	Assert(session_replication_state != NULL);
+
+	LWLockAcquire(&session_replication_state->lock, LW_SHARED);
+	remote_lsn = session_replication_state->remote_lsn;
+	local_lsn = session_replication_state->local_lsn;
+	LWLockRelease(&session_replication_state->lock);
+
+	if (flush && local_lsn != InvalidXLogRecPtr)
+		XLogFlush(local_lsn);
+
+	return remote_lsn;
+}
+
+
+
+/* ---------------------------------------------------------------------------
+ * SQL functions for working with replication origin.
+ *
+ * These mostly should be fairly short wrappers around more generic functions.
+ * ---------------------------------------------------------------------------
+ */
+
+/*
+ * Create replication origin for the passed in name, and return the assigned
+ * oid.
+ */
+Datum
+pg_replication_origin_create(PG_FUNCTION_ARGS)
+{
+	char	   *name;
+	RepOriginId roident;
+
+	replorigin_check_prerequisites(false, false);
+
+	name = text_to_cstring((text *) DatumGetPointer(PG_GETARG_DATUM(0)));
+
+	/* Replication origins "pg_xxx" are reserved for internal use */
+	if (IsReservedName(name))
+		ereport(ERROR,
+				(errcode(ERRCODE_RESERVED_NAME),
+				 errmsg("replication origin name \"%s\" is reserved",
+						name),
+				 errdetail("Origin names starting with \"pg_\" are reserved.")));
+
+	/*
+	 * If built with appropriate switch, whine when regression-testing
+	 * conventions for replication origin names are violated.
+	 */
+#ifdef ENFORCE_REGRESSION_TEST_NAME_RESTRICTIONS
+	if (strncmp(name, "regress_", 8) != 0)
+		elog(WARNING, "replication origins created by regression test cases should have names starting with \"regress_\"");
+#endif
+
+	roident = replorigin_create(name);
+
+	pfree(name);
+
+	PG_RETURN_OID(roident);
+}
+
+/*
+ * Drop replication origin.
+ */
+Datum
+pg_replication_origin_drop(PG_FUNCTION_ARGS)
+{
+	char	   *name;
+
+	replorigin_check_prerequisites(false, false);
+
+	name = text_to_cstring((text *) DatumGetPointer(PG_GETARG_DATUM(0)));
+
+	replorigin_drop_by_name(name, false, true);
+
+	pfree(name);
+
+	PG_RETURN_VOID();
+}
+
+/*
+ * Return oid of a replication origin.
+ */
+Datum
+pg_replication_origin_oid(PG_FUNCTION_ARGS)
+{
+	char	   *name;
+	RepOriginId roident;
+
+	replorigin_check_prerequisites(false, false);
+
+	name = text_to_cstring((text *) DatumGetPointer(PG_GETARG_DATUM(0)));
+	roident = replorigin_by_name(name, true);
+
+	pfree(name);
+
+	if (OidIsValid(roident))
+		PG_RETURN_OID(roident);
+	PG_RETURN_NULL();
+}
+
+/*
+ * Setup a replication origin for this session.
+ */
+Datum
+pg_replication_origin_session_setup(PG_FUNCTION_ARGS)
+{
+	char	   *name;
+	RepOriginId origin;
+
+	replorigin_check_prerequisites(true, false);
+
+	name = text_to_cstring((text *) DatumGetPointer(PG_GETARG_DATUM(0)));
+	origin = replorigin_by_name(name, false);
+	replorigin_session_setup(origin);
+
+	replorigin_session_origin = origin;
+
+	pfree(name);
+
+	PG_RETURN_VOID();
+}
+
+/*
+ * Reset previously setup origin in this session
+ */
+Datum
+pg_replication_origin_session_reset(PG_FUNCTION_ARGS)
+{
+	replorigin_check_prerequisites(true, false);
+
+	replorigin_session_reset();
+
+	replorigin_session_origin = InvalidRepOriginId;
+	replorigin_session_origin_lsn = InvalidXLogRecPtr;
+	replorigin_session_origin_timestamp = 0;
+
+	PG_RETURN_VOID();
+}
+
+/*
+ * Has a replication origin been setup for this session.
+ */
+Datum
+pg_replication_origin_session_is_setup(PG_FUNCTION_ARGS)
+{
+	replorigin_check_prerequisites(false, false);
+
+	PG_RETURN_BOOL(replorigin_session_origin != InvalidRepOriginId);
+}
+
+
+/*
+ * Return the replication progress for origin setup in the current session.
+ *
+ * If 'flush' is set to true it is ensured that the returned value corresponds
+ * to a local transaction that has been flushed. This is useful if asynchronous
+ * commits are used when replaying replicated transactions.
+ */
+Datum
+pg_replication_origin_session_progress(PG_FUNCTION_ARGS)
+{
+	XLogRecPtr	remote_lsn = InvalidXLogRecPtr;
+	bool		flush = PG_GETARG_BOOL(0);
+
+	replorigin_check_prerequisites(true, false);
+
+	if (session_replication_state == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("no replication origin is configured")));
+
+	remote_lsn = replorigin_session_get_progress(flush);
+
+	if (remote_lsn == InvalidXLogRecPtr)
+		PG_RETURN_NULL();
+
+	PG_RETURN_LSN(remote_lsn);
+}
+
+Datum
+pg_replication_origin_xact_setup(PG_FUNCTION_ARGS)
+{
+	XLogRecPtr	location = PG_GETARG_LSN(0);
+
+	replorigin_check_prerequisites(true, false);
+
+	if (session_replication_state == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("no replication origin is configured")));
+
+	replorigin_session_origin_lsn = location;
+	replorigin_session_origin_timestamp = PG_GETARG_TIMESTAMPTZ(1);
+
+	PG_RETURN_VOID();
+}
+
+Datum
+pg_replication_origin_xact_reset(PG_FUNCTION_ARGS)
+{
+	replorigin_check_prerequisites(true, false);
+
+	replorigin_session_origin_lsn = InvalidXLogRecPtr;
+	replorigin_session_origin_timestamp = 0;
+
+	PG_RETURN_VOID();
+}
+
+
+Datum
+pg_replication_origin_advance(PG_FUNCTION_ARGS)
+{
+	text	   *name = PG_GETARG_TEXT_PP(0);
+	XLogRecPtr	remote_commit = PG_GETARG_LSN(1);
+	RepOriginId node;
+
+	replorigin_check_prerequisites(true, false);
+
+	/* lock to prevent the replication origin from vanishing */
+	LockRelationOid(ReplicationOriginRelationId, RowExclusiveLock);
+
+	node = replorigin_by_name(text_to_cstring(name), false);
+
+	/*
+	 * Can't sensibly pass a local commit to be flushed at checkpoint - this
+	 * xact hasn't committed yet. This is why this function should be used to
+	 * set up the initial replication state, but not for replay.
+	 */
+	replorigin_advance(node, remote_commit, InvalidXLogRecPtr,
+					   true /* go backward */ , true /* WAL log */ );
+
+	UnlockRelationOid(ReplicationOriginRelationId, RowExclusiveLock);
+
+	PG_RETURN_VOID();
+}
+
+
+/*
+ * Return the replication progress for an individual replication origin.
+ *
+ * If 'flush' is set to true it is ensured that the returned value corresponds
+ * to a local transaction that has been flushed. This is useful if asynchronous
+ * commits are used when replaying replicated transactions.
+ */
+Datum
+pg_replication_origin_progress(PG_FUNCTION_ARGS)
+{
+	char	   *name;
+	bool		flush;
+	RepOriginId roident;
+	XLogRecPtr	remote_lsn = InvalidXLogRecPtr;
+
+	replorigin_check_prerequisites(true, true);
+
+	name = text_to_cstring((text *) DatumGetPointer(PG_GETARG_DATUM(0)));
+	flush = PG_GETARG_BOOL(1);
+
+	roident = replorigin_by_name(name, false);
+	Assert(OidIsValid(roident));
+
+	remote_lsn = replorigin_get_progress(roident, flush);
+
+	if (remote_lsn == InvalidXLogRecPtr)
+		PG_RETURN_NULL();
+
+	PG_RETURN_LSN(remote_lsn);
+}
+
+
+Datum
+pg_show_replication_origin_status(PG_FUNCTION_ARGS)
+{
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	TupleDesc	tupdesc;
+	Tuplestorestate *tupstore;
+	MemoryContext per_query_ctx;
+	MemoryContext oldcontext;
+	int			i;
+#define REPLICATION_ORIGIN_PROGRESS_COLS 4
+
+	/* we want to return 0 rows if slot is set to zero */
+	replorigin_check_prerequisites(false, true);
+
+	if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("set-valued function called in context that cannot accept a set")));
+	if (!(rsinfo->allowedModes & SFRM_Materialize))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("materialize mode required, but it is not allowed in this context")));
+	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
+
+	if (tupdesc->natts != REPLICATION_ORIGIN_PROGRESS_COLS)
+		elog(ERROR, "wrong function definition");
+
+	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
+	oldcontext = MemoryContextSwitchTo(per_query_ctx);
+
+	tupstore = tuplestore_begin_heap(true, false, work_mem);
+	rsinfo->returnMode = SFRM_Materialize;
+	rsinfo->setResult = tupstore;
+	rsinfo->setDesc = tupdesc;
+
+	MemoryContextSwitchTo(oldcontext);
+
+
+	/* prevent slots from being concurrently dropped */
+	LWLockAcquire(ReplicationOriginLock, LW_SHARED);
+
+	/*
+	 * Iterate through all possible replication_states, display if they are
+	 * filled. Note that we do not take any locks, so slightly corrupted/out
+	 * of date values are a possibility.
+	 */
+	for (i = 0; i < max_replication_slots; i++)
+	{
+		ReplicationState *state;
+		Datum		values[REPLICATION_ORIGIN_PROGRESS_COLS];
+		bool		nulls[REPLICATION_ORIGIN_PROGRESS_COLS];
+		char	   *roname;
+
+		state = &replication_states[i];
+
+		/* unused slot, nothing to display */
+		if (state->roident == InvalidRepOriginId)
+			continue;
+
+		memset(values, 0, sizeof(values));
+		memset(nulls, 1, sizeof(nulls));
+
+		values[0] = ObjectIdGetDatum(state->roident);
+		nulls[0] = false;
+
+		/*
+		 * We're not preventing the origin to be dropped concurrently, so
+		 * silently accept that it might be gone.
+		 */
+		if (replorigin_by_oid(state->roident, true,
+							  &roname))
+		{
+			values[1] = CStringGetTextDatum(roname);
+			nulls[1] = false;
+		}
+
+		LWLockAcquire(&state->lock, LW_SHARED);
+
+		values[2] = LSNGetDatum(state->remote_lsn);
+		nulls[2] = false;
+
+		values[3] = LSNGetDatum(state->local_lsn);
+		nulls[3] = false;
+
+		LWLockRelease(&state->lock);
+
+		tuplestore_putvalues(tupstore, tupdesc, values, nulls);
+	}
+
+	tuplestore_donestoring(tupstore);
+
+	LWLockRelease(ReplicationOriginLock);
+
+#undef REPLICATION_ORIGIN_PROGRESS_COLS
+
+	return (Datum) 0;
+}
diff --git a/src/backend/replication/logical/proto.c b/src/backend/replication/logical/proto.c
new file mode 100644
index 0000000..1cf59e0
--- /dev/null
+++ b/src/backend/replication/logical/proto.c
@@ -0,0 +1,900 @@
+/*-------------------------------------------------------------------------
+ *
+ * proto.c
+ *		logical replication protocol functions
+ *
+ * Copyright (c) 2015-2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *		src/backend/replication/logical/proto.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/sysattr.h"
+#include "catalog/pg_namespace.h"
+#include "catalog/pg_type.h"
+#include "libpq/pqformat.h"
+#include "replication/logicalproto.h"
+#include "utils/lsyscache.h"
+#include "utils/syscache.h"
+
+/*
+ * Protocol message flags.
+ */
+#define LOGICALREP_IS_REPLICA_IDENTITY 1
+
+#define MESSAGE_TRANSACTIONAL (1<<0)
+#define TRUNCATE_CASCADE		(1<<0)
+#define TRUNCATE_RESTART_SEQS	(1<<1)
+
+static void logicalrep_write_attrs(StringInfo out, Relation rel);
+static void logicalrep_write_tuple(StringInfo out, Relation rel,
+								   HeapTuple tuple, bool binary);
+
+static void logicalrep_read_attrs(StringInfo in, LogicalRepRelation *rel);
+static void logicalrep_read_tuple(StringInfo in, LogicalRepTupleData *tuple);
+
+static void logicalrep_write_namespace(StringInfo out, Oid nspid);
+static const char *logicalrep_read_namespace(StringInfo in);
+
+/*
+ * Write BEGIN to the output stream.
+ */
+void
+logicalrep_write_begin(StringInfo out, ReorderBufferTXN *txn)
+{
+	pq_sendbyte(out, LOGICAL_REP_MSG_BEGIN);
+
+	/* fixed fields */
+	pq_sendint64(out, txn->final_lsn);
+	pq_sendint64(out, txn->commit_time);
+	pq_sendint32(out, txn->xid);
+}
+
+/*
+ * Read transaction BEGIN from the stream.
+ */
+void
+logicalrep_read_begin(StringInfo in, LogicalRepBeginData *begin_data)
+{
+	/* read fields */
+	begin_data->final_lsn = pq_getmsgint64(in);
+	if (begin_data->final_lsn == InvalidXLogRecPtr)
+		elog(ERROR, "final_lsn not set in begin message");
+	begin_data->committime = pq_getmsgint64(in);
+	begin_data->xid = pq_getmsgint(in, 4);
+}
+
+
+/*
+ * Write COMMIT to the output stream.
+ */
+void
+logicalrep_write_commit(StringInfo out, ReorderBufferTXN *txn,
+						XLogRecPtr commit_lsn)
+{
+	uint8		flags = 0;
+
+	pq_sendbyte(out, LOGICAL_REP_MSG_COMMIT);
+
+	/* send the flags field (unused for now) */
+	pq_sendbyte(out, flags);
+
+	/* send fields */
+	pq_sendint64(out, commit_lsn);
+	pq_sendint64(out, txn->end_lsn);
+	pq_sendint64(out, txn->commit_time);
+}
+
+/*
+ * Read transaction COMMIT from the stream.
+ */
+void
+logicalrep_read_commit(StringInfo in, LogicalRepCommitData *commit_data)
+{
+	/* read flags (unused for now) */
+	uint8		flags = pq_getmsgbyte(in);
+
+	if (flags != 0)
+		elog(ERROR, "unrecognized flags %u in commit message", flags);
+
+	/* read fields */
+	commit_data->commit_lsn = pq_getmsgint64(in);
+	commit_data->end_lsn = pq_getmsgint64(in);
+	commit_data->committime = pq_getmsgint64(in);
+}
+
+/*
+ * Write ORIGIN to the output stream.
+ */
+void
+logicalrep_write_origin(StringInfo out, const char *origin,
+						XLogRecPtr origin_lsn)
+{
+	pq_sendbyte(out, LOGICAL_REP_MSG_ORIGIN);
+
+	/* fixed fields */
+	pq_sendint64(out, origin_lsn);
+
+	/* origin string */
+	pq_sendstring(out, origin);
+}
+
+/*
+ * Read ORIGIN from the output stream.
+ */
+char *
+logicalrep_read_origin(StringInfo in, XLogRecPtr *origin_lsn)
+{
+	/* fixed fields */
+	*origin_lsn = pq_getmsgint64(in);
+
+	/* return origin */
+	return pstrdup(pq_getmsgstring(in));
+}
+
+/*
+ * Write INSERT to the output stream.
+ */
+void
+logicalrep_write_insert(StringInfo out, TransactionId xid, Relation rel,
+						HeapTuple newtuple, bool binary)
+{
+	pq_sendbyte(out, LOGICAL_REP_MSG_INSERT);
+
+	/* transaction ID (if not valid, we're not streaming) */
+	if (TransactionIdIsValid(xid))
+		pq_sendint32(out, xid);
+
+	/* use Oid as relation identifier */
+	pq_sendint32(out, RelationGetRelid(rel));
+
+	pq_sendbyte(out, 'N');		/* new tuple follows */
+	logicalrep_write_tuple(out, rel, newtuple, binary);
+}
+
+/*
+ * Read INSERT from stream.
+ *
+ * Fills the new tuple.
+ */
+LogicalRepRelId
+logicalrep_read_insert(StringInfo in, LogicalRepTupleData *newtup)
+{
+	char		action;
+	LogicalRepRelId relid;
+
+	/* read the relation id */
+	relid = pq_getmsgint(in, 4);
+
+	action = pq_getmsgbyte(in);
+	if (action != 'N')
+		elog(ERROR, "expected new tuple but got %d",
+			 action);
+
+	logicalrep_read_tuple(in, newtup);
+
+	return relid;
+}
+
+/*
+ * Write UPDATE to the output stream.
+ */
+void
+logicalrep_write_update(StringInfo out, TransactionId xid, Relation rel,
+						HeapTuple oldtuple, HeapTuple newtuple, bool binary)
+{
+	pq_sendbyte(out, LOGICAL_REP_MSG_UPDATE);
+
+	Assert(rel->rd_rel->relreplident == REPLICA_IDENTITY_DEFAULT ||
+		   rel->rd_rel->relreplident == REPLICA_IDENTITY_FULL ||
+		   rel->rd_rel->relreplident == REPLICA_IDENTITY_INDEX);
+
+	/* transaction ID (if not valid, we're not streaming) */
+	if (TransactionIdIsValid(xid))
+		pq_sendint32(out, xid);
+
+	/* use Oid as relation identifier */
+	pq_sendint32(out, RelationGetRelid(rel));
+
+	if (oldtuple != NULL)
+	{
+		if (rel->rd_rel->relreplident == REPLICA_IDENTITY_FULL)
+			pq_sendbyte(out, 'O');	/* old tuple follows */
+		else
+			pq_sendbyte(out, 'K');	/* old key follows */
+		logicalrep_write_tuple(out, rel, oldtuple, binary);
+	}
+
+	pq_sendbyte(out, 'N');		/* new tuple follows */
+	logicalrep_write_tuple(out, rel, newtuple, binary);
+}
+
+/*
+ * Read UPDATE from stream.
+ */
+LogicalRepRelId
+logicalrep_read_update(StringInfo in, bool *has_oldtuple,
+					   LogicalRepTupleData *oldtup,
+					   LogicalRepTupleData *newtup)
+{
+	char		action;
+	LogicalRepRelId relid;
+
+	/* read the relation id */
+	relid = pq_getmsgint(in, 4);
+
+	/* read and verify action */
+	action = pq_getmsgbyte(in);
+	if (action != 'K' && action != 'O' && action != 'N')
+		elog(ERROR, "expected action 'N', 'O' or 'K', got %c",
+			 action);
+
+	/* check for old tuple */
+	if (action == 'K' || action == 'O')
+	{
+		logicalrep_read_tuple(in, oldtup);
+		*has_oldtuple = true;
+
+		action = pq_getmsgbyte(in);
+	}
+	else
+		*has_oldtuple = false;
+
+	/* check for new  tuple */
+	if (action != 'N')
+		elog(ERROR, "expected action 'N', got %c",
+			 action);
+
+	logicalrep_read_tuple(in, newtup);
+
+	return relid;
+}
+
+/*
+ * Write DELETE to the output stream.
+ */
+void
+logicalrep_write_delete(StringInfo out, TransactionId xid, Relation rel,
+						HeapTuple oldtuple, bool binary)
+{
+	Assert(rel->rd_rel->relreplident == REPLICA_IDENTITY_DEFAULT ||
+		   rel->rd_rel->relreplident == REPLICA_IDENTITY_FULL ||
+		   rel->rd_rel->relreplident == REPLICA_IDENTITY_INDEX);
+
+	pq_sendbyte(out, LOGICAL_REP_MSG_DELETE);
+
+	/* transaction ID (if not valid, we're not streaming) */
+	if (TransactionIdIsValid(xid))
+		pq_sendint32(out, xid);
+
+	/* use Oid as relation identifier */
+	pq_sendint32(out, RelationGetRelid(rel));
+
+	if (rel->rd_rel->relreplident == REPLICA_IDENTITY_FULL)
+		pq_sendbyte(out, 'O');	/* old tuple follows */
+	else
+		pq_sendbyte(out, 'K');	/* old key follows */
+
+	logicalrep_write_tuple(out, rel, oldtuple, binary);
+}
+
+/*
+ * Read DELETE from stream.
+ *
+ * Fills the old tuple.
+ */
+LogicalRepRelId
+logicalrep_read_delete(StringInfo in, LogicalRepTupleData *oldtup)
+{
+	char		action;
+	LogicalRepRelId relid;
+
+	/* read the relation id */
+	relid = pq_getmsgint(in, 4);
+
+	/* read and verify action */
+	action = pq_getmsgbyte(in);
+	if (action != 'K' && action != 'O')
+		elog(ERROR, "expected action 'O' or 'K', got %c", action);
+
+	logicalrep_read_tuple(in, oldtup);
+
+	return relid;
+}
+
+/*
+ * Write TRUNCATE to the output stream.
+ */
+void
+logicalrep_write_truncate(StringInfo out,
+						  TransactionId xid,
+						  int nrelids,
+						  Oid relids[],
+						  bool cascade, bool restart_seqs)
+{
+	int			i;
+	uint8		flags = 0;
+
+	pq_sendbyte(out, LOGICAL_REP_MSG_TRUNCATE);
+
+	/* transaction ID (if not valid, we're not streaming) */
+	if (TransactionIdIsValid(xid))
+		pq_sendint32(out, xid);
+
+	pq_sendint32(out, nrelids);
+
+	/* encode and send truncate flags */
+	if (cascade)
+		flags |= TRUNCATE_CASCADE;
+	if (restart_seqs)
+		flags |= TRUNCATE_RESTART_SEQS;
+	pq_sendint8(out, flags);
+
+	for (i = 0; i < nrelids; i++)
+		pq_sendint32(out, relids[i]);
+}
+
+/*
+ * Read TRUNCATE from stream.
+ */
+List *
+logicalrep_read_truncate(StringInfo in,
+						 bool *cascade, bool *restart_seqs)
+{
+	int			i;
+	int			nrelids;
+	List	   *relids = NIL;
+	uint8		flags;
+
+	nrelids = pq_getmsgint(in, 4);
+
+	/* read and decode truncate flags */
+	flags = pq_getmsgint(in, 1);
+	*cascade = (flags & TRUNCATE_CASCADE) > 0;
+	*restart_seqs = (flags & TRUNCATE_RESTART_SEQS) > 0;
+
+	for (i = 0; i < nrelids; i++)
+		relids = lappend_oid(relids, pq_getmsgint(in, 4));
+
+	return relids;
+}
+
+/*
+ * Write MESSAGE to stream
+ */
+void
+logicalrep_write_message(StringInfo out, TransactionId xid, XLogRecPtr lsn,
+						 bool transactional, const char *prefix, Size sz,
+						 const char *message)
+{
+	uint8		flags = 0;
+
+	pq_sendbyte(out, LOGICAL_REP_MSG_MESSAGE);
+
+	/* encode and send message flags */
+	if (transactional)
+		flags |= MESSAGE_TRANSACTIONAL;
+
+	/* transaction ID (if not valid, we're not streaming) */
+	if (TransactionIdIsValid(xid))
+		pq_sendint32(out, xid);
+
+	pq_sendint8(out, flags);
+	pq_sendint64(out, lsn);
+	pq_sendstring(out, prefix);
+	pq_sendint32(out, sz);
+	pq_sendbytes(out, message, sz);
+}
+
+/*
+ * Write relation description to the output stream.
+ */
+void
+logicalrep_write_rel(StringInfo out, TransactionId xid, Relation rel)
+{
+	char	   *relname;
+
+	pq_sendbyte(out, LOGICAL_REP_MSG_RELATION);
+
+	/* transaction ID (if not valid, we're not streaming) */
+	if (TransactionIdIsValid(xid))
+		pq_sendint32(out, xid);
+
+	/* use Oid as relation identifier */
+	pq_sendint32(out, RelationGetRelid(rel));
+
+	/* send qualified relation name */
+	logicalrep_write_namespace(out, RelationGetNamespace(rel));
+	relname = RelationGetRelationName(rel);
+	pq_sendstring(out, relname);
+
+	/* send replica identity */
+	pq_sendbyte(out, rel->rd_rel->relreplident);
+
+	/* send the attribute info */
+	logicalrep_write_attrs(out, rel);
+}
+
+/*
+ * Read the relation info from stream and return as LogicalRepRelation.
+ */
+LogicalRepRelation *
+logicalrep_read_rel(StringInfo in)
+{
+	LogicalRepRelation *rel = palloc(sizeof(LogicalRepRelation));
+
+	rel->remoteid = pq_getmsgint(in, 4);
+
+	/* Read relation name from stream */
+	rel->nspname = pstrdup(logicalrep_read_namespace(in));
+	rel->relname = pstrdup(pq_getmsgstring(in));
+
+	/* Read the replica identity. */
+	rel->replident = pq_getmsgbyte(in);
+
+	/* Get attribute description */
+	logicalrep_read_attrs(in, rel);
+
+	return rel;
+}
+
+/*
+ * Write type info to the output stream.
+ *
+ * This function will always write base type info.
+ */
+void
+logicalrep_write_typ(StringInfo out, TransactionId xid, Oid typoid)
+{
+	Oid			basetypoid = getBaseType(typoid);
+	HeapTuple	tup;
+	Form_pg_type typtup;
+
+	pq_sendbyte(out, LOGICAL_REP_MSG_TYPE);
+
+	/* transaction ID (if not valid, we're not streaming) */
+	if (TransactionIdIsValid(xid))
+		pq_sendint32(out, xid);
+
+	tup = SearchSysCache1(TYPEOID, ObjectIdGetDatum(basetypoid));
+	if (!HeapTupleIsValid(tup))
+		elog(ERROR, "cache lookup failed for type %u", basetypoid);
+	typtup = (Form_pg_type) GETSTRUCT(tup);
+
+	/* use Oid as relation identifier */
+	pq_sendint32(out, typoid);
+
+	/* send qualified type name */
+	logicalrep_write_namespace(out, typtup->typnamespace);
+	pq_sendstring(out, NameStr(typtup->typname));
+
+	ReleaseSysCache(tup);
+}
+
+/*
+ * Read type info from the output stream.
+ */
+void
+logicalrep_read_typ(StringInfo in, LogicalRepTyp *ltyp)
+{
+	ltyp->remoteid = pq_getmsgint(in, 4);
+
+	/* Read type name from stream */
+	ltyp->nspname = pstrdup(logicalrep_read_namespace(in));
+	ltyp->typname = pstrdup(pq_getmsgstring(in));
+}
+
+/*
+ * Write a tuple to the outputstream, in the most efficient format possible.
+ */
+static void
+logicalrep_write_tuple(StringInfo out, Relation rel, HeapTuple tuple, bool binary)
+{
+	TupleDesc	desc;
+	Datum		values[MaxTupleAttributeNumber];
+	bool		isnull[MaxTupleAttributeNumber];
+	int			i;
+	uint16		nliveatts = 0;
+
+	desc = RelationGetDescr(rel);
+
+	for (i = 0; i < desc->natts; i++)
+	{
+		if (TupleDescAttr(desc, i)->attisdropped || TupleDescAttr(desc, i)->attgenerated)
+			continue;
+		nliveatts++;
+	}
+	pq_sendint16(out, nliveatts);
+
+	/* try to allocate enough memory from the get-go */
+	enlargeStringInfo(out, tuple->t_len +
+					  nliveatts * (1 + 4));
+
+	heap_deform_tuple(tuple, desc, values, isnull);
+
+	/* Write the values */
+	for (i = 0; i < desc->natts; i++)
+	{
+		HeapTuple	typtup;
+		Form_pg_type typclass;
+		Form_pg_attribute att = TupleDescAttr(desc, i);
+
+		if (att->attisdropped || att->attgenerated)
+			continue;
+
+		if (isnull[i])
+		{
+			pq_sendbyte(out, LOGICALREP_COLUMN_NULL);
+			continue;
+		}
+
+		if (att->attlen == -1 && VARATT_IS_EXTERNAL_ONDISK(values[i]))
+		{
+			/*
+			 * Unchanged toasted datum.  (Note that we don't promise to detect
+			 * unchanged data in general; this is just a cheap check to avoid
+			 * sending large values unnecessarily.)
+			 */
+			pq_sendbyte(out, LOGICALREP_COLUMN_UNCHANGED);
+			continue;
+		}
+
+		typtup = SearchSysCache1(TYPEOID, ObjectIdGetDatum(att->atttypid));
+		if (!HeapTupleIsValid(typtup))
+			elog(ERROR, "cache lookup failed for type %u", att->atttypid);
+		typclass = (Form_pg_type) GETSTRUCT(typtup);
+
+		/*
+		 * Send in binary if requested and type has suitable send function.
+		 */
+		if (binary && OidIsValid(typclass->typsend))
+		{
+			bytea	   *outputbytes;
+			int			len;
+
+			pq_sendbyte(out, LOGICALREP_COLUMN_BINARY);
+			outputbytes = OidSendFunctionCall(typclass->typsend, values[i]);
+			len = VARSIZE(outputbytes) - VARHDRSZ;
+			pq_sendint(out, len, 4);	/* length */
+			pq_sendbytes(out, VARDATA(outputbytes), len);	/* data */
+			pfree(outputbytes);
+		}
+		else
+		{
+			char	   *outputstr;
+
+			pq_sendbyte(out, LOGICALREP_COLUMN_TEXT);
+			outputstr = OidOutputFunctionCall(typclass->typoutput, values[i]);
+			pq_sendcountedtext(out, outputstr, strlen(outputstr), false);
+			pfree(outputstr);
+		}
+
+		ReleaseSysCache(typtup);
+	}
+}
+
+/*
+ * Read tuple in logical replication format from stream.
+ */
+static void
+logicalrep_read_tuple(StringInfo in, LogicalRepTupleData *tuple)
+{
+	int			i;
+	int			natts;
+
+	/* Get number of attributes */
+	natts = pq_getmsgint(in, 2);
+
+	/* Allocate space for per-column values; zero out unused StringInfoDatas */
+	tuple->colvalues = (StringInfoData *) palloc0(natts * sizeof(StringInfoData));
+	tuple->colstatus = (char *) palloc(natts * sizeof(char));
+	tuple->ncols = natts;
+
+	/* Read the data */
+	for (i = 0; i < natts; i++)
+	{
+		char		kind;
+		int			len;
+		StringInfo	value = &tuple->colvalues[i];
+
+		kind = pq_getmsgbyte(in);
+		tuple->colstatus[i] = kind;
+
+		switch (kind)
+		{
+			case LOGICALREP_COLUMN_NULL:
+				/* nothing more to do */
+				break;
+			case LOGICALREP_COLUMN_UNCHANGED:
+				/* we don't receive the value of an unchanged column */
+				break;
+			case LOGICALREP_COLUMN_TEXT:
+				len = pq_getmsgint(in, 4);	/* read length */
+
+				/* and data */
+				value->data = palloc(len + 1);
+				pq_copymsgbytes(in, value->data, len);
+				value->data[len] = '\0';
+				/* make StringInfo fully valid */
+				value->len = len;
+				value->cursor = 0;
+				value->maxlen = len;
+				break;
+			case LOGICALREP_COLUMN_BINARY:
+				len = pq_getmsgint(in, 4);	/* read length */
+
+				/* and data */
+				value->data = palloc(len + 1);
+				pq_copymsgbytes(in, value->data, len);
+				/* not strictly necessary but per StringInfo practice */
+				value->data[len] = '\0';
+				/* make StringInfo fully valid */
+				value->len = len;
+				value->cursor = 0;
+				value->maxlen = len;
+				break;
+			default:
+				elog(ERROR, "unrecognized data representation type '%c'", kind);
+		}
+	}
+}
+
+/*
+ * Write relation attribute metadata to the stream.
+ */
+static void
+logicalrep_write_attrs(StringInfo out, Relation rel)
+{
+	TupleDesc	desc;
+	int			i;
+	uint16		nliveatts = 0;
+	Bitmapset  *idattrs = NULL;
+	bool		replidentfull;
+
+	desc = RelationGetDescr(rel);
+
+	/* send number of live attributes */
+	for (i = 0; i < desc->natts; i++)
+	{
+		if (TupleDescAttr(desc, i)->attisdropped || TupleDescAttr(desc, i)->attgenerated)
+			continue;
+		nliveatts++;
+	}
+	pq_sendint16(out, nliveatts);
+
+	/* fetch bitmap of REPLICATION IDENTITY attributes */
+	replidentfull = (rel->rd_rel->relreplident == REPLICA_IDENTITY_FULL);
+	if (!replidentfull)
+		idattrs = RelationGetIdentityKeyBitmap(rel);
+
+	/* send the attributes */
+	for (i = 0; i < desc->natts; i++)
+	{
+		Form_pg_attribute att = TupleDescAttr(desc, i);
+		uint8		flags = 0;
+
+		if (att->attisdropped || att->attgenerated)
+			continue;
+
+		/* REPLICA IDENTITY FULL means all columns are sent as part of key. */
+		if (replidentfull ||
+			bms_is_member(att->attnum - FirstLowInvalidHeapAttributeNumber,
+						  idattrs))
+			flags |= LOGICALREP_IS_REPLICA_IDENTITY;
+
+		pq_sendbyte(out, flags);
+
+		/* attribute name */
+		pq_sendstring(out, NameStr(att->attname));
+
+		/* attribute type id */
+		pq_sendint32(out, (int) att->atttypid);
+
+		/* attribute mode */
+		pq_sendint32(out, att->atttypmod);
+	}
+
+	bms_free(idattrs);
+}
+
+/*
+ * Read relation attribute metadata from the stream.
+ */
+static void
+logicalrep_read_attrs(StringInfo in, LogicalRepRelation *rel)
+{
+	int			i;
+	int			natts;
+	char	  **attnames;
+	Oid		   *atttyps;
+	Bitmapset  *attkeys = NULL;
+
+	natts = pq_getmsgint(in, 2);
+	attnames = palloc(natts * sizeof(char *));
+	atttyps = palloc(natts * sizeof(Oid));
+
+	/* read the attributes */
+	for (i = 0; i < natts; i++)
+	{
+		uint8		flags;
+
+		/* Check for replica identity column */
+		flags = pq_getmsgbyte(in);
+		if (flags & LOGICALREP_IS_REPLICA_IDENTITY)
+			attkeys = bms_add_member(attkeys, i);
+
+		/* attribute name */
+		attnames[i] = pstrdup(pq_getmsgstring(in));
+
+		/* attribute type id */
+		atttyps[i] = (Oid) pq_getmsgint(in, 4);
+
+		/* we ignore attribute mode for now */
+		(void) pq_getmsgint(in, 4);
+	}
+
+	rel->attnames = attnames;
+	rel->atttyps = atttyps;
+	rel->attkeys = attkeys;
+	rel->natts = natts;
+}
+
+/*
+ * Write the namespace name or empty string for pg_catalog (to save space).
+ */
+static void
+logicalrep_write_namespace(StringInfo out, Oid nspid)
+{
+	if (nspid == PG_CATALOG_NAMESPACE)
+		pq_sendbyte(out, '\0');
+	else
+	{
+		char	   *nspname = get_namespace_name(nspid);
+
+		if (nspname == NULL)
+			elog(ERROR, "cache lookup failed for namespace %u",
+				 nspid);
+
+		pq_sendstring(out, nspname);
+	}
+}
+
+/*
+ * Read the namespace name while treating empty string as pg_catalog.
+ */
+static const char *
+logicalrep_read_namespace(StringInfo in)
+{
+	const char *nspname = pq_getmsgstring(in);
+
+	if (nspname[0] == '\0')
+		nspname = "pg_catalog";
+
+	return nspname;
+}
+
+/*
+ * Write the information for the start stream message to the output stream.
+ */
+void
+logicalrep_write_stream_start(StringInfo out,
+							  TransactionId xid, bool first_segment)
+{
+	pq_sendbyte(out, LOGICAL_REP_MSG_STREAM_START);
+
+	Assert(TransactionIdIsValid(xid));
+
+	/* transaction ID (we're starting to stream, so must be valid) */
+	pq_sendint32(out, xid);
+
+	/* 1 if this is the first streaming segment for this xid */
+	pq_sendbyte(out, first_segment ? 1 : 0);
+}
+
+/*
+ * Read the information about the start stream message from output stream.
+ */
+TransactionId
+logicalrep_read_stream_start(StringInfo in, bool *first_segment)
+{
+	TransactionId xid;
+
+	Assert(first_segment);
+
+	xid = pq_getmsgint(in, 4);
+	*first_segment = (pq_getmsgbyte(in) == 1);
+
+	return xid;
+}
+
+/*
+ * Write the stop stream message to the output stream.
+ */
+void
+logicalrep_write_stream_stop(StringInfo out)
+{
+	pq_sendbyte(out, LOGICAL_REP_MSG_STREAM_END);
+}
+
+/*
+ * Write STREAM COMMIT to the output stream.
+ */
+void
+logicalrep_write_stream_commit(StringInfo out, ReorderBufferTXN *txn,
+							   XLogRecPtr commit_lsn)
+{
+	uint8		flags = 0;
+
+	pq_sendbyte(out, LOGICAL_REP_MSG_STREAM_COMMIT);
+
+	Assert(TransactionIdIsValid(txn->xid));
+
+	/* transaction ID */
+	pq_sendint32(out, txn->xid);
+
+	/* send the flags field (unused for now) */
+	pq_sendbyte(out, flags);
+
+	/* send fields */
+	pq_sendint64(out, commit_lsn);
+	pq_sendint64(out, txn->end_lsn);
+	pq_sendint64(out, txn->commit_time);
+}
+
+/*
+ * Read STREAM COMMIT from the output stream.
+ */
+TransactionId
+logicalrep_read_stream_commit(StringInfo in, LogicalRepCommitData *commit_data)
+{
+	TransactionId xid;
+	uint8		flags;
+
+	xid = pq_getmsgint(in, 4);
+
+	/* read flags (unused for now) */
+	flags = pq_getmsgbyte(in);
+
+	if (flags != 0)
+		elog(ERROR, "unrecognized flags %u in commit message", flags);
+
+	/* read fields */
+	commit_data->commit_lsn = pq_getmsgint64(in);
+	commit_data->end_lsn = pq_getmsgint64(in);
+	commit_data->committime = pq_getmsgint64(in);
+
+	return xid;
+}
+
+/*
+ * Write STREAM ABORT to the output stream. Note that xid and subxid will be
+ * same for the top-level transaction abort.
+ */
+void
+logicalrep_write_stream_abort(StringInfo out, TransactionId xid,
+							  TransactionId subxid)
+{
+	pq_sendbyte(out, LOGICAL_REP_MSG_STREAM_ABORT);
+
+	Assert(TransactionIdIsValid(xid) && TransactionIdIsValid(subxid));
+
+	/* transaction ID */
+	pq_sendint32(out, xid);
+	pq_sendint32(out, subxid);
+}
+
+/*
+ * Read STREAM ABORT from the output stream.
+ */
+void
+logicalrep_read_stream_abort(StringInfo in, TransactionId *xid,
+							 TransactionId *subxid)
+{
+	Assert(xid && subxid);
+
+	*xid = pq_getmsgint(in, 4);
+	*subxid = pq_getmsgint(in, 4);
+}
diff --git a/src/backend/replication/logical/relation.c b/src/backend/replication/logical/relation.c
new file mode 100644
index 0000000..a5e5bf9
--- /dev/null
+++ b/src/backend/replication/logical/relation.c
@@ -0,0 +1,705 @@
+/*-------------------------------------------------------------------------
+ * relation.c
+ *	   PostgreSQL logical replication relation mapping cache
+ *
+ * Copyright (c) 2016-2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/relation.c
+ *
+ * NOTES
+ *	  Routines in this file mainly have to do with mapping the properties
+ *	  of local replication target relations to the properties of their
+ *	  remote counterpart.
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/table.h"
+#include "catalog/namespace.h"
+#include "catalog/pg_subscription_rel.h"
+#include "executor/executor.h"
+#include "nodes/makefuncs.h"
+#include "replication/logicalrelation.h"
+#include "replication/worker_internal.h"
+#include "utils/inval.h"
+
+
+static MemoryContext LogicalRepRelMapContext = NULL;
+
+static HTAB *LogicalRepRelMap = NULL;
+
+/*
+ * Partition map (LogicalRepPartMap)
+ *
+ * When a partitioned table is used as replication target, replicated
+ * operations are actually performed on its leaf partitions, which requires
+ * the partitions to also be mapped to the remote relation.  Parent's entry
+ * (LogicalRepRelMapEntry) cannot be used as-is for all partitions, because
+ * individual partitions may have different attribute numbers, which means
+ * attribute mappings to remote relation's attributes must be maintained
+ * separately for each partition.
+ */
+static MemoryContext LogicalRepPartMapContext = NULL;
+static HTAB *LogicalRepPartMap = NULL;
+typedef struct LogicalRepPartMapEntry
+{
+	Oid			partoid;		/* LogicalRepPartMap's key */
+	LogicalRepRelMapEntry relmapentry;
+} LogicalRepPartMapEntry;
+
+/*
+ * Relcache invalidation callback for our relation map cache.
+ */
+static void
+logicalrep_relmap_invalidate_cb(Datum arg, Oid reloid)
+{
+	LogicalRepRelMapEntry *entry;
+
+	/* Just to be sure. */
+	if (LogicalRepRelMap == NULL)
+		return;
+
+	if (reloid != InvalidOid)
+	{
+		HASH_SEQ_STATUS status;
+
+		hash_seq_init(&status, LogicalRepRelMap);
+
+		/* TODO, use inverse lookup hashtable? */
+		while ((entry = (LogicalRepRelMapEntry *) hash_seq_search(&status)) != NULL)
+		{
+			if (entry->localreloid == reloid)
+			{
+				entry->localrelvalid = false;
+				hash_seq_term(&status);
+				break;
+			}
+		}
+	}
+	else
+	{
+		/* invalidate all cache entries */
+		HASH_SEQ_STATUS status;
+
+		hash_seq_init(&status, LogicalRepRelMap);
+
+		while ((entry = (LogicalRepRelMapEntry *) hash_seq_search(&status)) != NULL)
+			entry->localrelvalid = false;
+	}
+}
+
+/*
+ * Initialize the relation map cache.
+ */
+static void
+logicalrep_relmap_init(void)
+{
+	HASHCTL		ctl;
+
+	if (!LogicalRepRelMapContext)
+		LogicalRepRelMapContext =
+			AllocSetContextCreate(CacheMemoryContext,
+								  "LogicalRepRelMapContext",
+								  ALLOCSET_DEFAULT_SIZES);
+
+	/* Initialize the relation hash table. */
+	ctl.keysize = sizeof(LogicalRepRelId);
+	ctl.entrysize = sizeof(LogicalRepRelMapEntry);
+	ctl.hcxt = LogicalRepRelMapContext;
+
+	LogicalRepRelMap = hash_create("logicalrep relation map cache", 128, &ctl,
+								   HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
+	/* Watch for invalidation events. */
+	CacheRegisterRelcacheCallback(logicalrep_relmap_invalidate_cb,
+								  (Datum) 0);
+}
+
+/*
+ * Free the entry of a relation map cache.
+ */
+static void
+logicalrep_relmap_free_entry(LogicalRepRelMapEntry *entry)
+{
+	LogicalRepRelation *remoterel;
+
+	remoterel = &entry->remoterel;
+
+	pfree(remoterel->nspname);
+	pfree(remoterel->relname);
+
+	if (remoterel->natts > 0)
+	{
+		int			i;
+
+		for (i = 0; i < remoterel->natts; i++)
+			pfree(remoterel->attnames[i]);
+
+		pfree(remoterel->attnames);
+		pfree(remoterel->atttyps);
+	}
+	bms_free(remoterel->attkeys);
+
+	if (entry->attrmap)
+		free_attrmap(entry->attrmap);
+}
+
+/*
+ * Add new entry or update existing entry in the relation map cache.
+ *
+ * Called when new relation mapping is sent by the publisher to update
+ * our expected view of incoming data from said publisher.
+ */
+void
+logicalrep_relmap_update(LogicalRepRelation *remoterel)
+{
+	MemoryContext oldctx;
+	LogicalRepRelMapEntry *entry;
+	bool		found;
+	int			i;
+
+	if (LogicalRepRelMap == NULL)
+		logicalrep_relmap_init();
+
+	/*
+	 * HASH_ENTER returns the existing entry if present or creates a new one.
+	 */
+	entry = hash_search(LogicalRepRelMap, (void *) &remoterel->remoteid,
+						HASH_ENTER, &found);
+
+	if (found)
+		logicalrep_relmap_free_entry(entry);
+
+	memset(entry, 0, sizeof(LogicalRepRelMapEntry));
+
+	/* Make cached copy of the data */
+	oldctx = MemoryContextSwitchTo(LogicalRepRelMapContext);
+	entry->remoterel.remoteid = remoterel->remoteid;
+	entry->remoterel.nspname = pstrdup(remoterel->nspname);
+	entry->remoterel.relname = pstrdup(remoterel->relname);
+	entry->remoterel.natts = remoterel->natts;
+	entry->remoterel.attnames = palloc(remoterel->natts * sizeof(char *));
+	entry->remoterel.atttyps = palloc(remoterel->natts * sizeof(Oid));
+	for (i = 0; i < remoterel->natts; i++)
+	{
+		entry->remoterel.attnames[i] = pstrdup(remoterel->attnames[i]);
+		entry->remoterel.atttyps[i] = remoterel->atttyps[i];
+	}
+	entry->remoterel.replident = remoterel->replident;
+	entry->remoterel.attkeys = bms_copy(remoterel->attkeys);
+	MemoryContextSwitchTo(oldctx);
+}
+
+/*
+ * Find attribute index in TupleDesc struct by attribute name.
+ *
+ * Returns -1 if not found.
+ */
+static int
+logicalrep_rel_att_by_name(LogicalRepRelation *remoterel, const char *attname)
+{
+	int			i;
+
+	for (i = 0; i < remoterel->natts; i++)
+	{
+		if (strcmp(remoterel->attnames[i], attname) == 0)
+			return i;
+	}
+
+	return -1;
+}
+
+/*
+ * Report error with names of the missing local relation column(s), if any.
+ */
+static void
+logicalrep_report_missing_attrs(LogicalRepRelation *remoterel,
+								Bitmapset *missingatts)
+{
+	if (!bms_is_empty(missingatts))
+	{
+		StringInfoData missingattsbuf;
+		int			missingattcnt = 0;
+		int			i;
+
+		initStringInfo(&missingattsbuf);
+
+		while ((i = bms_first_member(missingatts)) >= 0)
+		{
+			missingattcnt++;
+			if (missingattcnt == 1)
+				appendStringInfo(&missingattsbuf, _("\"%s\""),
+								 remoterel->attnames[i]);
+			else
+				appendStringInfo(&missingattsbuf, _(", \"%s\""),
+								 remoterel->attnames[i]);
+		}
+
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg_plural("logical replication target relation \"%s.%s\" is missing replicated column: %s",
+							   "logical replication target relation \"%s.%s\" is missing replicated columns: %s",
+							   missingattcnt,
+							   remoterel->nspname,
+							   remoterel->relname,
+							   missingattsbuf.data)));
+	}
+}
+
+/*
+ * Check if replica identity matches and mark the updatable flag.
+ *
+ * We allow for stricter replica identity (fewer columns) on subscriber as
+ * that will not stop us from finding unique tuple. IE, if publisher has
+ * identity (id,timestamp) and subscriber just (id) this will not be a
+ * problem, but in the opposite scenario it will.
+ *
+ * We just mark the relation entry as not updatable here if the local
+ * replica identity is found to be insufficient for applying
+ * updates/deletes (inserts don't care!) and leave it to
+ * check_relation_updatable() to throw the actual error if needed.
+ */
+static void
+logicalrep_rel_mark_updatable(LogicalRepRelMapEntry *entry)
+{
+	Bitmapset  *idkey;
+	LogicalRepRelation *remoterel = &entry->remoterel;
+	int			i;
+
+	entry->updatable = true;
+
+	idkey = RelationGetIndexAttrBitmap(entry->localrel,
+									   INDEX_ATTR_BITMAP_IDENTITY_KEY);
+	/* fallback to PK if no replica identity */
+	if (idkey == NULL)
+	{
+		idkey = RelationGetIndexAttrBitmap(entry->localrel,
+										   INDEX_ATTR_BITMAP_PRIMARY_KEY);
+
+		/*
+		 * If no replica identity index and no PK, the published table must
+		 * have replica identity FULL.
+		 */
+		if (idkey == NULL && remoterel->replident != REPLICA_IDENTITY_FULL)
+			entry->updatable = false;
+	}
+
+	i = -1;
+	while ((i = bms_next_member(idkey, i)) >= 0)
+	{
+		int			attnum = i + FirstLowInvalidHeapAttributeNumber;
+
+		if (!AttrNumberIsForUserDefinedAttr(attnum))
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("logical replication target relation \"%s.%s\" uses "
+							"system columns in REPLICA IDENTITY index",
+							remoterel->nspname, remoterel->relname)));
+
+		attnum = AttrNumberGetAttrOffset(attnum);
+
+		if (entry->attrmap->attnums[attnum] < 0 ||
+			!bms_is_member(entry->attrmap->attnums[attnum], remoterel->attkeys))
+		{
+			entry->updatable = false;
+			break;
+		}
+	}
+}
+
+/*
+ * Open the local relation associated with the remote one.
+ *
+ * Rebuilds the Relcache mapping if it was invalidated by local DDL.
+ */
+LogicalRepRelMapEntry *
+logicalrep_rel_open(LogicalRepRelId remoteid, LOCKMODE lockmode)
+{
+	LogicalRepRelMapEntry *entry;
+	bool		found;
+	LogicalRepRelation *remoterel;
+
+	if (LogicalRepRelMap == NULL)
+		logicalrep_relmap_init();
+
+	/* Search for existing entry. */
+	entry = hash_search(LogicalRepRelMap, (void *) &remoteid,
+						HASH_FIND, &found);
+
+	if (!found)
+		elog(ERROR, "no relation map entry for remote relation ID %u",
+			 remoteid);
+
+	remoterel = &entry->remoterel;
+
+	/* Ensure we don't leak a relcache refcount. */
+	if (entry->localrel)
+		elog(ERROR, "remote relation ID %u is already open", remoteid);
+
+	/*
+	 * When opening and locking a relation, pending invalidation messages are
+	 * processed which can invalidate the relation.  Hence, if the entry is
+	 * currently considered valid, try to open the local relation by OID and
+	 * see if invalidation ensues.
+	 */
+	if (entry->localrelvalid)
+	{
+		entry->localrel = try_table_open(entry->localreloid, lockmode);
+		if (!entry->localrel)
+		{
+			/* Table was renamed or dropped. */
+			entry->localrelvalid = false;
+		}
+		else if (!entry->localrelvalid)
+		{
+			/* Note we release the no-longer-useful lock here. */
+			table_close(entry->localrel, lockmode);
+			entry->localrel = NULL;
+		}
+	}
+
+	/*
+	 * If the entry has been marked invalid since we last had lock on it,
+	 * re-open the local relation by name and rebuild all derived data.
+	 */
+	if (!entry->localrelvalid)
+	{
+		Oid			relid;
+		TupleDesc	desc;
+		MemoryContext oldctx;
+		int			i;
+		Bitmapset  *missingatts;
+
+		/* Release the no-longer-useful attrmap, if any. */
+		if (entry->attrmap)
+		{
+			free_attrmap(entry->attrmap);
+			entry->attrmap = NULL;
+		}
+
+		/* Try to find and lock the relation by name. */
+		relid = RangeVarGetRelid(makeRangeVar(remoterel->nspname,
+											  remoterel->relname, -1),
+								 lockmode, true);
+		if (!OidIsValid(relid))
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("logical replication target relation \"%s.%s\" does not exist",
+							remoterel->nspname, remoterel->relname)));
+		entry->localrel = table_open(relid, NoLock);
+		entry->localreloid = relid;
+
+		/* Check for supported relkind. */
+		CheckSubscriptionRelkind(entry->localrel->rd_rel->relkind,
+								 remoterel->nspname, remoterel->relname);
+
+		/*
+		 * Build the mapping of local attribute numbers to remote attribute
+		 * numbers and validate that we don't miss any replicated columns as
+		 * that would result in potentially unwanted data loss.
+		 */
+		desc = RelationGetDescr(entry->localrel);
+		oldctx = MemoryContextSwitchTo(LogicalRepRelMapContext);
+		entry->attrmap = make_attrmap(desc->natts);
+		MemoryContextSwitchTo(oldctx);
+
+		/* check and report missing attrs, if any */
+		missingatts = bms_add_range(NULL, 0, remoterel->natts - 1);
+		for (i = 0; i < desc->natts; i++)
+		{
+			int			attnum;
+			Form_pg_attribute attr = TupleDescAttr(desc, i);
+
+			if (attr->attisdropped || attr->attgenerated)
+			{
+				entry->attrmap->attnums[i] = -1;
+				continue;
+			}
+
+			attnum = logicalrep_rel_att_by_name(remoterel,
+												NameStr(attr->attname));
+
+			entry->attrmap->attnums[i] = attnum;
+			if (attnum >= 0)
+				missingatts = bms_del_member(missingatts, attnum);
+		}
+
+		logicalrep_report_missing_attrs(remoterel, missingatts);
+
+		/* be tidy */
+		bms_free(missingatts);
+
+		/*
+		 * Set if the table's replica identity is enough to apply
+		 * update/delete.
+		 */
+		logicalrep_rel_mark_updatable(entry);
+
+		entry->localrelvalid = true;
+	}
+
+	if (entry->state != SUBREL_STATE_READY)
+		entry->state = GetSubscriptionRelState(MySubscription->oid,
+											   entry->localreloid,
+											   &entry->statelsn);
+
+	return entry;
+}
+
+/*
+ * Close the previously opened logical relation.
+ */
+void
+logicalrep_rel_close(LogicalRepRelMapEntry *rel, LOCKMODE lockmode)
+{
+	table_close(rel->localrel, lockmode);
+	rel->localrel = NULL;
+}
+
+/*
+ * Partition cache: look up partition LogicalRepRelMapEntry's
+ *
+ * Unlike relation map cache, this is keyed by partition OID, not remote
+ * relation OID, because we only have to use this cache in the case where
+ * partitions are not directly mapped to any remote relation, such as when
+ * replication is occurring with one of their ancestors as target.
+ */
+
+/*
+ * Relcache invalidation callback
+ */
+static void
+logicalrep_partmap_invalidate_cb(Datum arg, Oid reloid)
+{
+	LogicalRepPartMapEntry *entry;
+
+	/* Just to be sure. */
+	if (LogicalRepPartMap == NULL)
+		return;
+
+	if (reloid != InvalidOid)
+	{
+		HASH_SEQ_STATUS status;
+
+		hash_seq_init(&status, LogicalRepPartMap);
+
+		/* TODO, use inverse lookup hashtable? */
+		while ((entry = (LogicalRepPartMapEntry *) hash_seq_search(&status)) != NULL)
+		{
+			if (entry->relmapentry.localreloid == reloid)
+			{
+				entry->relmapentry.localrelvalid = false;
+				hash_seq_term(&status);
+				break;
+			}
+		}
+	}
+	else
+	{
+		/* invalidate all cache entries */
+		HASH_SEQ_STATUS status;
+
+		hash_seq_init(&status, LogicalRepPartMap);
+
+		while ((entry = (LogicalRepPartMapEntry *) hash_seq_search(&status)) != NULL)
+			entry->relmapentry.localrelvalid = false;
+	}
+}
+
+/*
+ * Reset the entries in the partition map that refer to remoterel.
+ *
+ * Called when new relation mapping is sent by the publisher to update our
+ * expected view of incoming data from said publisher.
+ *
+ * Note that we don't update the remoterel information in the entry here,
+ * we will update the information in logicalrep_partition_open to avoid
+ * unnecessary work.
+ */
+void
+logicalrep_partmap_reset_relmap(LogicalRepRelation *remoterel)
+{
+	HASH_SEQ_STATUS status;
+	LogicalRepPartMapEntry *part_entry;
+	LogicalRepRelMapEntry *entry;
+
+	if (LogicalRepPartMap == NULL)
+		return;
+
+	hash_seq_init(&status, LogicalRepPartMap);
+	while ((part_entry = (LogicalRepPartMapEntry *) hash_seq_search(&status)) != NULL)
+	{
+		entry = &part_entry->relmapentry;
+
+		if (entry->remoterel.remoteid != remoterel->remoteid)
+			continue;
+
+		logicalrep_relmap_free_entry(entry);
+
+		memset(entry, 0, sizeof(LogicalRepRelMapEntry));
+	}
+}
+
+/*
+ * Initialize the partition map cache.
+ */
+static void
+logicalrep_partmap_init(void)
+{
+	HASHCTL		ctl;
+
+	if (!LogicalRepPartMapContext)
+		LogicalRepPartMapContext =
+			AllocSetContextCreate(CacheMemoryContext,
+								  "LogicalRepPartMapContext",
+								  ALLOCSET_DEFAULT_SIZES);
+
+	/* Initialize the relation hash table. */
+	ctl.keysize = sizeof(Oid);	/* partition OID */
+	ctl.entrysize = sizeof(LogicalRepPartMapEntry);
+	ctl.hcxt = LogicalRepPartMapContext;
+
+	LogicalRepPartMap = hash_create("logicalrep partition map cache", 64, &ctl,
+									HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
+	/* Watch for invalidation events. */
+	CacheRegisterRelcacheCallback(logicalrep_partmap_invalidate_cb,
+								  (Datum) 0);
+}
+
+/*
+ * logicalrep_partition_open
+ *
+ * Returned entry reuses most of the values of the root table's entry, save
+ * the attribute map, which can be different for the partition.  However,
+ * we must physically copy all the data, in case the root table's entry
+ * gets freed/rebuilt.
+ *
+ * Note there's no logicalrep_partition_close, because the caller closes the
+ * component relation.
+ */
+LogicalRepRelMapEntry *
+logicalrep_partition_open(LogicalRepRelMapEntry *root,
+						  Relation partrel, AttrMap *map)
+{
+	LogicalRepRelMapEntry *entry;
+	LogicalRepPartMapEntry *part_entry;
+	LogicalRepRelation *remoterel = &root->remoterel;
+	Oid			partOid = RelationGetRelid(partrel);
+	AttrMap    *attrmap = root->attrmap;
+	bool		found;
+	MemoryContext oldctx;
+
+	if (LogicalRepPartMap == NULL)
+		logicalrep_partmap_init();
+
+	/* Search for existing entry. */
+	part_entry = (LogicalRepPartMapEntry *) hash_search(LogicalRepPartMap,
+														(void *) &partOid,
+														HASH_ENTER, &found);
+
+	entry = &part_entry->relmapentry;
+
+	/*
+	 * We must always overwrite entry->localrel with the latest partition
+	 * Relation pointer, because the Relation pointed to by the old value may
+	 * have been cleared after the caller would have closed the partition
+	 * relation after the last use of this entry.  Note that localrelvalid is
+	 * only updated by the relcache invalidation callback, so it may still be
+	 * true irrespective of whether the Relation pointed to by localrel has
+	 * been cleared or not.
+	 */
+	if (found && entry->localrelvalid)
+	{
+		entry->localrel = partrel;
+		return entry;
+	}
+
+	/* Switch to longer-lived context. */
+	oldctx = MemoryContextSwitchTo(LogicalRepPartMapContext);
+
+	if (!found)
+	{
+		memset(part_entry, 0, sizeof(LogicalRepPartMapEntry));
+		part_entry->partoid = partOid;
+	}
+
+	/* Release the no-longer-useful attrmap, if any. */
+	if (entry->attrmap)
+	{
+		free_attrmap(entry->attrmap);
+		entry->attrmap = NULL;
+	}
+
+	if (!entry->remoterel.remoteid)
+	{
+		int			i;
+
+		/* Remote relation is copied as-is from the root entry. */
+		entry = &part_entry->relmapentry;
+		entry->remoterel.remoteid = remoterel->remoteid;
+		entry->remoterel.nspname = pstrdup(remoterel->nspname);
+		entry->remoterel.relname = pstrdup(remoterel->relname);
+		entry->remoterel.natts = remoterel->natts;
+		entry->remoterel.attnames = palloc(remoterel->natts * sizeof(char *));
+		entry->remoterel.atttyps = palloc(remoterel->natts * sizeof(Oid));
+		for (i = 0; i < remoterel->natts; i++)
+		{
+			entry->remoterel.attnames[i] = pstrdup(remoterel->attnames[i]);
+			entry->remoterel.atttyps[i] = remoterel->atttyps[i];
+		}
+		entry->remoterel.replident = remoterel->replident;
+		entry->remoterel.attkeys = bms_copy(remoterel->attkeys);
+	}
+
+	entry->localrel = partrel;
+	entry->localreloid = partOid;
+
+	/*
+	 * If the partition's attributes don't match the root relation's, we'll
+	 * need to make a new attrmap which maps partition attribute numbers to
+	 * remoterel's, instead of the original which maps root relation's
+	 * attribute numbers to remoterel's.
+	 *
+	 * Note that 'map' which comes from the tuple routing data structure
+	 * contains 1-based attribute numbers (of the parent relation).  However,
+	 * the map in 'entry', a logical replication data structure, contains
+	 * 0-based attribute numbers (of the remote relation).
+	 */
+	if (map)
+	{
+		AttrNumber	attno;
+
+		entry->attrmap = make_attrmap(map->maplen);
+		for (attno = 0; attno < entry->attrmap->maplen; attno++)
+		{
+			AttrNumber	root_attno = map->attnums[attno];
+
+			/* 0 means it's a dropped attribute.  See comments atop AttrMap. */
+			if (root_attno == 0)
+				entry->attrmap->attnums[attno] = -1;
+			else
+				entry->attrmap->attnums[attno] = attrmap->attnums[root_attno - 1];
+		}
+	}
+	else
+	{
+		/* Lacking copy_attmap, do this the hard way. */
+		entry->attrmap = make_attrmap(attrmap->maplen);
+		memcpy(entry->attrmap->attnums, attrmap->attnums,
+			   attrmap->maplen * sizeof(AttrNumber));
+	}
+
+	/* Set if the table's replica identity is enough to apply update/delete. */
+	logicalrep_rel_mark_updatable(entry);
+
+	entry->localrelvalid = true;
+
+	/* state and statelsn are left set to 0. */
+	MemoryContextSwitchTo(oldctx);
+
+	return entry;
+}
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
new file mode 100644
index 0000000..e59d139
--- /dev/null
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -0,0 +1,5156 @@
+/*-------------------------------------------------------------------------
+ *
+ * reorderbuffer.c
+ *	  PostgreSQL logical replay/reorder buffer management
+ *
+ *
+ * Copyright (c) 2012-2021, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/reorderbuffer.c
+ *
+ * NOTES
+ *	  This module gets handed individual pieces of transactions in the order
+ *	  they are written to the WAL and is responsible to reassemble them into
+ *	  toplevel transaction sized pieces. When a transaction is completely
+ *	  reassembled - signaled by reading the transaction commit record - it
+ *	  will then call the output plugin (cf. ReorderBufferCommit()) with the
+ *	  individual changes. The output plugins rely on snapshots built by
+ *	  snapbuild.c which hands them to us.
+ *
+ *	  Transactions and subtransactions/savepoints in postgres are not
+ *	  immediately linked to each other from outside the performing
+ *	  backend. Only at commit/abort (or special xact_assignment records) they
+ *	  are linked together. Which means that we will have to splice together a
+ *	  toplevel transaction from its subtransactions. To do that efficiently we
+ *	  build a binary heap indexed by the smallest current lsn of the individual
+ *	  subtransactions' changestreams. As the individual streams are inherently
+ *	  ordered by LSN - since that is where we build them from - the transaction
+ *	  can easily be reassembled by always using the subtransaction with the
+ *	  smallest current LSN from the heap.
+ *
+ *	  In order to cope with large transactions - which can be several times as
+ *	  big as the available memory - this module supports spooling the contents
+ *	  of a large transactions to disk. When the transaction is replayed the
+ *	  contents of individual (sub-)transactions will be read from disk in
+ *	  chunks.
+ *
+ *	  This module also has to deal with reassembling toast records from the
+ *	  individual chunks stored in WAL. When a new (or initial) version of a
+ *	  tuple is stored in WAL it will always be preceded by the toast chunks
+ *	  emitted for the columns stored out of line. Within a single toplevel
+ *	  transaction there will be no other data carrying records between a row's
+ *	  toast chunks and the row data itself. See ReorderBufferToast* for
+ *	  details.
+ *
+ *	  ReorderBuffer uses two special memory context types - SlabContext for
+ *	  allocations of fixed-length structures (changes and transactions), and
+ *	  GenerationContext for the variable-length transaction data (allocated
+ *	  and freed in groups with similar lifespans).
+ *
+ *	  To limit the amount of memory used by decoded changes, we track memory
+ *	  used at the reorder buffer level (i.e. total amount of memory), and for
+ *	  each transaction. When the total amount of used memory exceeds the
+ *	  limit, the transaction consuming the most memory is then serialized to
+ *	  disk.
+ *
+ *	  Only decoded changes are evicted from memory (spilled to disk), not the
+ *	  transaction records. The number of toplevel transactions is limited,
+ *	  but a transaction with many subtransactions may still consume significant
+ *	  amounts of memory. However, the transaction records are fairly small and
+ *	  are not included in the memory limit.
+ *
+ *	  The current eviction algorithm is very simple - the transaction is
+ *	  picked merely by size, while it might be useful to also consider age
+ *	  (LSN) of the changes for example. With the new Generational memory
+ *	  allocator, evicting the oldest changes would make it more likely the
+ *	  memory gets actually freed.
+ *
+ *	  We still rely on max_changes_in_memory when loading serialized changes
+ *	  back into memory. At that point we can't use the memory limit directly
+ *	  as we load the subxacts independently. One option to deal with this
+ *	  would be to count the subxacts, and allow each to allocate 1/N of the
+ *	  memory limit. That however does not seem very appealing, because with
+ *	  many subtransactions it may easily cause thrashing (short cycles of
+ *	  deserializing and applying very few changes). We probably should give
+ *	  a bit more memory to the oldest subtransactions, because it's likely
+ *	  they are the source for the next sequence of changes.
+ *
+ * -------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <unistd.h>
+#include <sys/stat.h>
+
+#include "access/detoast.h"
+#include "access/heapam.h"
+#include "access/rewriteheap.h"
+#include "access/transam.h"
+#include "access/xact.h"
+#include "access/xlog_internal.h"
+#include "catalog/catalog.h"
+#include "lib/binaryheap.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "replication/logical.h"
+#include "replication/reorderbuffer.h"
+#include "replication/slot.h"
+#include "replication/snapbuild.h"	/* just for SnapBuildSnapDecRefcount */
+#include "storage/bufmgr.h"
+#include "storage/fd.h"
+#include "storage/sinval.h"
+#include "utils/builtins.h"
+#include "utils/combocid.h"
+#include "utils/memdebug.h"
+#include "utils/memutils.h"
+#include "utils/rel.h"
+#include "utils/relfilenodemap.h"
+
+
+/* entry for a hash table we use to map from xid to our transaction state */
+typedef struct ReorderBufferTXNByIdEnt
+{
+	TransactionId xid;
+	ReorderBufferTXN *txn;
+} ReorderBufferTXNByIdEnt;
+
+/* data structures for (relfilenode, ctid) => (cmin, cmax) mapping */
+typedef struct ReorderBufferTupleCidKey
+{
+	RelFileNode relnode;
+	ItemPointerData tid;
+} ReorderBufferTupleCidKey;
+
+typedef struct ReorderBufferTupleCidEnt
+{
+	ReorderBufferTupleCidKey key;
+	CommandId	cmin;
+	CommandId	cmax;
+	CommandId	combocid;		/* just for debugging */
+} ReorderBufferTupleCidEnt;
+
+/* Virtual file descriptor with file offset tracking */
+typedef struct TXNEntryFile
+{
+	File		vfd;			/* -1 when the file is closed */
+	off_t		curOffset;		/* offset for next write or read. Reset to 0
+								 * when vfd is opened. */
+} TXNEntryFile;
+
+/* k-way in-order change iteration support structures */
+typedef struct ReorderBufferIterTXNEntry
+{
+	XLogRecPtr	lsn;
+	ReorderBufferChange *change;
+	ReorderBufferTXN *txn;
+	TXNEntryFile file;
+	XLogSegNo	segno;
+} ReorderBufferIterTXNEntry;
+
+typedef struct ReorderBufferIterTXNState
+{
+	binaryheap *heap;
+	Size		nr_txns;
+	dlist_head	old_change;
+	ReorderBufferIterTXNEntry entries[FLEXIBLE_ARRAY_MEMBER];
+} ReorderBufferIterTXNState;
+
+/* toast datastructures */
+typedef struct ReorderBufferToastEnt
+{
+	Oid			chunk_id;		/* toast_table.chunk_id */
+	int32		last_chunk_seq; /* toast_table.chunk_seq of the last chunk we
+								 * have seen */
+	Size		num_chunks;		/* number of chunks we've already seen */
+	Size		size;			/* combined size of chunks seen */
+	dlist_head	chunks;			/* linked list of chunks */
+	struct varlena *reconstructed;	/* reconstructed varlena now pointed to in
+									 * main tup */
+} ReorderBufferToastEnt;
+
+/* Disk serialization support datastructures */
+typedef struct ReorderBufferDiskChange
+{
+	Size		size;
+	ReorderBufferChange change;
+	/* data follows */
+} ReorderBufferDiskChange;
+
+#define IsSpecInsert(action) \
+( \
+	((action) == REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT) \
+)
+#define IsSpecConfirmOrAbort(action) \
+( \
+	(((action) == REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM) || \
+	((action) == REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT)) \
+)
+#define IsInsertOrUpdate(action) \
+( \
+	(((action) == REORDER_BUFFER_CHANGE_INSERT) || \
+	((action) == REORDER_BUFFER_CHANGE_UPDATE) || \
+	((action) == REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT)) \
+)
+
+/*
+ * Maximum number of changes kept in memory, per transaction. After that,
+ * changes are spooled to disk.
+ *
+ * The current value should be sufficient to decode the entire transaction
+ * without hitting disk in OLTP workloads, while starting to spool to disk in
+ * other workloads reasonably fast.
+ *
+ * At some point in the future it probably makes sense to have a more elaborate
+ * resource management here, but it's not entirely clear what that would look
+ * like.
+ */
+int			logical_decoding_work_mem;
+static const Size max_changes_in_memory = 4096; /* XXX for restore only */
+
+/* ---------------------------------------
+ * primary reorderbuffer support routines
+ * ---------------------------------------
+ */
+static ReorderBufferTXN *ReorderBufferGetTXN(ReorderBuffer *rb);
+static void ReorderBufferReturnTXN(ReorderBuffer *rb, ReorderBufferTXN *txn);
+static ReorderBufferTXN *ReorderBufferTXNByXid(ReorderBuffer *rb,
+											   TransactionId xid, bool create, bool *is_new,
+											   XLogRecPtr lsn, bool create_as_top);
+static void ReorderBufferTransferSnapToParent(ReorderBufferTXN *txn,
+											  ReorderBufferTXN *subtxn);
+
+static void AssertTXNLsnOrder(ReorderBuffer *rb);
+
+/* ---------------------------------------
+ * support functions for lsn-order iterating over the ->changes of a
+ * transaction and its subtransactions
+ *
+ * used for iteration over the k-way heap merge of a transaction and its
+ * subtransactions
+ * ---------------------------------------
+ */
+static void ReorderBufferIterTXNInit(ReorderBuffer *rb, ReorderBufferTXN *txn,
+									 ReorderBufferIterTXNState *volatile *iter_state);
+static ReorderBufferChange *ReorderBufferIterTXNNext(ReorderBuffer *rb, ReorderBufferIterTXNState *state);
+static void ReorderBufferIterTXNFinish(ReorderBuffer *rb,
+									   ReorderBufferIterTXNState *state);
+static void ReorderBufferExecuteInvalidations(uint32 nmsgs, SharedInvalidationMessage *msgs);
+
+/*
+ * ---------------------------------------
+ * Disk serialization support functions
+ * ---------------------------------------
+ */
+static void ReorderBufferCheckMemoryLimit(ReorderBuffer *rb);
+static void ReorderBufferSerializeTXN(ReorderBuffer *rb, ReorderBufferTXN *txn);
+static void ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
+										 int fd, ReorderBufferChange *change);
+static Size ReorderBufferRestoreChanges(ReorderBuffer *rb, ReorderBufferTXN *txn,
+										TXNEntryFile *file, XLogSegNo *segno);
+static void ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
+									   char *change);
+static void ReorderBufferRestoreCleanup(ReorderBuffer *rb, ReorderBufferTXN *txn);
+static void ReorderBufferTruncateTXN(ReorderBuffer *rb, ReorderBufferTXN *txn,
+									 bool txn_prepared);
+static void ReorderBufferCleanupSerializedTXNs(const char *slotname);
+static void ReorderBufferSerializedPath(char *path, ReplicationSlot *slot,
+										TransactionId xid, XLogSegNo segno);
+
+static void ReorderBufferFreeSnap(ReorderBuffer *rb, Snapshot snap);
+static Snapshot ReorderBufferCopySnap(ReorderBuffer *rb, Snapshot orig_snap,
+									  ReorderBufferTXN *txn, CommandId cid);
+
+/*
+ * ---------------------------------------
+ * Streaming support functions
+ * ---------------------------------------
+ */
+static inline bool ReorderBufferCanStream(ReorderBuffer *rb);
+static inline bool ReorderBufferCanStartStreaming(ReorderBuffer *rb);
+static void ReorderBufferStreamTXN(ReorderBuffer *rb, ReorderBufferTXN *txn);
+static void ReorderBufferStreamCommit(ReorderBuffer *rb, ReorderBufferTXN *txn);
+
+/* ---------------------------------------
+ * toast reassembly support
+ * ---------------------------------------
+ */
+static void ReorderBufferToastInitHash(ReorderBuffer *rb, ReorderBufferTXN *txn);
+static void ReorderBufferToastReset(ReorderBuffer *rb, ReorderBufferTXN *txn);
+static void ReorderBufferToastReplace(ReorderBuffer *rb, ReorderBufferTXN *txn,
+									  Relation relation, ReorderBufferChange *change);
+static void ReorderBufferToastAppendChunk(ReorderBuffer *rb, ReorderBufferTXN *txn,
+										  Relation relation, ReorderBufferChange *change);
+
+/*
+ * ---------------------------------------
+ * memory accounting
+ * ---------------------------------------
+ */
+static Size ReorderBufferChangeSize(ReorderBufferChange *change);
+static void ReorderBufferChangeMemoryUpdate(ReorderBuffer *rb,
+											ReorderBufferChange *change,
+											bool addition, Size sz);
+
+/*
+ * Allocate a new ReorderBuffer and clean out any old serialized state from
+ * prior ReorderBuffer instances for the same slot.
+ */
+ReorderBuffer *
+ReorderBufferAllocate(void)
+{
+	ReorderBuffer *buffer;
+	HASHCTL		hash_ctl;
+	MemoryContext new_ctx;
+
+	Assert(MyReplicationSlot != NULL);
+
+	/* allocate memory in own context, to have better accountability */
+	new_ctx = AllocSetContextCreate(CurrentMemoryContext,
+									"ReorderBuffer",
+									ALLOCSET_DEFAULT_SIZES);
+
+	buffer =
+		(ReorderBuffer *) MemoryContextAlloc(new_ctx, sizeof(ReorderBuffer));
+
+	memset(&hash_ctl, 0, sizeof(hash_ctl));
+
+	buffer->context = new_ctx;
+
+	buffer->change_context = SlabContextCreate(new_ctx,
+											   "Change",
+											   SLAB_DEFAULT_BLOCK_SIZE,
+											   sizeof(ReorderBufferChange));
+
+	buffer->txn_context = SlabContextCreate(new_ctx,
+											"TXN",
+											SLAB_DEFAULT_BLOCK_SIZE,
+											sizeof(ReorderBufferTXN));
+
+	buffer->tup_context = GenerationContextCreate(new_ctx,
+												  "Tuples",
+												  SLAB_LARGE_BLOCK_SIZE);
+
+	hash_ctl.keysize = sizeof(TransactionId);
+	hash_ctl.entrysize = sizeof(ReorderBufferTXNByIdEnt);
+	hash_ctl.hcxt = buffer->context;
+
+	buffer->by_txn = hash_create("ReorderBufferByXid", 1000, &hash_ctl,
+								 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
+	buffer->by_txn_last_xid = InvalidTransactionId;
+	buffer->by_txn_last_txn = NULL;
+
+	buffer->outbuf = NULL;
+	buffer->outbufsize = 0;
+	buffer->size = 0;
+
+	buffer->spillTxns = 0;
+	buffer->spillCount = 0;
+	buffer->spillBytes = 0;
+	buffer->streamTxns = 0;
+	buffer->streamCount = 0;
+	buffer->streamBytes = 0;
+	buffer->totalTxns = 0;
+	buffer->totalBytes = 0;
+
+	buffer->current_restart_decoding_lsn = InvalidXLogRecPtr;
+
+	dlist_init(&buffer->toplevel_by_lsn);
+	dlist_init(&buffer->txns_by_base_snapshot_lsn);
+
+	/*
+	 * Ensure there's no stale data from prior uses of this slot, in case some
+	 * prior exit avoided calling ReorderBufferFree. Failure to do this can
+	 * produce duplicated txns, and it's very cheap if there's nothing there.
+	 */
+	ReorderBufferCleanupSerializedTXNs(NameStr(MyReplicationSlot->data.name));
+
+	return buffer;
+}
+
+/*
+ * Free a ReorderBuffer
+ */
+void
+ReorderBufferFree(ReorderBuffer *rb)
+{
+	MemoryContext context = rb->context;
+
+	/*
+	 * We free separately allocated data by entirely scrapping reorderbuffer's
+	 * memory context.
+	 */
+	MemoryContextDelete(context);
+
+	/* Free disk space used by unconsumed reorder buffers */
+	ReorderBufferCleanupSerializedTXNs(NameStr(MyReplicationSlot->data.name));
+}
+
+/*
+ * Get an unused, possibly preallocated, ReorderBufferTXN.
+ */
+static ReorderBufferTXN *
+ReorderBufferGetTXN(ReorderBuffer *rb)
+{
+	ReorderBufferTXN *txn;
+
+	txn = (ReorderBufferTXN *)
+		MemoryContextAlloc(rb->txn_context, sizeof(ReorderBufferTXN));
+
+	memset(txn, 0, sizeof(ReorderBufferTXN));
+
+	dlist_init(&txn->changes);
+	dlist_init(&txn->tuplecids);
+	dlist_init(&txn->subtxns);
+
+	/* InvalidCommandId is not zero, so set it explicitly */
+	txn->command_id = InvalidCommandId;
+	txn->output_plugin_private = NULL;
+
+	return txn;
+}
+
+/*
+ * Free a ReorderBufferTXN.
+ */
+static void
+ReorderBufferReturnTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	/* clean the lookup cache if we were cached (quite likely) */
+	if (rb->by_txn_last_xid == txn->xid)
+	{
+		rb->by_txn_last_xid = InvalidTransactionId;
+		rb->by_txn_last_txn = NULL;
+	}
+
+	/* free data that's contained */
+
+	if (txn->gid != NULL)
+	{
+		pfree(txn->gid);
+		txn->gid = NULL;
+	}
+
+	if (txn->tuplecid_hash != NULL)
+	{
+		hash_destroy(txn->tuplecid_hash);
+		txn->tuplecid_hash = NULL;
+	}
+
+	if (txn->invalidations)
+	{
+		pfree(txn->invalidations);
+		txn->invalidations = NULL;
+	}
+
+	/* Reset the toast hash */
+	ReorderBufferToastReset(rb, txn);
+
+	pfree(txn);
+}
+
+/*
+ * Get a fresh ReorderBufferChange.
+ */
+ReorderBufferChange *
+ReorderBufferGetChange(ReorderBuffer *rb)
+{
+	ReorderBufferChange *change;
+
+	change = (ReorderBufferChange *)
+		MemoryContextAlloc(rb->change_context, sizeof(ReorderBufferChange));
+
+	memset(change, 0, sizeof(ReorderBufferChange));
+	return change;
+}
+
+/*
+ * Free a ReorderBufferChange and update memory accounting, if requested.
+ */
+void
+ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change,
+						  bool upd_mem)
+{
+	/* update memory accounting info */
+	if (upd_mem)
+		ReorderBufferChangeMemoryUpdate(rb, change, false,
+										ReorderBufferChangeSize(change));
+
+	/* free contained data */
+	switch (change->action)
+	{
+		case REORDER_BUFFER_CHANGE_INSERT:
+		case REORDER_BUFFER_CHANGE_UPDATE:
+		case REORDER_BUFFER_CHANGE_DELETE:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
+			if (change->data.tp.newtuple)
+			{
+				ReorderBufferReturnTupleBuf(rb, change->data.tp.newtuple);
+				change->data.tp.newtuple = NULL;
+			}
+
+			if (change->data.tp.oldtuple)
+			{
+				ReorderBufferReturnTupleBuf(rb, change->data.tp.oldtuple);
+				change->data.tp.oldtuple = NULL;
+			}
+			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			if (change->data.msg.prefix != NULL)
+				pfree(change->data.msg.prefix);
+			change->data.msg.prefix = NULL;
+			if (change->data.msg.message != NULL)
+				pfree(change->data.msg.message);
+			change->data.msg.message = NULL;
+			break;
+		case REORDER_BUFFER_CHANGE_INVALIDATION:
+			if (change->data.inval.invalidations)
+				pfree(change->data.inval.invalidations);
+			change->data.inval.invalidations = NULL;
+			break;
+		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
+			if (change->data.snapshot)
+			{
+				ReorderBufferFreeSnap(rb, change->data.snapshot);
+				change->data.snapshot = NULL;
+			}
+			break;
+			/* no data in addition to the struct itself */
+		case REORDER_BUFFER_CHANGE_TRUNCATE:
+			if (change->data.truncate.relids != NULL)
+			{
+				ReorderBufferReturnRelids(rb, change->data.truncate.relids);
+				change->data.truncate.relids = NULL;
+			}
+			break;
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
+		case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
+		case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
+			break;
+	}
+
+	pfree(change);
+}
+
+/*
+ * Get a fresh ReorderBufferTupleBuf fitting at least a tuple of size
+ * tuple_len (excluding header overhead).
+ */
+ReorderBufferTupleBuf *
+ReorderBufferGetTupleBuf(ReorderBuffer *rb, Size tuple_len)
+{
+	ReorderBufferTupleBuf *tuple;
+	Size		alloc_len;
+
+	alloc_len = tuple_len + SizeofHeapTupleHeader;
+
+	tuple = (ReorderBufferTupleBuf *)
+		MemoryContextAlloc(rb->tup_context,
+						   sizeof(ReorderBufferTupleBuf) +
+						   MAXIMUM_ALIGNOF + alloc_len);
+	tuple->alloc_tuple_size = alloc_len;
+	tuple->tuple.t_data = ReorderBufferTupleBufData(tuple);
+
+	return tuple;
+}
+
+/*
+ * Free a ReorderBufferTupleBuf.
+ */
+void
+ReorderBufferReturnTupleBuf(ReorderBuffer *rb, ReorderBufferTupleBuf *tuple)
+{
+	pfree(tuple);
+}
+
+/*
+ * Get an array for relids of truncated relations.
+ *
+ * We use the global memory context (for the whole reorder buffer), because
+ * none of the existing ones seems like a good match (some are SLAB, so we
+ * can't use those, and tup_context is meant for tuple data, not relids). We
+ * could add yet another context, but it seems like an overkill - TRUNCATE is
+ * not particularly common operation, so it does not seem worth it.
+ */
+Oid *
+ReorderBufferGetRelids(ReorderBuffer *rb, int nrelids)
+{
+	Oid		   *relids;
+	Size		alloc_len;
+
+	alloc_len = sizeof(Oid) * nrelids;
+
+	relids = (Oid *) MemoryContextAlloc(rb->context, alloc_len);
+
+	return relids;
+}
+
+/*
+ * Free an array of relids.
+ */
+void
+ReorderBufferReturnRelids(ReorderBuffer *rb, Oid *relids)
+{
+	pfree(relids);
+}
+
+/*
+ * Return the ReorderBufferTXN from the given buffer, specified by Xid.
+ * If create is true, and a transaction doesn't already exist, create it
+ * (with the given LSN, and as top transaction if that's specified);
+ * when this happens, is_new is set to true.
+ */
+static ReorderBufferTXN *
+ReorderBufferTXNByXid(ReorderBuffer *rb, TransactionId xid, bool create,
+					  bool *is_new, XLogRecPtr lsn, bool create_as_top)
+{
+	ReorderBufferTXN *txn;
+	ReorderBufferTXNByIdEnt *ent;
+	bool		found;
+
+	Assert(TransactionIdIsValid(xid));
+
+	/*
+	 * Check the one-entry lookup cache first
+	 */
+	if (TransactionIdIsValid(rb->by_txn_last_xid) &&
+		rb->by_txn_last_xid == xid)
+	{
+		txn = rb->by_txn_last_txn;
+
+		if (txn != NULL)
+		{
+			/* found it, and it's valid */
+			if (is_new)
+				*is_new = false;
+			return txn;
+		}
+
+		/*
+		 * cached as non-existent, and asked not to create? Then nothing else
+		 * to do.
+		 */
+		if (!create)
+			return NULL;
+		/* otherwise fall through to create it */
+	}
+
+	/*
+	 * If the cache wasn't hit or it yielded a "does-not-exist" and we want
+	 * to create an entry.
+	 */
+
+	/* search the lookup table */
+	ent = (ReorderBufferTXNByIdEnt *)
+		hash_search(rb->by_txn,
+					(void *) &xid,
+					create ? HASH_ENTER : HASH_FIND,
+					&found);
+	if (found)
+		txn = ent->txn;
+	else if (create)
+	{
+		/* initialize the new entry, if creation was requested */
+		Assert(ent != NULL);
+		Assert(lsn != InvalidXLogRecPtr);
+
+		ent->txn = ReorderBufferGetTXN(rb);
+		ent->txn->xid = xid;
+		txn = ent->txn;
+		txn->first_lsn = lsn;
+		txn->restart_decoding_lsn = rb->current_restart_decoding_lsn;
+
+		if (create_as_top)
+		{
+			dlist_push_tail(&rb->toplevel_by_lsn, &txn->node);
+			AssertTXNLsnOrder(rb);
+		}
+	}
+	else
+		txn = NULL;				/* not found and not asked to create */
+
+	/* update cache */
+	rb->by_txn_last_xid = xid;
+	rb->by_txn_last_txn = txn;
+
+	if (is_new)
+		*is_new = !found;
+
+	Assert(!create || txn != NULL);
+	return txn;
+}
+
+/*
+ * Record the partial change for the streaming of in-progress transactions.  We
+ * can stream only complete changes so if we have a partial change like toast
+ * table insert or speculative insert then we mark such a 'txn' so that it
+ * can't be streamed.  We also ensure that if the changes in such a 'txn' are
+ * above logical_decoding_work_mem threshold then we stream them as soon as we
+ * have a complete change.
+ */
+static void
+ReorderBufferProcessPartialChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
+								  ReorderBufferChange *change,
+								  bool toast_insert)
+{
+	ReorderBufferTXN *toptxn;
+
+	/*
+	 * The partial changes need to be processed only while streaming
+	 * in-progress transactions.
+	 */
+	if (!ReorderBufferCanStream(rb))
+		return;
+
+	/* Get the top transaction. */
+	if (txn->toptxn != NULL)
+		toptxn = txn->toptxn;
+	else
+		toptxn = txn;
+
+	/*
+	 * Indicate a partial change for toast inserts.  The change will be
+	 * considered as complete once we get the insert or update on the main
+	 * table and we are sure that the pending toast chunks are not required
+	 * anymore.
+	 *
+	 * If we allow streaming when there are pending toast chunks then such
+	 * chunks won't be released till the insert (multi_insert) is complete and
+	 * we expect the txn to have streamed all changes after streaming.  This
+	 * restriction is mainly to ensure the correctness of streamed
+	 * transactions and it doesn't seem worth uplifting such a restriction
+	 * just to allow this case because anyway we will stream the transaction
+	 * once such an insert is complete.
+	 */
+	if (toast_insert)
+		toptxn->txn_flags |= RBTXN_HAS_PARTIAL_CHANGE;
+	else if (rbtxn_has_partial_change(toptxn) &&
+			 IsInsertOrUpdate(change->action) &&
+			 change->data.tp.clear_toast_afterwards)
+		toptxn->txn_flags &= ~RBTXN_HAS_PARTIAL_CHANGE;
+
+	/*
+	 * Indicate a partial change for speculative inserts.  The change will be
+	 * considered as complete once we get the speculative confirm or abort
+	 * token.
+	 */
+	if (IsSpecInsert(change->action))
+		toptxn->txn_flags |= RBTXN_HAS_PARTIAL_CHANGE;
+	else if (rbtxn_has_partial_change(toptxn) &&
+			 IsSpecConfirmOrAbort(change->action))
+		toptxn->txn_flags &= ~RBTXN_HAS_PARTIAL_CHANGE;
+
+	/*
+	 * Stream the transaction if it is serialized before and the changes are
+	 * now complete in the top-level transaction.
+	 *
+	 * The reason for doing the streaming of such a transaction as soon as we
+	 * get the complete change for it is that previously it would have reached
+	 * the memory threshold and wouldn't get streamed because of incomplete
+	 * changes.  Delaying such transactions would increase apply lag for them.
+	 */
+	if (ReorderBufferCanStartStreaming(rb) &&
+		!(rbtxn_has_partial_change(toptxn)) &&
+		rbtxn_is_serialized(txn))
+		ReorderBufferStreamTXN(rb, toptxn);
+}
+
+/*
+ * Queue a change into a transaction so it can be replayed upon commit or will be
+ * streamed when we reach logical_decoding_work_mem threshold.
+ */
+void
+ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
+						 ReorderBufferChange *change, bool toast_insert)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+	/*
+	 * While streaming the previous changes we have detected that the
+	 * transaction is aborted.  So there is no point in collecting further
+	 * changes for it.
+	 */
+	if (txn->concurrent_abort)
+	{
+		/*
+		 * We don't need to update memory accounting for this change as we
+		 * have not added it to the queue yet.
+		 */
+		ReorderBufferReturnChange(rb, change, false);
+		return;
+	}
+
+	change->lsn = lsn;
+	change->txn = txn;
+
+	Assert(InvalidXLogRecPtr != lsn);
+	dlist_push_tail(&txn->changes, &change->node);
+	txn->nentries++;
+	txn->nentries_mem++;
+
+	/* update memory accounting information */
+	ReorderBufferChangeMemoryUpdate(rb, change, true,
+									ReorderBufferChangeSize(change));
+
+	/* process partial change */
+	ReorderBufferProcessPartialChange(rb, txn, change, toast_insert);
+
+	/* check the memory limits and evict something if needed */
+	ReorderBufferCheckMemoryLimit(rb);
+}
+
+/*
+ * A transactional message is queued to be processed upon commit and a
+ * non-transactional message gets processed immediately.
+ */
+void
+ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid,
+						  Snapshot snapshot, XLogRecPtr lsn,
+						  bool transactional, const char *prefix,
+						  Size message_size, const char *message)
+{
+	if (transactional)
+	{
+		MemoryContext oldcontext;
+		ReorderBufferChange *change;
+
+		Assert(xid != InvalidTransactionId);
+
+		oldcontext = MemoryContextSwitchTo(rb->context);
+
+		change = ReorderBufferGetChange(rb);
+		change->action = REORDER_BUFFER_CHANGE_MESSAGE;
+		change->data.msg.prefix = pstrdup(prefix);
+		change->data.msg.message_size = message_size;
+		change->data.msg.message = palloc(message_size);
+		memcpy(change->data.msg.message, message, message_size);
+
+		ReorderBufferQueueChange(rb, xid, lsn, change, false);
+
+		MemoryContextSwitchTo(oldcontext);
+	}
+	else
+	{
+		ReorderBufferTXN *txn = NULL;
+		volatile Snapshot snapshot_now = snapshot;
+
+		if (xid != InvalidTransactionId)
+			txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+		/* setup snapshot to allow catalog access */
+		SetupHistoricSnapshot(snapshot_now, NULL);
+		PG_TRY();
+		{
+			rb->message(rb, txn, lsn, false, prefix, message_size, message);
+
+			TeardownHistoricSnapshot(false);
+		}
+		PG_CATCH();
+		{
+			TeardownHistoricSnapshot(true);
+			PG_RE_THROW();
+		}
+		PG_END_TRY();
+	}
+}
+
+/*
+ * AssertTXNLsnOrder
+ *		Verify LSN ordering of transaction lists in the reorderbuffer
+ *
+ * Other LSN-related invariants are checked too.
+ *
+ * No-op if assertions are not in use.
+ */
+static void
+AssertTXNLsnOrder(ReorderBuffer *rb)
+{
+#ifdef USE_ASSERT_CHECKING
+	dlist_iter	iter;
+	XLogRecPtr	prev_first_lsn = InvalidXLogRecPtr;
+	XLogRecPtr	prev_base_snap_lsn = InvalidXLogRecPtr;
+
+	dlist_foreach(iter, &rb->toplevel_by_lsn)
+	{
+		ReorderBufferTXN *cur_txn = dlist_container(ReorderBufferTXN, node,
+													iter.cur);
+
+		/* start LSN must be set */
+		Assert(cur_txn->first_lsn != InvalidXLogRecPtr);
+
+		/* If there is an end LSN, it must be higher than start LSN */
+		if (cur_txn->end_lsn != InvalidXLogRecPtr)
+			Assert(cur_txn->first_lsn <= cur_txn->end_lsn);
+
+		/* Current initial LSN must be strictly higher than previous */
+		if (prev_first_lsn != InvalidXLogRecPtr)
+			Assert(prev_first_lsn < cur_txn->first_lsn);
+
+		/* known-as-subtxn txns must not be listed */
+		Assert(!rbtxn_is_known_subxact(cur_txn));
+
+		prev_first_lsn = cur_txn->first_lsn;
+	}
+
+	dlist_foreach(iter, &rb->txns_by_base_snapshot_lsn)
+	{
+		ReorderBufferTXN *cur_txn = dlist_container(ReorderBufferTXN,
+													base_snapshot_node,
+													iter.cur);
+
+		/* base snapshot (and its LSN) must be set */
+		Assert(cur_txn->base_snapshot != NULL);
+		Assert(cur_txn->base_snapshot_lsn != InvalidXLogRecPtr);
+
+		/* current LSN must be strictly higher than previous */
+		if (prev_base_snap_lsn != InvalidXLogRecPtr)
+			Assert(prev_base_snap_lsn < cur_txn->base_snapshot_lsn);
+
+		/* known-as-subtxn txns must not be listed */
+		Assert(!rbtxn_is_known_subxact(cur_txn));
+
+		prev_base_snap_lsn = cur_txn->base_snapshot_lsn;
+	}
+#endif
+}
+
+/*
+ * AssertChangeLsnOrder
+ *
+ * Check ordering of changes in the (sub)transaction.
+ */
+static void
+AssertChangeLsnOrder(ReorderBufferTXN *txn)
+{
+#ifdef USE_ASSERT_CHECKING
+	dlist_iter	iter;
+	XLogRecPtr	prev_lsn = txn->first_lsn;
+
+	dlist_foreach(iter, &txn->changes)
+	{
+		ReorderBufferChange *cur_change;
+
+		cur_change = dlist_container(ReorderBufferChange, node, iter.cur);
+
+		Assert(txn->first_lsn != InvalidXLogRecPtr);
+		Assert(cur_change->lsn != InvalidXLogRecPtr);
+		Assert(txn->first_lsn <= cur_change->lsn);
+
+		if (txn->end_lsn != InvalidXLogRecPtr)
+			Assert(cur_change->lsn <= txn->end_lsn);
+
+		Assert(prev_lsn <= cur_change->lsn);
+
+		prev_lsn = cur_change->lsn;
+	}
+#endif
+}
+
+/*
+ * ReorderBufferGetOldestTXN
+ *		Return oldest transaction in reorderbuffer
+ */
+ReorderBufferTXN *
+ReorderBufferGetOldestTXN(ReorderBuffer *rb)
+{
+	ReorderBufferTXN *txn;
+
+	AssertTXNLsnOrder(rb);
+
+	if (dlist_is_empty(&rb->toplevel_by_lsn))
+		return NULL;
+
+	txn = dlist_head_element(ReorderBufferTXN, node, &rb->toplevel_by_lsn);
+
+	Assert(!rbtxn_is_known_subxact(txn));
+	Assert(txn->first_lsn != InvalidXLogRecPtr);
+	return txn;
+}
+
+/*
+ * ReorderBufferGetOldestXmin
+ *		Return oldest Xmin in reorderbuffer
+ *
+ * Returns oldest possibly running Xid from the point of view of snapshots
+ * used in the transactions kept by reorderbuffer, or InvalidTransactionId if
+ * there are none.
+ *
+ * Since snapshots are assigned monotonically, this equals the Xmin of the
+ * base snapshot with minimal base_snapshot_lsn.
+ */
+TransactionId
+ReorderBufferGetOldestXmin(ReorderBuffer *rb)
+{
+	ReorderBufferTXN *txn;
+
+	AssertTXNLsnOrder(rb);
+
+	if (dlist_is_empty(&rb->txns_by_base_snapshot_lsn))
+		return InvalidTransactionId;
+
+	txn = dlist_head_element(ReorderBufferTXN, base_snapshot_node,
+							 &rb->txns_by_base_snapshot_lsn);
+	return txn->base_snapshot->xmin;
+}
+
+void
+ReorderBufferSetRestartPoint(ReorderBuffer *rb, XLogRecPtr ptr)
+{
+	rb->current_restart_decoding_lsn = ptr;
+}
+
+/*
+ * ReorderBufferAssignChild
+ *
+ * Make note that we know that subxid is a subtransaction of xid, seen as of
+ * the given lsn.
+ */
+void
+ReorderBufferAssignChild(ReorderBuffer *rb, TransactionId xid,
+						 TransactionId subxid, XLogRecPtr lsn)
+{
+	ReorderBufferTXN *txn;
+	ReorderBufferTXN *subtxn;
+	bool		new_top;
+	bool		new_sub;
+
+	txn = ReorderBufferTXNByXid(rb, xid, true, &new_top, lsn, true);
+	subtxn = ReorderBufferTXNByXid(rb, subxid, true, &new_sub, lsn, false);
+
+	if (!new_sub)
+	{
+		if (rbtxn_is_known_subxact(subtxn))
+		{
+			/* already associated, nothing to do */
+			return;
+		}
+		else
+		{
+			/*
+			 * We already saw this transaction, but initially added it to the
+			 * list of top-level txns.  Now that we know it's not top-level,
+			 * remove it from there.
+			 */
+			dlist_delete(&subtxn->node);
+		}
+	}
+
+	subtxn->txn_flags |= RBTXN_IS_SUBXACT;
+	subtxn->toplevel_xid = xid;
+	Assert(subtxn->nsubtxns == 0);
+
+	/* set the reference to top-level transaction */
+	subtxn->toptxn = txn;
+
+	/* add to subtransaction list */
+	dlist_push_tail(&txn->subtxns, &subtxn->node);
+	txn->nsubtxns++;
+
+	/* Possibly transfer the subtxn's snapshot to its top-level txn. */
+	ReorderBufferTransferSnapToParent(txn, subtxn);
+
+	/* Verify LSN-ordering invariant */
+	AssertTXNLsnOrder(rb);
+}
+
+/*
+ * ReorderBufferTransferSnapToParent
+ *		Transfer base snapshot from subtxn to top-level txn, if needed
+ *
+ * This is done if the top-level txn doesn't have a base snapshot, or if the
+ * subtxn's base snapshot has an earlier LSN than the top-level txn's base
+ * snapshot's LSN.  This can happen if there are no changes in the toplevel
+ * txn but there are some in the subtxn, or the first change in subtxn has
+ * earlier LSN than first change in the top-level txn and we learned about
+ * their kinship only now.
+ *
+ * The subtransaction's snapshot is cleared regardless of the transfer
+ * happening, since it's not needed anymore in either case.
+ *
+ * We do this as soon as we become aware of their kinship, to avoid queueing
+ * extra snapshots to txns known-as-subtxns -- only top-level txns will
+ * receive further snapshots.
+ */
+static void
+ReorderBufferTransferSnapToParent(ReorderBufferTXN *txn,
+								  ReorderBufferTXN *subtxn)
+{
+	Assert(subtxn->toplevel_xid == txn->xid);
+
+	if (subtxn->base_snapshot != NULL)
+	{
+		if (txn->base_snapshot == NULL ||
+			subtxn->base_snapshot_lsn < txn->base_snapshot_lsn)
+		{
+			/*
+			 * If the toplevel transaction already has a base snapshot but
+			 * it's newer than the subxact's, purge it.
+			 */
+			if (txn->base_snapshot != NULL)
+			{
+				SnapBuildSnapDecRefcount(txn->base_snapshot);
+				dlist_delete(&txn->base_snapshot_node);
+			}
+
+			/*
+			 * The snapshot is now the top transaction's; transfer it, and
+			 * adjust the list position of the top transaction in the list by
+			 * moving it to where the subtransaction is.
+			 */
+			txn->base_snapshot = subtxn->base_snapshot;
+			txn->base_snapshot_lsn = subtxn->base_snapshot_lsn;
+			dlist_insert_before(&subtxn->base_snapshot_node,
+								&txn->base_snapshot_node);
+
+			/*
+			 * The subtransaction doesn't have a snapshot anymore (so it
+			 * mustn't be in the list.)
+			 */
+			subtxn->base_snapshot = NULL;
+			subtxn->base_snapshot_lsn = InvalidXLogRecPtr;
+			dlist_delete(&subtxn->base_snapshot_node);
+		}
+		else
+		{
+			/* Base snap of toplevel is fine, so subxact's is not needed */
+			SnapBuildSnapDecRefcount(subtxn->base_snapshot);
+			dlist_delete(&subtxn->base_snapshot_node);
+			subtxn->base_snapshot = NULL;
+			subtxn->base_snapshot_lsn = InvalidXLogRecPtr;
+		}
+	}
+}
+
+/*
+ * Associate a subtransaction with its toplevel transaction at commit
+ * time. There may be no further changes added after this.
+ */
+void
+ReorderBufferCommitChild(ReorderBuffer *rb, TransactionId xid,
+						 TransactionId subxid, XLogRecPtr commit_lsn,
+						 XLogRecPtr end_lsn)
+{
+	ReorderBufferTXN *subtxn;
+
+	subtxn = ReorderBufferTXNByXid(rb, subxid, false, NULL,
+								   InvalidXLogRecPtr, false);
+
+	/*
+	 * No need to do anything if that subtxn didn't contain any changes
+	 */
+	if (!subtxn)
+		return;
+
+	subtxn->final_lsn = commit_lsn;
+	subtxn->end_lsn = end_lsn;
+
+	/*
+	 * Assign this subxact as a child of the toplevel xact (no-op if already
+	 * done.)
+	 */
+	ReorderBufferAssignChild(rb, xid, subxid, InvalidXLogRecPtr);
+}
+
+
+/*
+ * Support for efficiently iterating over a transaction's and its
+ * subtransactions' changes.
+ *
+ * We do by doing a k-way merge between transactions/subtransactions. For that
+ * we model the current heads of the different transactions as a binary heap
+ * so we easily know which (sub-)transaction has the change with the smallest
+ * lsn next.
+ *
+ * We assume the changes in individual transactions are already sorted by LSN.
+ */
+
+/*
+ * Binary heap comparison function.
+ */
+static int
+ReorderBufferIterCompare(Datum a, Datum b, void *arg)
+{
+	ReorderBufferIterTXNState *state = (ReorderBufferIterTXNState *) arg;
+	XLogRecPtr	pos_a = state->entries[DatumGetInt32(a)].lsn;
+	XLogRecPtr	pos_b = state->entries[DatumGetInt32(b)].lsn;
+
+	if (pos_a < pos_b)
+		return 1;
+	else if (pos_a == pos_b)
+		return 0;
+	return -1;
+}
+
+/*
+ * Allocate & initialize an iterator which iterates in lsn order over a
+ * transaction and all its subtransactions.
+ *
+ * Note: The iterator state is returned through iter_state parameter rather
+ * than the function's return value.  This is because the state gets cleaned up
+ * in a PG_CATCH block in the caller, so we want to make sure the caller gets
+ * back the state even if this function throws an exception.
+ */
+static void
+ReorderBufferIterTXNInit(ReorderBuffer *rb, ReorderBufferTXN *txn,
+						 ReorderBufferIterTXNState *volatile *iter_state)
+{
+	Size		nr_txns = 0;
+	ReorderBufferIterTXNState *state;
+	dlist_iter	cur_txn_i;
+	int32		off;
+
+	*iter_state = NULL;
+
+	/* Check ordering of changes in the toplevel transaction. */
+	AssertChangeLsnOrder(txn);
+
+	/*
+	 * Calculate the size of our heap: one element for every transaction that
+	 * contains changes.  (Besides the transactions already in the reorder
+	 * buffer, we count the one we were directly passed.)
+	 */
+	if (txn->nentries > 0)
+		nr_txns++;
+
+	dlist_foreach(cur_txn_i, &txn->subtxns)
+	{
+		ReorderBufferTXN *cur_txn;
+
+		cur_txn = dlist_container(ReorderBufferTXN, node, cur_txn_i.cur);
+
+		/* Check ordering of changes in this subtransaction. */
+		AssertChangeLsnOrder(cur_txn);
+
+		if (cur_txn->nentries > 0)
+			nr_txns++;
+	}
+
+	/* allocate iteration state */
+	state = (ReorderBufferIterTXNState *)
+		MemoryContextAllocZero(rb->context,
+							   sizeof(ReorderBufferIterTXNState) +
+							   sizeof(ReorderBufferIterTXNEntry) * nr_txns);
+
+	state->nr_txns = nr_txns;
+	dlist_init(&state->old_change);
+
+	for (off = 0; off < state->nr_txns; off++)
+	{
+		state->entries[off].file.vfd = -1;
+		state->entries[off].segno = 0;
+	}
+
+	/* allocate heap */
+	state->heap = binaryheap_allocate(state->nr_txns,
+									  ReorderBufferIterCompare,
+									  state);
+
+	/* Now that the state fields are initialized, it is safe to return it. */
+	*iter_state = state;
+
+	/*
+	 * Now insert items into the binary heap, in an unordered fashion.  (We
+	 * will run a heap assembly step at the end; this is more efficient.)
+	 */
+
+	off = 0;
+
+	/* add toplevel transaction if it contains changes */
+	if (txn->nentries > 0)
+	{
+		ReorderBufferChange *cur_change;
+
+		if (rbtxn_is_serialized(txn))
+		{
+			/* serialize remaining changes */
+			ReorderBufferSerializeTXN(rb, txn);
+			ReorderBufferRestoreChanges(rb, txn, &state->entries[off].file,
+										&state->entries[off].segno);
+		}
+
+		cur_change = dlist_head_element(ReorderBufferChange, node,
+										&txn->changes);
+
+		state->entries[off].lsn = cur_change->lsn;
+		state->entries[off].change = cur_change;
+		state->entries[off].txn = txn;
+
+		binaryheap_add_unordered(state->heap, Int32GetDatum(off++));
+	}
+
+	/* add subtransactions if they contain changes */
+	dlist_foreach(cur_txn_i, &txn->subtxns)
+	{
+		ReorderBufferTXN *cur_txn;
+
+		cur_txn = dlist_container(ReorderBufferTXN, node, cur_txn_i.cur);
+
+		if (cur_txn->nentries > 0)
+		{
+			ReorderBufferChange *cur_change;
+
+			if (rbtxn_is_serialized(cur_txn))
+			{
+				/* serialize remaining changes */
+				ReorderBufferSerializeTXN(rb, cur_txn);
+				ReorderBufferRestoreChanges(rb, cur_txn,
+											&state->entries[off].file,
+											&state->entries[off].segno);
+			}
+			cur_change = dlist_head_element(ReorderBufferChange, node,
+											&cur_txn->changes);
+
+			state->entries[off].lsn = cur_change->lsn;
+			state->entries[off].change = cur_change;
+			state->entries[off].txn = cur_txn;
+
+			binaryheap_add_unordered(state->heap, Int32GetDatum(off++));
+		}
+	}
+
+	/* assemble a valid binary heap */
+	binaryheap_build(state->heap);
+}
+
+/*
+ * Return the next change when iterating over a transaction and its
+ * subtransactions.
+ *
+ * Returns NULL when no further changes exist.
+ */
+static ReorderBufferChange *
+ReorderBufferIterTXNNext(ReorderBuffer *rb, ReorderBufferIterTXNState *state)
+{
+	ReorderBufferChange *change;
+	ReorderBufferIterTXNEntry *entry;
+	int32		off;
+
+	/* nothing there anymore */
+	if (state->heap->bh_size == 0)
+		return NULL;
+
+	off = DatumGetInt32(binaryheap_first(state->heap));
+	entry = &state->entries[off];
+
+	/* free memory we might have "leaked" in the previous *Next call */
+	if (!dlist_is_empty(&state->old_change))
+	{
+		change = dlist_container(ReorderBufferChange, node,
+								 dlist_pop_head_node(&state->old_change));
+		ReorderBufferReturnChange(rb, change, true);
+		Assert(dlist_is_empty(&state->old_change));
+	}
+
+	change = entry->change;
+
+	/*
+	 * update heap with information about which transaction has the next
+	 * relevant change in LSN order
+	 */
+
+	/* there are in-memory changes */
+	if (dlist_has_next(&entry->txn->changes, &entry->change->node))
+	{
+		dlist_node *next = dlist_next_node(&entry->txn->changes, &change->node);
+		ReorderBufferChange *next_change =
+		dlist_container(ReorderBufferChange, node, next);
+
+		/* txn stays the same */
+		state->entries[off].lsn = next_change->lsn;
+		state->entries[off].change = next_change;
+
+		binaryheap_replace_first(state->heap, Int32GetDatum(off));
+		return change;
+	}
+
+	/* try to load changes from disk */
+	if (entry->txn->nentries != entry->txn->nentries_mem)
+	{
+		/*
+		 * Ugly: restoring changes will reuse *Change records, thus delete the
+		 * current one from the per-tx list and only free in the next call.
+		 */
+		dlist_delete(&change->node);
+		dlist_push_tail(&state->old_change, &change->node);
+
+		/*
+		 * Update the total bytes processed by the txn for which we are
+		 * releasing the current set of changes and restoring the new set of
+		 * changes.
+		 */
+		rb->totalBytes += entry->txn->size;
+		if (ReorderBufferRestoreChanges(rb, entry->txn, &entry->file,
+										&state->entries[off].segno))
+		{
+			/* successfully restored changes from disk */
+			ReorderBufferChange *next_change =
+			dlist_head_element(ReorderBufferChange, node,
+							   &entry->txn->changes);
+
+			elog(DEBUG2, "restored %u/%u changes from disk",
+				 (uint32) entry->txn->nentries_mem,
+				 (uint32) entry->txn->nentries);
+
+			Assert(entry->txn->nentries_mem);
+			/* txn stays the same */
+			state->entries[off].lsn = next_change->lsn;
+			state->entries[off].change = next_change;
+			binaryheap_replace_first(state->heap, Int32GetDatum(off));
+
+			return change;
+		}
+	}
+
+	/* ok, no changes there anymore, remove */
+	binaryheap_remove_first(state->heap);
+
+	return change;
+}
+
+/*
+ * Deallocate the iterator
+ */
+static void
+ReorderBufferIterTXNFinish(ReorderBuffer *rb,
+						   ReorderBufferIterTXNState *state)
+{
+	int32		off;
+
+	for (off = 0; off < state->nr_txns; off++)
+	{
+		if (state->entries[off].file.vfd != -1)
+			FileClose(state->entries[off].file.vfd);
+	}
+
+	/* free memory we might have "leaked" in the last *Next call */
+	if (!dlist_is_empty(&state->old_change))
+	{
+		ReorderBufferChange *change;
+
+		change = dlist_container(ReorderBufferChange, node,
+								 dlist_pop_head_node(&state->old_change));
+		ReorderBufferReturnChange(rb, change, true);
+		Assert(dlist_is_empty(&state->old_change));
+	}
+
+	binaryheap_free(state->heap);
+	pfree(state);
+}
+
+/*
+ * Cleanup the contents of a transaction, usually after the transaction
+ * committed or aborted.
+ */
+static void
+ReorderBufferCleanupTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	bool		found;
+	dlist_mutable_iter iter;
+
+	/* cleanup subtransactions & their changes */
+	dlist_foreach_modify(iter, &txn->subtxns)
+	{
+		ReorderBufferTXN *subtxn;
+
+		subtxn = dlist_container(ReorderBufferTXN, node, iter.cur);
+
+		/*
+		 * Subtransactions are always associated to the toplevel TXN, even if
+		 * they originally were happening inside another subtxn, so we won't
+		 * ever recurse more than one level deep here.
+		 */
+		Assert(rbtxn_is_known_subxact(subtxn));
+		Assert(subtxn->nsubtxns == 0);
+
+		ReorderBufferCleanupTXN(rb, subtxn);
+	}
+
+	/* cleanup changes in the txn */
+	dlist_foreach_modify(iter, &txn->changes)
+	{
+		ReorderBufferChange *change;
+
+		change = dlist_container(ReorderBufferChange, node, iter.cur);
+
+		/* Check we're not mixing changes from different transactions. */
+		Assert(change->txn == txn);
+
+		ReorderBufferReturnChange(rb, change, true);
+	}
+
+	/*
+	 * Cleanup the tuplecids we stored for decoding catalog snapshot access.
+	 * They are always stored in the toplevel transaction.
+	 */
+	dlist_foreach_modify(iter, &txn->tuplecids)
+	{
+		ReorderBufferChange *change;
+
+		change = dlist_container(ReorderBufferChange, node, iter.cur);
+
+		/* Check we're not mixing changes from different transactions. */
+		Assert(change->txn == txn);
+		Assert(change->action == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID);
+
+		ReorderBufferReturnChange(rb, change, true);
+	}
+
+	/*
+	 * Cleanup the base snapshot, if set.
+	 */
+	if (txn->base_snapshot != NULL)
+	{
+		SnapBuildSnapDecRefcount(txn->base_snapshot);
+		dlist_delete(&txn->base_snapshot_node);
+	}
+
+	/*
+	 * Cleanup the snapshot for the last streamed run.
+	 */
+	if (txn->snapshot_now != NULL)
+	{
+		Assert(rbtxn_is_streamed(txn));
+		ReorderBufferFreeSnap(rb, txn->snapshot_now);
+	}
+
+	/*
+	 * Remove TXN from its containing list.
+	 *
+	 * Note: if txn is known as subxact, we are deleting the TXN from its
+	 * parent's list of known subxacts; this leaves the parent's nsubxacts
+	 * count too high, but we don't care.  Otherwise, we are deleting the TXN
+	 * from the LSN-ordered list of toplevel TXNs.
+	 */
+	dlist_delete(&txn->node);
+
+	/* now remove reference from buffer */
+	hash_search(rb->by_txn,
+				(void *) &txn->xid,
+				HASH_REMOVE,
+				&found);
+	Assert(found);
+
+	/* remove entries spilled to disk */
+	if (rbtxn_is_serialized(txn))
+		ReorderBufferRestoreCleanup(rb, txn);
+
+	/* deallocate */
+	ReorderBufferReturnTXN(rb, txn);
+}
+
+/*
+ * Discard changes from a transaction (and subtransactions), either after
+ * streaming or decoding them at PREPARE. Keep the remaining info -
+ * transactions, tuplecids, invalidations and snapshots.
+ *
+ * We additionaly remove tuplecids after decoding the transaction at prepare
+ * time as we only need to perform invalidation at rollback or commit prepared.
+ *
+ * 'txn_prepared' indicates that we have decoded the transaction at prepare
+ * time.
+ */
+static void
+ReorderBufferTruncateTXN(ReorderBuffer *rb, ReorderBufferTXN *txn, bool txn_prepared)
+{
+	dlist_mutable_iter iter;
+
+	/* cleanup subtransactions & their changes */
+	dlist_foreach_modify(iter, &txn->subtxns)
+	{
+		ReorderBufferTXN *subtxn;
+
+		subtxn = dlist_container(ReorderBufferTXN, node, iter.cur);
+
+		/*
+		 * Subtransactions are always associated to the toplevel TXN, even if
+		 * they originally were happening inside another subtxn, so we won't
+		 * ever recurse more than one level deep here.
+		 */
+		Assert(rbtxn_is_known_subxact(subtxn));
+		Assert(subtxn->nsubtxns == 0);
+
+		ReorderBufferTruncateTXN(rb, subtxn, txn_prepared);
+	}
+
+	/* cleanup changes in the txn */
+	dlist_foreach_modify(iter, &txn->changes)
+	{
+		ReorderBufferChange *change;
+
+		change = dlist_container(ReorderBufferChange, node, iter.cur);
+
+		/* Check we're not mixing changes from different transactions. */
+		Assert(change->txn == txn);
+
+		/* remove the change from it's containing list */
+		dlist_delete(&change->node);
+
+		ReorderBufferReturnChange(rb, change, true);
+	}
+
+	/*
+	 * Mark the transaction as streamed.
+	 *
+	 * The toplevel transaction, identified by (toptxn==NULL), is marked as
+	 * streamed always, even if it does not contain any changes (that is, when
+	 * all the changes are in subtransactions).
+	 *
+	 * For subtransactions, we only mark them as streamed when there are
+	 * changes in them.
+	 *
+	 * We do it this way because of aborts - we don't want to send aborts for
+	 * XIDs the downstream is not aware of. And of course, it always knows
+	 * about the toplevel xact (we send the XID in all messages), but we never
+	 * stream XIDs of empty subxacts.
+	 */
+	if ((!txn_prepared) && ((!txn->toptxn) || (txn->nentries_mem != 0)))
+		txn->txn_flags |= RBTXN_IS_STREAMED;
+
+	if (txn_prepared)
+	{
+		/*
+		 * If this is a prepared txn, cleanup the tuplecids we stored for
+		 * decoding catalog snapshot access. They are always stored in the
+		 * toplevel transaction.
+		 */
+		dlist_foreach_modify(iter, &txn->tuplecids)
+		{
+			ReorderBufferChange *change;
+
+			change = dlist_container(ReorderBufferChange, node, iter.cur);
+
+			/* Check we're not mixing changes from different transactions. */
+			Assert(change->txn == txn);
+			Assert(change->action == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID);
+
+			/* Remove the change from its containing list. */
+			dlist_delete(&change->node);
+
+			ReorderBufferReturnChange(rb, change, true);
+		}
+	}
+
+	/*
+	 * Destroy the (relfilenode, ctid) hashtable, so that we don't leak any
+	 * memory. We could also keep the hash table and update it with new ctid
+	 * values, but this seems simpler and good enough for now.
+	 */
+	if (txn->tuplecid_hash != NULL)
+	{
+		hash_destroy(txn->tuplecid_hash);
+		txn->tuplecid_hash = NULL;
+	}
+
+	/* If this txn is serialized then clean the disk space. */
+	if (rbtxn_is_serialized(txn))
+	{
+		ReorderBufferRestoreCleanup(rb, txn);
+		txn->txn_flags &= ~RBTXN_IS_SERIALIZED;
+
+		/*
+		 * We set this flag to indicate if the transaction is ever serialized.
+		 * We need this to accurately update the stats as otherwise the same
+		 * transaction can be counted as serialized multiple times.
+		 */
+		txn->txn_flags |= RBTXN_IS_SERIALIZED_CLEAR;
+	}
+
+	/* also reset the number of entries in the transaction */
+	txn->nentries_mem = 0;
+	txn->nentries = 0;
+}
+
+/*
+ * Build a hash with a (relfilenode, ctid) -> (cmin, cmax) mapping for use by
+ * HeapTupleSatisfiesHistoricMVCC.
+ */
+static void
+ReorderBufferBuildTupleCidHash(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	dlist_iter	iter;
+	HASHCTL		hash_ctl;
+
+	if (!rbtxn_has_catalog_changes(txn) || dlist_is_empty(&txn->tuplecids))
+		return;
+
+	hash_ctl.keysize = sizeof(ReorderBufferTupleCidKey);
+	hash_ctl.entrysize = sizeof(ReorderBufferTupleCidEnt);
+	hash_ctl.hcxt = rb->context;
+
+	/*
+	 * create the hash with the exact number of to-be-stored tuplecids from
+	 * the start
+	 */
+	txn->tuplecid_hash =
+		hash_create("ReorderBufferTupleCid", txn->ntuplecids, &hash_ctl,
+					HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
+	dlist_foreach(iter, &txn->tuplecids)
+	{
+		ReorderBufferTupleCidKey key;
+		ReorderBufferTupleCidEnt *ent;
+		bool		found;
+		ReorderBufferChange *change;
+
+		change = dlist_container(ReorderBufferChange, node, iter.cur);
+
+		Assert(change->action == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID);
+
+		/* be careful about padding */
+		memset(&key, 0, sizeof(ReorderBufferTupleCidKey));
+
+		key.relnode = change->data.tuplecid.node;
+
+		ItemPointerCopy(&change->data.tuplecid.tid,
+						&key.tid);
+
+		ent = (ReorderBufferTupleCidEnt *)
+			hash_search(txn->tuplecid_hash,
+						(void *) &key,
+						HASH_ENTER,
+						&found);
+		if (!found)
+		{
+			ent->cmin = change->data.tuplecid.cmin;
+			ent->cmax = change->data.tuplecid.cmax;
+			ent->combocid = change->data.tuplecid.combocid;
+		}
+		else
+		{
+			/*
+			 * Maybe we already saw this tuple before in this transaction, but
+			 * if so it must have the same cmin.
+			 */
+			Assert(ent->cmin == change->data.tuplecid.cmin);
+
+			/*
+			 * cmax may be initially invalid, but once set it can only grow,
+			 * and never become invalid again.
+			 */
+			Assert((ent->cmax == InvalidCommandId) ||
+				   ((change->data.tuplecid.cmax != InvalidCommandId) &&
+					(change->data.tuplecid.cmax > ent->cmax)));
+			ent->cmax = change->data.tuplecid.cmax;
+		}
+	}
+}
+
+/*
+ * Copy a provided snapshot so we can modify it privately. This is needed so
+ * that catalog modifying transactions can look into intermediate catalog
+ * states.
+ */
+static Snapshot
+ReorderBufferCopySnap(ReorderBuffer *rb, Snapshot orig_snap,
+					  ReorderBufferTXN *txn, CommandId cid)
+{
+	Snapshot	snap;
+	dlist_iter	iter;
+	int			i = 0;
+	Size		size;
+
+	size = sizeof(SnapshotData) +
+		sizeof(TransactionId) * orig_snap->xcnt +
+		sizeof(TransactionId) * (txn->nsubtxns + 1);
+
+	snap = MemoryContextAllocZero(rb->context, size);
+	memcpy(snap, orig_snap, sizeof(SnapshotData));
+
+	snap->copied = true;
+	snap->active_count = 1;		/* mark as active so nobody frees it */
+	snap->regd_count = 0;
+	snap->xip = (TransactionId *) (snap + 1);
+
+	memcpy(snap->xip, orig_snap->xip, sizeof(TransactionId) * snap->xcnt);
+
+	/*
+	 * snap->subxip contains all txids that belong to our transaction which we
+	 * need to check via cmin/cmax. That's why we store the toplevel
+	 * transaction in there as well.
+	 */
+	snap->subxip = snap->xip + snap->xcnt;
+	snap->subxip[i++] = txn->xid;
+
+	/*
+	 * subxcnt isn't decreased when subtransactions abort, so count manually.
+	 * Since it's an upper boundary it is safe to use it for the allocation
+	 * above.
+	 */
+	snap->subxcnt = 1;
+
+	dlist_foreach(iter, &txn->subtxns)
+	{
+		ReorderBufferTXN *sub_txn;
+
+		sub_txn = dlist_container(ReorderBufferTXN, node, iter.cur);
+		snap->subxip[i++] = sub_txn->xid;
+		snap->subxcnt++;
+	}
+
+	/* sort so we can bsearch() later */
+	qsort(snap->subxip, snap->subxcnt, sizeof(TransactionId), xidComparator);
+
+	/* store the specified current CommandId */
+	snap->curcid = cid;
+
+	return snap;
+}
+
+/*
+ * Free a previously ReorderBufferCopySnap'ed snapshot
+ */
+static void
+ReorderBufferFreeSnap(ReorderBuffer *rb, Snapshot snap)
+{
+	if (snap->copied)
+		pfree(snap);
+	else
+		SnapBuildSnapDecRefcount(snap);
+}
+
+/*
+ * If the transaction was (partially) streamed, we need to prepare or commit
+ * it in a 'streamed' way.  That is, we first stream the remaining part of the
+ * transaction, and then invoke stream_prepare or stream_commit message as per
+ * the case.
+ */
+static void
+ReorderBufferStreamCommit(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	/* we should only call this for previously streamed transactions */
+	Assert(rbtxn_is_streamed(txn));
+
+	ReorderBufferStreamTXN(rb, txn);
+
+	if (rbtxn_prepared(txn))
+	{
+		/*
+		 * Note, we send stream prepare even if a concurrent abort is
+		 * detected. See DecodePrepare for more information.
+		 */
+		rb->stream_prepare(rb, txn, txn->final_lsn);
+
+		/*
+		 * This is a PREPARED transaction, part of a two-phase commit. The
+		 * full cleanup will happen as part of the COMMIT PREPAREDs, so now
+		 * just truncate txn by removing changes and tuple_cids.
+		 */
+		ReorderBufferTruncateTXN(rb, txn, true);
+		/* Reset the CheckXidAlive */
+		CheckXidAlive = InvalidTransactionId;
+	}
+	else
+	{
+		rb->stream_commit(rb, txn, txn->final_lsn);
+		ReorderBufferCleanupTXN(rb, txn);
+	}
+}
+
+/*
+ * Set xid to detect concurrent aborts.
+ *
+ * While streaming an in-progress transaction or decoding a prepared
+ * transaction there is a possibility that the (sub)transaction might get
+ * aborted concurrently.  In such case if the (sub)transaction has catalog
+ * update then we might decode the tuple using wrong catalog version.  For
+ * example, suppose there is one catalog tuple with (xmin: 500, xmax: 0).  Now,
+ * the transaction 501 updates the catalog tuple and after that we will have
+ * two tuples (xmin: 500, xmax: 501) and (xmin: 501, xmax: 0).  Now, if 501 is
+ * aborted and some other transaction say 502 updates the same catalog tuple
+ * then the first tuple will be changed to (xmin: 500, xmax: 502).  So, the
+ * problem is that when we try to decode the tuple inserted/updated in 501
+ * after the catalog update, we will see the catalog tuple with (xmin: 500,
+ * xmax: 502) as visible because it will consider that the tuple is deleted by
+ * xid 502 which is not visible to our snapshot.  And when we will try to
+ * decode with that catalog tuple, it can lead to a wrong result or a crash.
+ * So, it is necessary to detect concurrent aborts to allow streaming of
+ * in-progress transactions or decoding of prepared  transactions.
+ *
+ * For detecting the concurrent abort we set CheckXidAlive to the current
+ * (sub)transaction's xid for which this change belongs to.  And, during
+ * catalog scan we can check the status of the xid and if it is aborted we will
+ * report a specific error so that we can stop streaming current transaction
+ * and discard the already streamed changes on such an error.  We might have
+ * already streamed some of the changes for the aborted (sub)transaction, but
+ * that is fine because when we decode the abort we will stream abort message
+ * to truncate the changes in the subscriber. Similarly, for prepared
+ * transactions, we stop decoding if concurrent abort is detected and then
+ * rollback the changes when rollback prepared is encountered. See
+ * DecodePrepare.
+ */
+static inline void
+SetupCheckXidLive(TransactionId xid)
+{
+	/*
+	 * If the input transaction id is already set as a CheckXidAlive then
+	 * nothing to do.
+	 */
+	if (TransactionIdEquals(CheckXidAlive, xid))
+		return;
+
+	/*
+	 * setup CheckXidAlive if it's not committed yet.  We don't check if the
+	 * xid is aborted.  That will happen during catalog access.
+	 */
+	if (!TransactionIdDidCommit(xid))
+		CheckXidAlive = xid;
+	else
+		CheckXidAlive = InvalidTransactionId;
+}
+
+/*
+ * Helper function for ReorderBufferProcessTXN for applying change.
+ */
+static inline void
+ReorderBufferApplyChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
+						 Relation relation, ReorderBufferChange *change,
+						 bool streaming)
+{
+	if (streaming)
+		rb->stream_change(rb, txn, relation, change);
+	else
+		rb->apply_change(rb, txn, relation, change);
+}
+
+/*
+ * Helper function for ReorderBufferProcessTXN for applying the truncate.
+ */
+static inline void
+ReorderBufferApplyTruncate(ReorderBuffer *rb, ReorderBufferTXN *txn,
+						   int nrelations, Relation *relations,
+						   ReorderBufferChange *change, bool streaming)
+{
+	if (streaming)
+		rb->stream_truncate(rb, txn, nrelations, relations, change);
+	else
+		rb->apply_truncate(rb, txn, nrelations, relations, change);
+}
+
+/*
+ * Helper function for ReorderBufferProcessTXN for applying the message.
+ */
+static inline void
+ReorderBufferApplyMessage(ReorderBuffer *rb, ReorderBufferTXN *txn,
+						  ReorderBufferChange *change, bool streaming)
+{
+	if (streaming)
+		rb->stream_message(rb, txn, change->lsn, true,
+						   change->data.msg.prefix,
+						   change->data.msg.message_size,
+						   change->data.msg.message);
+	else
+		rb->message(rb, txn, change->lsn, true,
+					change->data.msg.prefix,
+					change->data.msg.message_size,
+					change->data.msg.message);
+}
+
+/*
+ * Function to store the command id and snapshot at the end of the current
+ * stream so that we can reuse the same while sending the next stream.
+ */
+static inline void
+ReorderBufferSaveTXNSnapshot(ReorderBuffer *rb, ReorderBufferTXN *txn,
+							 Snapshot snapshot_now, CommandId command_id)
+{
+	txn->command_id = command_id;
+
+	/* Avoid copying if it's already copied. */
+	if (snapshot_now->copied)
+		txn->snapshot_now = snapshot_now;
+	else
+		txn->snapshot_now = ReorderBufferCopySnap(rb, snapshot_now,
+												  txn, command_id);
+}
+
+/*
+ * Helper function for ReorderBufferProcessTXN to handle the concurrent
+ * abort of the streaming transaction.  This resets the TXN such that it
+ * can be used to stream the remaining data of transaction being processed.
+ * This can happen when the subtransaction is aborted and we still want to
+ * continue processing the main or other subtransactions data.
+ */
+static void
+ReorderBufferResetTXN(ReorderBuffer *rb, ReorderBufferTXN *txn,
+					  Snapshot snapshot_now,
+					  CommandId command_id,
+					  XLogRecPtr last_lsn,
+					  ReorderBufferChange *specinsert)
+{
+	/* Discard the changes that we just streamed */
+	ReorderBufferTruncateTXN(rb, txn, rbtxn_prepared(txn));
+
+	/* Free all resources allocated for toast reconstruction */
+	ReorderBufferToastReset(rb, txn);
+
+	/* Return the spec insert change if it is not NULL */
+	if (specinsert != NULL)
+	{
+		ReorderBufferReturnChange(rb, specinsert, true);
+		specinsert = NULL;
+	}
+
+	/*
+	 * For the streaming case, stop the stream and remember the command ID and
+	 * snapshot for the streaming run.
+	 */
+	if (rbtxn_is_streamed(txn))
+	{
+		rb->stream_stop(rb, txn, last_lsn);
+		ReorderBufferSaveTXNSnapshot(rb, txn, snapshot_now, command_id);
+	}
+}
+
+/*
+ * Helper function for ReorderBufferReplay and ReorderBufferStreamTXN.
+ *
+ * Send data of a transaction (and its subtransactions) to the
+ * output plugin. We iterate over the top and subtransactions (using a k-way
+ * merge) and replay the changes in lsn order.
+ *
+ * If streaming is true then data will be sent using stream API.
+ *
+ * Note: "volatile" markers on some parameters are to avoid trouble with
+ * PG_TRY inside the function.
+ */
+static void
+ReorderBufferProcessTXN(ReorderBuffer *rb, ReorderBufferTXN *txn,
+						XLogRecPtr commit_lsn,
+						volatile Snapshot snapshot_now,
+						volatile CommandId command_id,
+						bool streaming)
+{
+	bool		using_subtxn;
+	MemoryContext ccxt = CurrentMemoryContext;
+	ReorderBufferIterTXNState *volatile iterstate = NULL;
+	volatile XLogRecPtr prev_lsn = InvalidXLogRecPtr;
+	ReorderBufferChange *volatile specinsert = NULL;
+	volatile bool stream_started = false;
+	ReorderBufferTXN *volatile curtxn = NULL;
+
+	/* build data to be able to lookup the CommandIds of catalog tuples */
+	ReorderBufferBuildTupleCidHash(rb, txn);
+
+	/* setup the initial snapshot */
+	SetupHistoricSnapshot(snapshot_now, txn->tuplecid_hash);
+
+	/*
+	 * Decoding needs access to syscaches et al., which in turn use
+	 * heavyweight locks and such. Thus we need to have enough state around to
+	 * keep track of those.  The easiest way is to simply use a transaction
+	 * internally.  That also allows us to easily enforce that nothing writes
+	 * to the database by checking for xid assignments.
+	 *
+	 * When we're called via the SQL SRF there's already a transaction
+	 * started, so start an explicit subtransaction there.
+	 */
+	using_subtxn = IsTransactionOrTransactionBlock();
+
+	PG_TRY();
+	{
+		ReorderBufferChange *change;
+
+		if (using_subtxn)
+			BeginInternalSubTransaction(streaming ? "stream" : "replay");
+		else
+			StartTransactionCommand();
+
+		/*
+		 * We only need to send begin/begin-prepare for non-streamed
+		 * transactions.
+		 */
+		if (!streaming)
+		{
+			if (rbtxn_prepared(txn))
+				rb->begin_prepare(rb, txn);
+			else
+				rb->begin(rb, txn);
+		}
+
+		ReorderBufferIterTXNInit(rb, txn, &iterstate);
+		while ((change = ReorderBufferIterTXNNext(rb, iterstate)) != NULL)
+		{
+			Relation	relation = NULL;
+			Oid			reloid;
+
+			/*
+			 * We can't call start stream callback before processing first
+			 * change.
+			 */
+			if (prev_lsn == InvalidXLogRecPtr)
+			{
+				if (streaming)
+				{
+					txn->origin_id = change->origin_id;
+					rb->stream_start(rb, txn, change->lsn);
+					stream_started = true;
+				}
+			}
+
+			/*
+			 * Enforce correct ordering of changes, merged from multiple
+			 * subtransactions. The changes may have the same LSN due to
+			 * MULTI_INSERT xlog records.
+			 */
+			Assert(prev_lsn == InvalidXLogRecPtr || prev_lsn <= change->lsn);
+
+			prev_lsn = change->lsn;
+
+			/*
+			 * Set the current xid to detect concurrent aborts. This is
+			 * required for the cases when we decode the changes before the
+			 * COMMIT record is processed.
+			 */
+			if (streaming || rbtxn_prepared(change->txn))
+			{
+				curtxn = change->txn;
+				SetupCheckXidLive(curtxn->xid);
+			}
+
+			switch (change->action)
+			{
+				case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
+
+					/*
+					 * Confirmation for speculative insertion arrived. Simply
+					 * use as a normal record. It'll be cleaned up at the end
+					 * of INSERT processing.
+					 */
+					if (specinsert == NULL)
+						elog(ERROR, "invalid ordering of speculative insertion changes");
+					Assert(specinsert->data.tp.oldtuple == NULL);
+					change = specinsert;
+					change->action = REORDER_BUFFER_CHANGE_INSERT;
+
+					/* intentionally fall through */
+				case REORDER_BUFFER_CHANGE_INSERT:
+				case REORDER_BUFFER_CHANGE_UPDATE:
+				case REORDER_BUFFER_CHANGE_DELETE:
+					Assert(snapshot_now);
+
+					reloid = RelidByRelfilenode(change->data.tp.relnode.spcNode,
+												change->data.tp.relnode.relNode);
+
+					/*
+					 * Mapped catalog tuple without data, emitted while
+					 * catalog table was in the process of being rewritten. We
+					 * can fail to look up the relfilenode, because the
+					 * relmapper has no "historic" view, in contrast to the
+					 * normal catalog during decoding. Thus repeated rewrites
+					 * can cause a lookup failure. That's OK because we do not
+					 * decode catalog changes anyway. Normally such tuples
+					 * would be skipped over below, but we can't identify
+					 * whether the table should be logically logged without
+					 * mapping the relfilenode to the oid.
+					 */
+					if (reloid == InvalidOid &&
+						change->data.tp.newtuple == NULL &&
+						change->data.tp.oldtuple == NULL)
+						goto change_done;
+					else if (reloid == InvalidOid)
+						elog(ERROR, "could not map filenode \"%s\" to relation OID",
+							 relpathperm(change->data.tp.relnode,
+										 MAIN_FORKNUM));
+
+					relation = RelationIdGetRelation(reloid);
+
+					if (!RelationIsValid(relation))
+						elog(ERROR, "could not open relation with OID %u (for filenode \"%s\")",
+							 reloid,
+							 relpathperm(change->data.tp.relnode,
+										 MAIN_FORKNUM));
+
+					if (!RelationIsLogicallyLogged(relation))
+						goto change_done;
+
+					/*
+					 * Ignore temporary heaps created during DDL unless the
+					 * plugin has asked for them.
+					 */
+					if (relation->rd_rel->relrewrite && !rb->output_rewrites)
+						goto change_done;
+
+					/*
+					 * For now ignore sequence changes entirely. Most of the
+					 * time they don't log changes using records we
+					 * understand, so it doesn't make sense to handle the few
+					 * cases we do.
+					 */
+					if (relation->rd_rel->relkind == RELKIND_SEQUENCE)
+						goto change_done;
+
+					/* user-triggered change */
+					if (!IsToastRelation(relation))
+					{
+						ReorderBufferToastReplace(rb, txn, relation, change);
+						ReorderBufferApplyChange(rb, txn, relation, change,
+												 streaming);
+
+						/*
+						 * Only clear reassembled toast chunks if we're sure
+						 * they're not required anymore. The creator of the
+						 * tuple tells us.
+						 */
+						if (change->data.tp.clear_toast_afterwards)
+							ReorderBufferToastReset(rb, txn);
+					}
+					/* we're not interested in toast deletions */
+					else if (change->action == REORDER_BUFFER_CHANGE_INSERT)
+					{
+						/*
+						 * Need to reassemble the full toasted Datum in
+						 * memory, to ensure the chunks don't get reused till
+						 * we're done remove it from the list of this
+						 * transaction's changes. Otherwise it will get
+						 * freed/reused while restoring spooled data from
+						 * disk.
+						 */
+						Assert(change->data.tp.newtuple != NULL);
+
+						dlist_delete(&change->node);
+						ReorderBufferToastAppendChunk(rb, txn, relation,
+													  change);
+					}
+
+			change_done:
+
+					/*
+					 * If speculative insertion was confirmed, the record
+					 * isn't needed anymore.
+					 */
+					if (specinsert != NULL)
+					{
+						ReorderBufferReturnChange(rb, specinsert, true);
+						specinsert = NULL;
+					}
+
+					if (RelationIsValid(relation))
+					{
+						RelationClose(relation);
+						relation = NULL;
+					}
+					break;
+
+				case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
+
+					/*
+					 * Speculative insertions are dealt with by delaying the
+					 * processing of the insert until the confirmation record
+					 * arrives. For that we simply unlink the record from the
+					 * chain, so it does not get freed/reused while restoring
+					 * spooled data from disk.
+					 *
+					 * This is safe in the face of concurrent catalog changes
+					 * because the relevant relation can't be changed between
+					 * speculative insertion and confirmation due to
+					 * CheckTableNotInUse() and locking.
+					 */
+
+					/* clear out a pending (and thus failed) speculation */
+					if (specinsert != NULL)
+					{
+						ReorderBufferReturnChange(rb, specinsert, true);
+						specinsert = NULL;
+					}
+
+					/* and memorize the pending insertion */
+					dlist_delete(&change->node);
+					specinsert = change;
+					break;
+
+				case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
+
+					/*
+					 * Abort for speculative insertion arrived. So cleanup the
+					 * specinsert tuple and toast hash.
+					 *
+					 * Note that we get the spec abort change for each toast
+					 * entry but we need to perform the cleanup only the first
+					 * time we get it for the main table.
+					 */
+					if (specinsert != NULL)
+					{
+						/*
+						 * We must clean the toast hash before processing a
+						 * completely new tuple to avoid confusion about the
+						 * previous tuple's toast chunks.
+						 */
+						Assert(change->data.tp.clear_toast_afterwards);
+						ReorderBufferToastReset(rb, txn);
+
+						/* We don't need this record anymore. */
+						ReorderBufferReturnChange(rb, specinsert, true);
+						specinsert = NULL;
+					}
+					break;
+
+				case REORDER_BUFFER_CHANGE_TRUNCATE:
+					{
+						int			i;
+						int			nrelids = change->data.truncate.nrelids;
+						int			nrelations = 0;
+						Relation   *relations;
+
+						relations = palloc0(nrelids * sizeof(Relation));
+						for (i = 0; i < nrelids; i++)
+						{
+							Oid			relid = change->data.truncate.relids[i];
+							Relation	relation;
+
+							relation = RelationIdGetRelation(relid);
+
+							if (!RelationIsValid(relation))
+								elog(ERROR, "could not open relation with OID %u", relid);
+
+							if (!RelationIsLogicallyLogged(relation))
+								continue;
+
+							relations[nrelations++] = relation;
+						}
+
+						/* Apply the truncate. */
+						ReorderBufferApplyTruncate(rb, txn, nrelations,
+												   relations, change,
+												   streaming);
+
+						for (i = 0; i < nrelations; i++)
+							RelationClose(relations[i]);
+
+						break;
+					}
+
+				case REORDER_BUFFER_CHANGE_MESSAGE:
+					ReorderBufferApplyMessage(rb, txn, change, streaming);
+					break;
+
+				case REORDER_BUFFER_CHANGE_INVALIDATION:
+					/* Execute the invalidation messages locally */
+					ReorderBufferExecuteInvalidations(
+													  change->data.inval.ninvalidations,
+													  change->data.inval.invalidations);
+					break;
+
+				case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
+					/* get rid of the old */
+					TeardownHistoricSnapshot(false);
+
+					if (snapshot_now->copied)
+					{
+						ReorderBufferFreeSnap(rb, snapshot_now);
+						snapshot_now =
+							ReorderBufferCopySnap(rb, change->data.snapshot,
+												  txn, command_id);
+					}
+
+					/*
+					 * Restored from disk, need to be careful not to double
+					 * free. We could introduce refcounting for that, but for
+					 * now this seems infrequent enough not to care.
+					 */
+					else if (change->data.snapshot->copied)
+					{
+						snapshot_now =
+							ReorderBufferCopySnap(rb, change->data.snapshot,
+												  txn, command_id);
+					}
+					else
+					{
+						snapshot_now = change->data.snapshot;
+					}
+
+					/* and continue with the new one */
+					SetupHistoricSnapshot(snapshot_now, txn->tuplecid_hash);
+					break;
+
+				case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
+					Assert(change->data.command_id != InvalidCommandId);
+
+					if (command_id < change->data.command_id)
+					{
+						command_id = change->data.command_id;
+
+						if (!snapshot_now->copied)
+						{
+							/* we don't use the global one anymore */
+							snapshot_now = ReorderBufferCopySnap(rb, snapshot_now,
+																 txn, command_id);
+						}
+
+						snapshot_now->curcid = command_id;
+
+						TeardownHistoricSnapshot(false);
+						SetupHistoricSnapshot(snapshot_now, txn->tuplecid_hash);
+					}
+
+					break;
+
+				case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
+					elog(ERROR, "tuplecid value in changequeue");
+					break;
+			}
+		}
+
+		/* speculative insertion record must be freed by now */
+		Assert(!specinsert);
+
+		/* clean up the iterator */
+		ReorderBufferIterTXNFinish(rb, iterstate);
+		iterstate = NULL;
+
+		/*
+		 * Update total transaction count and total bytes processed by the
+		 * transaction and its subtransactions. Ensure to not count the
+		 * streamed transaction multiple times.
+		 *
+		 * Note that the statistics computation has to be done after
+		 * ReorderBufferIterTXNFinish as it releases the serialized change
+		 * which we have already accounted in ReorderBufferIterTXNNext.
+		 */
+		if (!rbtxn_is_streamed(txn))
+			rb->totalTxns++;
+
+		rb->totalBytes += txn->total_size;
+
+		/*
+		 * Done with current changes, send the last message for this set of
+		 * changes depending upon streaming mode.
+		 */
+		if (streaming)
+		{
+			if (stream_started)
+			{
+				rb->stream_stop(rb, txn, prev_lsn);
+				stream_started = false;
+			}
+		}
+		else
+		{
+			/*
+			 * Call either PREPARE (for two-phase transactions) or COMMIT (for
+			 * regular ones).
+			 */
+			if (rbtxn_prepared(txn))
+				rb->prepare(rb, txn, commit_lsn);
+			else
+				rb->commit(rb, txn, commit_lsn);
+		}
+
+		/* this is just a sanity check against bad output plugin behaviour */
+		if (GetCurrentTransactionIdIfAny() != InvalidTransactionId)
+			elog(ERROR, "output plugin used XID %u",
+				 GetCurrentTransactionId());
+
+		/*
+		 * Remember the command ID and snapshot for the next set of changes in
+		 * streaming mode.
+		 */
+		if (streaming)
+			ReorderBufferSaveTXNSnapshot(rb, txn, snapshot_now, command_id);
+		else if (snapshot_now->copied)
+			ReorderBufferFreeSnap(rb, snapshot_now);
+
+		/* cleanup */
+		TeardownHistoricSnapshot(false);
+
+		/*
+		 * Aborting the current (sub-)transaction as a whole has the right
+		 * semantics. We want all locks acquired in here to be released, not
+		 * reassigned to the parent and we do not want any database access
+		 * have persistent effects.
+		 */
+		AbortCurrentTransaction();
+
+		/* make sure there's no cache pollution */
+		ReorderBufferExecuteInvalidations(txn->ninvalidations, txn->invalidations);
+
+		if (using_subtxn)
+			RollbackAndReleaseCurrentSubTransaction();
+
+		/*
+		 * We are here due to one of the four reasons: 1. Decoding an
+		 * in-progress txn. 2. Decoding a prepared txn. 3. Decoding of a
+		 * prepared txn that was (partially) streamed. 4. Decoding a committed
+		 * txn.
+		 *
+		 * For 1, we allow truncation of txn data by removing the changes
+		 * already streamed but still keeping other things like invalidations,
+		 * snapshot, and tuplecids. For 2 and 3, we indicate
+		 * ReorderBufferTruncateTXN to do more elaborate truncation of txn
+		 * data as the entire transaction has been decoded except for commit.
+		 * For 4, as the entire txn has been decoded, we can fully clean up
+		 * the TXN reorder buffer.
+		 */
+		if (streaming || rbtxn_prepared(txn))
+		{
+			ReorderBufferTruncateTXN(rb, txn, rbtxn_prepared(txn));
+			/* Reset the CheckXidAlive */
+			CheckXidAlive = InvalidTransactionId;
+		}
+		else
+			ReorderBufferCleanupTXN(rb, txn);
+	}
+	PG_CATCH();
+	{
+		MemoryContext ecxt = MemoryContextSwitchTo(ccxt);
+		ErrorData  *errdata = CopyErrorData();
+
+		/* TODO: Encapsulate cleanup from the PG_TRY and PG_CATCH blocks */
+		if (iterstate)
+			ReorderBufferIterTXNFinish(rb, iterstate);
+
+		TeardownHistoricSnapshot(true);
+
+		/*
+		 * Force cache invalidation to happen outside of a valid transaction
+		 * to prevent catalog access as we just caught an error.
+		 */
+		AbortCurrentTransaction();
+
+		/* make sure there's no cache pollution */
+		ReorderBufferExecuteInvalidations(txn->ninvalidations,
+										  txn->invalidations);
+
+		if (using_subtxn)
+			RollbackAndReleaseCurrentSubTransaction();
+
+		/*
+		 * The error code ERRCODE_TRANSACTION_ROLLBACK indicates a concurrent
+		 * abort of the (sub)transaction we are streaming or preparing. We
+		 * need to do the cleanup and return gracefully on this error, see
+		 * SetupCheckXidLive.
+		 *
+		 * This error code can be thrown by one of the callbacks we call
+		 * during decoding so we need to ensure that we return gracefully only
+		 * when we are sending the data in streaming mode and the streaming is
+		 * not finished yet or when we are sending the data out on a PREPARE
+		 * during a two-phase commit.
+		 */
+		if (errdata->sqlerrcode == ERRCODE_TRANSACTION_ROLLBACK &&
+			(stream_started || rbtxn_prepared(txn)))
+		{
+			/* curtxn must be set for streaming or prepared transactions */
+			Assert(curtxn);
+
+			/* Cleanup the temporary error state. */
+			FlushErrorState();
+			FreeErrorData(errdata);
+			errdata = NULL;
+			curtxn->concurrent_abort = true;
+
+			/* Reset the TXN so that it is allowed to stream remaining data. */
+			ReorderBufferResetTXN(rb, txn, snapshot_now,
+								  command_id, prev_lsn,
+								  specinsert);
+		}
+		else
+		{
+			ReorderBufferCleanupTXN(rb, txn);
+			MemoryContextSwitchTo(ecxt);
+			PG_RE_THROW();
+		}
+	}
+	PG_END_TRY();
+}
+
+/*
+ * Perform the replay of a transaction and its non-aborted subtransactions.
+ *
+ * Subtransactions previously have to be processed by
+ * ReorderBufferCommitChild(), even if previously assigned to the toplevel
+ * transaction with ReorderBufferAssignChild.
+ *
+ * This interface is called once a prepare or toplevel commit is read for both
+ * streamed as well as non-streamed transactions.
+ */
+static void
+ReorderBufferReplay(ReorderBufferTXN *txn,
+					ReorderBuffer *rb, TransactionId xid,
+					XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
+					TimestampTz commit_time,
+					RepOriginId origin_id, XLogRecPtr origin_lsn)
+{
+	Snapshot	snapshot_now;
+	CommandId	command_id = FirstCommandId;
+
+	txn->final_lsn = commit_lsn;
+	txn->end_lsn = end_lsn;
+	txn->commit_time = commit_time;
+	txn->origin_id = origin_id;
+	txn->origin_lsn = origin_lsn;
+
+	/*
+	 * If the transaction was (partially) streamed, we need to commit it in a
+	 * 'streamed' way. That is, we first stream the remaining part of the
+	 * transaction, and then invoke stream_commit message.
+	 *
+	 * Called after everything (origin ID, LSN, ...) is stored in the
+	 * transaction to avoid passing that information directly.
+	 */
+	if (rbtxn_is_streamed(txn))
+	{
+		ReorderBufferStreamCommit(rb, txn);
+		return;
+	}
+
+	/*
+	 * If this transaction has no snapshot, it didn't make any changes to the
+	 * database, so there's nothing to decode.  Note that
+	 * ReorderBufferCommitChild will have transferred any snapshots from
+	 * subtransactions if there were any.
+	 */
+	if (txn->base_snapshot == NULL)
+	{
+		Assert(txn->ninvalidations == 0);
+
+		/*
+		 * Removing this txn before a commit might result in the computation
+		 * of an incorrect restart_lsn. See SnapBuildProcessRunningXacts.
+		 */
+		if (!rbtxn_prepared(txn))
+			ReorderBufferCleanupTXN(rb, txn);
+		return;
+	}
+
+	snapshot_now = txn->base_snapshot;
+
+	/* Process and send the changes to output plugin. */
+	ReorderBufferProcessTXN(rb, txn, commit_lsn, snapshot_now,
+							command_id, false);
+}
+
+/*
+ * Commit a transaction.
+ *
+ * See comments for ReorderBufferReplay().
+ */
+void
+ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
+					XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
+					TimestampTz commit_time,
+					RepOriginId origin_id, XLogRecPtr origin_lsn)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
+								false);
+
+	/* unknown transaction, nothing to replay */
+	if (txn == NULL)
+		return;
+
+	ReorderBufferReplay(txn, rb, xid, commit_lsn, end_lsn, commit_time,
+						origin_id, origin_lsn);
+}
+
+/*
+ * Record the prepare information for a transaction.
+ */
+bool
+ReorderBufferRememberPrepareInfo(ReorderBuffer *rb, TransactionId xid,
+								 XLogRecPtr prepare_lsn, XLogRecPtr end_lsn,
+								 TimestampTz prepare_time,
+								 RepOriginId origin_id, XLogRecPtr origin_lsn)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr, false);
+
+	/* unknown transaction, nothing to do */
+	if (txn == NULL)
+		return false;
+
+	/*
+	 * Remember the prepare information to be later used by commit prepared in
+	 * case we skip doing prepare.
+	 */
+	txn->final_lsn = prepare_lsn;
+	txn->end_lsn = end_lsn;
+	txn->commit_time = prepare_time;
+	txn->origin_id = origin_id;
+	txn->origin_lsn = origin_lsn;
+
+	return true;
+}
+
+/* Remember that we have skipped prepare */
+void
+ReorderBufferSkipPrepare(ReorderBuffer *rb, TransactionId xid)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr, false);
+
+	/* unknown transaction, nothing to do */
+	if (txn == NULL)
+		return;
+
+	txn->txn_flags |= RBTXN_SKIPPED_PREPARE;
+}
+
+/*
+ * Prepare a two-phase transaction.
+ *
+ * See comments for ReorderBufferReplay().
+ */
+void
+ReorderBufferPrepare(ReorderBuffer *rb, TransactionId xid,
+					 char *gid)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
+								false);
+
+	/* unknown transaction, nothing to replay */
+	if (txn == NULL)
+		return;
+
+	txn->txn_flags |= RBTXN_PREPARE;
+	txn->gid = pstrdup(gid);
+
+	/* The prepare info must have been updated in txn by now. */
+	Assert(txn->final_lsn != InvalidXLogRecPtr);
+
+	ReorderBufferReplay(txn, rb, xid, txn->final_lsn, txn->end_lsn,
+						txn->commit_time, txn->origin_id, txn->origin_lsn);
+
+	/*
+	 * We send the prepare for the concurrently aborted xacts so that later
+	 * when rollback prepared is decoded and sent, the downstream should be
+	 * able to rollback such a xact. See comments atop DecodePrepare.
+	 *
+	 * Note, for the concurrent_abort + streaming case a stream_prepare was
+	 * already sent within the ReorderBufferReplay call above.
+	 */
+	if (txn->concurrent_abort && !rbtxn_is_streamed(txn))
+		rb->prepare(rb, txn, txn->final_lsn);
+}
+
+/*
+ * This is used to handle COMMIT/ROLLBACK PREPARED.
+ */
+void
+ReorderBufferFinishPrepared(ReorderBuffer *rb, TransactionId xid,
+							XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
+							XLogRecPtr initial_consistent_point,
+							TimestampTz commit_time, RepOriginId origin_id,
+							XLogRecPtr origin_lsn, char *gid, bool is_commit)
+{
+	ReorderBufferTXN *txn;
+	XLogRecPtr	prepare_end_lsn;
+	TimestampTz prepare_time;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, commit_lsn, false);
+
+	/* unknown transaction, nothing to do */
+	if (txn == NULL)
+		return;
+
+	/*
+	 * By this time the txn has the prepare record information, remember it to
+	 * be later used for rollback.
+	 */
+	prepare_end_lsn = txn->end_lsn;
+	prepare_time = txn->commit_time;
+
+	/* add the gid in the txn */
+	txn->gid = pstrdup(gid);
+
+	/*
+	 * It is possible that this transaction is not decoded at prepare time
+	 * either because by that time we didn't have a consistent snapshot or it
+	 * was decoded earlier but we have restarted. We only need to send the
+	 * prepare if it was not decoded earlier. We don't need to decode the xact
+	 * for aborts if it is not done already.
+	 */
+	if ((txn->final_lsn < initial_consistent_point) && is_commit)
+	{
+		txn->txn_flags |= RBTXN_PREPARE;
+
+		/*
+		 * The prepare info must have been updated in txn even if we skip
+		 * prepare.
+		 */
+		Assert(txn->final_lsn != InvalidXLogRecPtr);
+
+		/*
+		 * By this time the txn has the prepare record information and it is
+		 * important to use that so that downstream gets the accurate
+		 * information. If instead, we have passed commit information here
+		 * then downstream can behave as it has already replayed commit
+		 * prepared after the restart.
+		 */
+		ReorderBufferReplay(txn, rb, xid, txn->final_lsn, txn->end_lsn,
+							txn->commit_time, txn->origin_id, txn->origin_lsn);
+	}
+
+	txn->final_lsn = commit_lsn;
+	txn->end_lsn = end_lsn;
+	txn->commit_time = commit_time;
+	txn->origin_id = origin_id;
+	txn->origin_lsn = origin_lsn;
+
+	if (is_commit)
+		rb->commit_prepared(rb, txn, commit_lsn);
+	else
+		rb->rollback_prepared(rb, txn, prepare_end_lsn, prepare_time);
+
+	/* cleanup: make sure there's no cache pollution */
+	ReorderBufferExecuteInvalidations(txn->ninvalidations,
+									  txn->invalidations);
+	ReorderBufferCleanupTXN(rb, txn);
+}
+
+/*
+ * Abort a transaction that possibly has previous changes. Needs to be first
+ * called for subtransactions and then for the toplevel xid.
+ *
+ * NB: Transactions handled here have to have actively aborted (i.e. have
+ * produced an abort record). Implicitly aborted transactions are handled via
+ * ReorderBufferAbortOld(); transactions we're just not interested in, but
+ * which have committed are handled in ReorderBufferForget().
+ *
+ * This function purges this transaction and its contents from memory and
+ * disk.
+ */
+void
+ReorderBufferAbort(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
+								false);
+
+	/* unknown, nothing to remove */
+	if (txn == NULL)
+		return;
+
+	/* For streamed transactions notify the remote node about the abort. */
+	if (rbtxn_is_streamed(txn))
+	{
+		rb->stream_abort(rb, txn, lsn);
+
+		/*
+		 * We might have decoded changes for this transaction that could load
+		 * the cache as per the current transaction's view (consider DDL's
+		 * happened in this transaction). We don't want the decoding of future
+		 * transactions to use those cache entries so execute invalidations.
+		 */
+		if (txn->ninvalidations > 0)
+			ReorderBufferImmediateInvalidation(rb, txn->ninvalidations,
+											   txn->invalidations);
+	}
+
+	/* cosmetic... */
+	txn->final_lsn = lsn;
+
+	/* remove potential on-disk data, and deallocate */
+	ReorderBufferCleanupTXN(rb, txn);
+}
+
+/*
+ * Abort all transactions that aren't actually running anymore because the
+ * server restarted.
+ *
+ * NB: These really have to be transactions that have aborted due to a server
+ * crash/immediate restart, as we don't deal with invalidations here.
+ */
+void
+ReorderBufferAbortOld(ReorderBuffer *rb, TransactionId oldestRunningXid)
+{
+	dlist_mutable_iter it;
+
+	/*
+	 * Iterate through all (potential) toplevel TXNs and abort all that are
+	 * older than what possibly can be running. Once we've found the first
+	 * that is alive we stop, there might be some that acquired an xid earlier
+	 * but started writing later, but it's unlikely and they will be cleaned
+	 * up in a later call to this function.
+	 */
+	dlist_foreach_modify(it, &rb->toplevel_by_lsn)
+	{
+		ReorderBufferTXN *txn;
+
+		txn = dlist_container(ReorderBufferTXN, node, it.cur);
+
+		if (TransactionIdPrecedes(txn->xid, oldestRunningXid))
+		{
+			elog(DEBUG2, "aborting old transaction %u", txn->xid);
+
+			/* remove potential on-disk data, and deallocate this tx */
+			ReorderBufferCleanupTXN(rb, txn);
+		}
+		else
+			return;
+	}
+}
+
+/*
+ * Forget the contents of a transaction if we aren't interested in its
+ * contents. Needs to be first called for subtransactions and then for the
+ * toplevel xid.
+ *
+ * This is significantly different to ReorderBufferAbort() because
+ * transactions that have committed need to be treated differently from aborted
+ * ones since they may have modified the catalog.
+ *
+ * Note that this is only allowed to be called in the moment a transaction
+ * commit has just been read, not earlier; otherwise later records referring
+ * to this xid might re-create the transaction incompletely.
+ */
+void
+ReorderBufferForget(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
+								false);
+
+	/* unknown, nothing to forget */
+	if (txn == NULL)
+		return;
+
+	/* For streamed transactions notify the remote node about the abort. */
+	if (rbtxn_is_streamed(txn))
+		rb->stream_abort(rb, txn, lsn);
+
+	/* cosmetic... */
+	txn->final_lsn = lsn;
+
+	/*
+	 * Process cache invalidation messages if there are any. Even if we're not
+	 * interested in the transaction's contents, it could have manipulated the
+	 * catalog and we need to update the caches according to that.
+	 */
+	if (txn->base_snapshot != NULL && txn->ninvalidations > 0)
+		ReorderBufferImmediateInvalidation(rb, txn->ninvalidations,
+										   txn->invalidations);
+	else
+		Assert(txn->ninvalidations == 0);
+
+	/* remove potential on-disk data, and deallocate */
+	ReorderBufferCleanupTXN(rb, txn);
+}
+
+/*
+ * Invalidate cache for those transactions that need to be skipped just in case
+ * catalogs were manipulated as part of the transaction.
+ *
+ * Note that this is a special-purpose function for prepared transactions where
+ * we don't want to clean up the TXN even when we decide to skip it. See
+ * DecodePrepare.
+ */
+void
+ReorderBufferInvalidate(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
+								false);
+
+	/* unknown, nothing to do */
+	if (txn == NULL)
+		return;
+
+	/*
+	 * Process cache invalidation messages if there are any. Even if we're not
+	 * interested in the transaction's contents, it could have manipulated the
+	 * catalog and we need to update the caches according to that.
+	 */
+	if (txn->base_snapshot != NULL && txn->ninvalidations > 0)
+		ReorderBufferImmediateInvalidation(rb, txn->ninvalidations,
+										   txn->invalidations);
+	else
+		Assert(txn->ninvalidations == 0);
+}
+
+
+/*
+ * Execute invalidations happening outside the context of a decoded
+ * transaction. That currently happens either for xid-less commits
+ * (cf. RecordTransactionCommit()) or for invalidations in uninteresting
+ * transactions (via ReorderBufferForget()).
+ */
+void
+ReorderBufferImmediateInvalidation(ReorderBuffer *rb, uint32 ninvalidations,
+								   SharedInvalidationMessage *invalidations)
+{
+	bool		use_subtxn = IsTransactionOrTransactionBlock();
+	int			i;
+
+	if (use_subtxn)
+		BeginInternalSubTransaction("replay");
+
+	/*
+	 * Force invalidations to happen outside of a valid transaction - that way
+	 * entries will just be marked as invalid without accessing the catalog.
+	 * That's advantageous because we don't need to setup the full state
+	 * necessary for catalog access.
+	 */
+	if (use_subtxn)
+		AbortCurrentTransaction();
+
+	for (i = 0; i < ninvalidations; i++)
+		LocalExecuteInvalidationMessage(&invalidations[i]);
+
+	if (use_subtxn)
+		RollbackAndReleaseCurrentSubTransaction();
+}
+
+/*
+ * Tell reorderbuffer about an xid seen in the WAL stream. Has to be called at
+ * least once for every xid in XLogRecord->xl_xid (other places in records
+ * may, but do not have to be passed through here).
+ *
+ * Reorderbuffer keeps some datastructures about transactions in LSN order,
+ * for efficiency. To do that it has to know about when transactions are seen
+ * first in the WAL. As many types of records are not actually interesting for
+ * logical decoding, they do not necessarily pass though here.
+ */
+void
+ReorderBufferProcessXid(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
+{
+	/* many records won't have an xid assigned, centralize check here */
+	if (xid != InvalidTransactionId)
+		ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+}
+
+/*
+ * Add a new snapshot to this transaction that may only used after lsn 'lsn'
+ * because the previous snapshot doesn't describe the catalog correctly for
+ * following rows.
+ */
+void
+ReorderBufferAddSnapshot(ReorderBuffer *rb, TransactionId xid,
+						 XLogRecPtr lsn, Snapshot snap)
+{
+	ReorderBufferChange *change = ReorderBufferGetChange(rb);
+
+	change->data.snapshot = snap;
+	change->action = REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT;
+
+	ReorderBufferQueueChange(rb, xid, lsn, change, false);
+}
+
+/*
+ * Set up the transaction's base snapshot.
+ *
+ * If we know that xid is a subtransaction, set the base snapshot on the
+ * top-level transaction instead.
+ */
+void
+ReorderBufferSetBaseSnapshot(ReorderBuffer *rb, TransactionId xid,
+							 XLogRecPtr lsn, Snapshot snap)
+{
+	ReorderBufferTXN *txn;
+	bool		is_new;
+
+	AssertArg(snap != NULL);
+
+	/*
+	 * Fetch the transaction to operate on.  If we know it's a subtransaction,
+	 * operate on its top-level transaction instead.
+	 */
+	txn = ReorderBufferTXNByXid(rb, xid, true, &is_new, lsn, true);
+	if (rbtxn_is_known_subxact(txn))
+		txn = ReorderBufferTXNByXid(rb, txn->toplevel_xid, false,
+									NULL, InvalidXLogRecPtr, false);
+	Assert(txn->base_snapshot == NULL);
+
+	txn->base_snapshot = snap;
+	txn->base_snapshot_lsn = lsn;
+	dlist_push_tail(&rb->txns_by_base_snapshot_lsn, &txn->base_snapshot_node);
+
+	AssertTXNLsnOrder(rb);
+}
+
+/*
+ * Access the catalog with this CommandId at this point in the changestream.
+ *
+ * May only be called for command ids > 1
+ */
+void
+ReorderBufferAddNewCommandId(ReorderBuffer *rb, TransactionId xid,
+							 XLogRecPtr lsn, CommandId cid)
+{
+	ReorderBufferChange *change = ReorderBufferGetChange(rb);
+
+	change->data.command_id = cid;
+	change->action = REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID;
+
+	ReorderBufferQueueChange(rb, xid, lsn, change, false);
+}
+
+/*
+ * Update memory counters to account for the new or removed change.
+ *
+ * We update two counters - in the reorder buffer, and in the transaction
+ * containing the change. The reorder buffer counter allows us to quickly
+ * decide if we reached the memory limit, the transaction counter allows
+ * us to quickly pick the largest transaction for eviction.
+ *
+ * When streaming is enabled, we need to update the toplevel transaction
+ * counters instead - we don't really care about subtransactions as we
+ * can't stream them individually anyway, and we only pick toplevel
+ * transactions for eviction. So only toplevel transactions matter.
+ */
+static void
+ReorderBufferChangeMemoryUpdate(ReorderBuffer *rb,
+								ReorderBufferChange *change,
+								bool addition, Size sz)
+{
+	ReorderBufferTXN *txn;
+	ReorderBufferTXN *toptxn;
+
+	Assert(change->txn);
+
+	/*
+	 * Ignore tuple CID changes, because those are not evicted when reaching
+	 * memory limit. So we just don't count them, because it might easily
+	 * trigger a pointless attempt to spill.
+	 */
+	if (change->action == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID)
+		return;
+
+	txn = change->txn;
+
+	/*
+	 * Update the total size in top level as well. This is later used to
+	 * compute the decoding stats.
+	 */
+	if (txn->toptxn != NULL)
+		toptxn = txn->toptxn;
+	else
+		toptxn = txn;
+
+	if (addition)
+	{
+		txn->size += sz;
+		rb->size += sz;
+
+		/* Update the total size in the top transaction. */
+		toptxn->total_size += sz;
+	}
+	else
+	{
+		Assert((rb->size >= sz) && (txn->size >= sz));
+		txn->size -= sz;
+		rb->size -= sz;
+
+		/* Update the total size in the top transaction. */
+		toptxn->total_size -= sz;
+	}
+
+	Assert(txn->size <= rb->size);
+}
+
+/*
+ * Add new (relfilenode, tid) -> (cmin, cmax) mappings.
+ *
+ * We do not include this change type in memory accounting, because we
+ * keep CIDs in a separate list and do not evict them when reaching
+ * the memory limit.
+ */
+void
+ReorderBufferAddNewTupleCids(ReorderBuffer *rb, TransactionId xid,
+							 XLogRecPtr lsn, RelFileNode node,
+							 ItemPointerData tid, CommandId cmin,
+							 CommandId cmax, CommandId combocid)
+{
+	ReorderBufferChange *change = ReorderBufferGetChange(rb);
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+	change->data.tuplecid.node = node;
+	change->data.tuplecid.tid = tid;
+	change->data.tuplecid.cmin = cmin;
+	change->data.tuplecid.cmax = cmax;
+	change->data.tuplecid.combocid = combocid;
+	change->lsn = lsn;
+	change->txn = txn;
+	change->action = REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID;
+
+	dlist_push_tail(&txn->tuplecids, &change->node);
+	txn->ntuplecids++;
+}
+
+/*
+ * Setup the invalidation of the toplevel transaction.
+ *
+ * This needs to be called for each XLOG_XACT_INVALIDATIONS message and
+ * accumulates all the invalidation messages in the toplevel transaction as
+ * well as in the form of change in reorder buffer.  We require to record it in
+ * form of the change so that we can execute only the required invalidations
+ * instead of executing all the invalidations on each CommandId increment.  We
+ * also need to accumulate these in the toplevel transaction because in some
+ * cases we skip processing the transaction (see ReorderBufferForget), we need
+ * to execute all the invalidations together.
+ */
+void
+ReorderBufferAddInvalidations(ReorderBuffer *rb, TransactionId xid,
+							  XLogRecPtr lsn, Size nmsgs,
+							  SharedInvalidationMessage *msgs)
+{
+	ReorderBufferTXN *txn;
+	MemoryContext oldcontext;
+	ReorderBufferChange *change;
+
+	txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+	oldcontext = MemoryContextSwitchTo(rb->context);
+
+	/*
+	 * Collect all the invalidations under the top transaction so that we can
+	 * execute them all together.  See comment atop this function
+	 */
+	if (txn->toptxn)
+		txn = txn->toptxn;
+
+	Assert(nmsgs > 0);
+
+	/* Accumulate invalidations. */
+	if (txn->ninvalidations == 0)
+	{
+		txn->ninvalidations = nmsgs;
+		txn->invalidations = (SharedInvalidationMessage *)
+			palloc(sizeof(SharedInvalidationMessage) * nmsgs);
+		memcpy(txn->invalidations, msgs,
+			   sizeof(SharedInvalidationMessage) * nmsgs);
+	}
+	else
+	{
+		txn->invalidations = (SharedInvalidationMessage *)
+			repalloc(txn->invalidations, sizeof(SharedInvalidationMessage) *
+					 (txn->ninvalidations + nmsgs));
+
+		memcpy(txn->invalidations + txn->ninvalidations, msgs,
+			   nmsgs * sizeof(SharedInvalidationMessage));
+		txn->ninvalidations += nmsgs;
+	}
+
+	change = ReorderBufferGetChange(rb);
+	change->action = REORDER_BUFFER_CHANGE_INVALIDATION;
+	change->data.inval.ninvalidations = nmsgs;
+	change->data.inval.invalidations = (SharedInvalidationMessage *)
+		palloc(sizeof(SharedInvalidationMessage) * nmsgs);
+	memcpy(change->data.inval.invalidations, msgs,
+		   sizeof(SharedInvalidationMessage) * nmsgs);
+
+	ReorderBufferQueueChange(rb, xid, lsn, change, false);
+
+	MemoryContextSwitchTo(oldcontext);
+}
+
+/*
+ * Apply all invalidations we know. Possibly we only need parts at this point
+ * in the changestream but we don't know which those are.
+ */
+static void
+ReorderBufferExecuteInvalidations(uint32 nmsgs, SharedInvalidationMessage *msgs)
+{
+	int			i;
+
+	for (i = 0; i < nmsgs; i++)
+		LocalExecuteInvalidationMessage(&msgs[i]);
+}
+
+/*
+ * Mark a transaction as containing catalog changes
+ */
+void
+ReorderBufferXidSetCatalogChanges(ReorderBuffer *rb, TransactionId xid,
+								  XLogRecPtr lsn)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+	txn->txn_flags |= RBTXN_HAS_CATALOG_CHANGES;
+
+	/*
+	 * Mark top-level transaction as having catalog changes too if one of its
+	 * children has so that the ReorderBufferBuildTupleCidHash can
+	 * conveniently check just top-level transaction and decide whether to
+	 * build the hash table or not.
+	 */
+	if (txn->toptxn != NULL)
+		txn->toptxn->txn_flags |= RBTXN_HAS_CATALOG_CHANGES;
+}
+
+/*
+ * Query whether a transaction is already *known* to contain catalog
+ * changes. This can be wrong until directly before the commit!
+ */
+bool
+ReorderBufferXidHasCatalogChanges(ReorderBuffer *rb, TransactionId xid)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
+								false);
+	if (txn == NULL)
+		return false;
+
+	return rbtxn_has_catalog_changes(txn);
+}
+
+/*
+ * ReorderBufferXidHasBaseSnapshot
+ *		Have we already set the base snapshot for the given txn/subtxn?
+ */
+bool
+ReorderBufferXidHasBaseSnapshot(ReorderBuffer *rb, TransactionId xid)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false,
+								NULL, InvalidXLogRecPtr, false);
+
+	/* transaction isn't known yet, ergo no snapshot */
+	if (txn == NULL)
+		return false;
+
+	/* a known subtxn? operate on top-level txn instead */
+	if (rbtxn_is_known_subxact(txn))
+		txn = ReorderBufferTXNByXid(rb, txn->toplevel_xid, false,
+									NULL, InvalidXLogRecPtr, false);
+
+	return txn->base_snapshot != NULL;
+}
+
+
+/*
+ * ---------------------------------------
+ * Disk serialization support
+ * ---------------------------------------
+ */
+
+/*
+ * Ensure the IO buffer is >= sz.
+ */
+static void
+ReorderBufferSerializeReserve(ReorderBuffer *rb, Size sz)
+{
+	if (!rb->outbufsize)
+	{
+		rb->outbuf = MemoryContextAlloc(rb->context, sz);
+		rb->outbufsize = sz;
+	}
+	else if (rb->outbufsize < sz)
+	{
+		rb->outbuf = repalloc(rb->outbuf, sz);
+		rb->outbufsize = sz;
+	}
+}
+
+/*
+ * Find the largest transaction (toplevel or subxact) to evict (spill to disk).
+ *
+ * XXX With many subtransactions this might be quite slow, because we'll have
+ * to walk through all of them. There are some options how we could improve
+ * that: (a) maintain some secondary structure with transactions sorted by
+ * amount of changes, (b) not looking for the entirely largest transaction,
+ * but e.g. for transaction using at least some fraction of the memory limit,
+ * and (c) evicting multiple transactions at once, e.g. to free a given portion
+ * of the memory limit (e.g. 50%).
+ */
+static ReorderBufferTXN *
+ReorderBufferLargestTXN(ReorderBuffer *rb)
+{
+	HASH_SEQ_STATUS hash_seq;
+	ReorderBufferTXNByIdEnt *ent;
+	ReorderBufferTXN *largest = NULL;
+
+	hash_seq_init(&hash_seq, rb->by_txn);
+	while ((ent = hash_seq_search(&hash_seq)) != NULL)
+	{
+		ReorderBufferTXN *txn = ent->txn;
+
+		/* if the current transaction is larger, remember it */
+		if ((!largest) || (txn->size > largest->size))
+			largest = txn;
+	}
+
+	Assert(largest);
+	Assert(largest->size > 0);
+	Assert(largest->size <= rb->size);
+
+	return largest;
+}
+
+/*
+ * Find the largest toplevel transaction to evict (by streaming).
+ *
+ * This can be seen as an optimized version of ReorderBufferLargestTXN, which
+ * should give us the same transaction (because we don't update memory account
+ * for subtransaction with streaming, so it's always 0). But we can simply
+ * iterate over the limited number of toplevel transactions that have a base
+ * snapshot. There is no use of selecting a transaction that doesn't have base
+ * snapshot because we don't decode such transactions.
+ *
+ * Note that, we skip transactions that contains incomplete changes. There
+ * is a scope of optimization here such that we can select the largest
+ * transaction which has incomplete changes.  But that will make the code and
+ * design quite complex and that might not be worth the benefit.  If we plan to
+ * stream the transactions that contains incomplete changes then we need to
+ * find a way to partially stream/truncate the transaction changes in-memory
+ * and build a mechanism to partially truncate the spilled files.
+ * Additionally, whenever we partially stream the transaction we need to
+ * maintain the last streamed lsn and next time we need to restore from that
+ * segment and the offset in WAL.  As we stream the changes from the top
+ * transaction and restore them subtransaction wise, we need to even remember
+ * the subxact from where we streamed the last change.
+ */
+static ReorderBufferTXN *
+ReorderBufferLargestTopTXN(ReorderBuffer *rb)
+{
+	dlist_iter	iter;
+	Size		largest_size = 0;
+	ReorderBufferTXN *largest = NULL;
+
+	/* Find the largest top-level transaction having a base snapshot. */
+	dlist_foreach(iter, &rb->txns_by_base_snapshot_lsn)
+	{
+		ReorderBufferTXN *txn;
+
+		txn = dlist_container(ReorderBufferTXN, base_snapshot_node, iter.cur);
+
+		/* must not be a subtxn */
+		Assert(!rbtxn_is_known_subxact(txn));
+		/* base_snapshot must be set */
+		Assert(txn->base_snapshot != NULL);
+
+		if ((largest == NULL || txn->total_size > largest_size) &&
+			(txn->total_size > 0) && !(rbtxn_has_partial_change(txn)))
+		{
+			largest = txn;
+			largest_size = txn->total_size;
+		}
+	}
+
+	return largest;
+}
+
+/*
+ * Check whether the logical_decoding_work_mem limit was reached, and if yes
+ * pick the largest (sub)transaction at-a-time to evict and spill its changes to
+ * disk until we reach under the memory limit.
+ *
+ * XXX At this point we select the transactions until we reach under the memory
+ * limit, but we might also adapt a more elaborate eviction strategy - for example
+ * evicting enough transactions to free certain fraction (e.g. 50%) of the memory
+ * limit.
+ */
+static void
+ReorderBufferCheckMemoryLimit(ReorderBuffer *rb)
+{
+	ReorderBufferTXN *txn;
+
+	/* bail out if we haven't exceeded the memory limit */
+	if (rb->size < logical_decoding_work_mem * 1024L)
+		return;
+
+	/*
+	 * Loop until we reach under the memory limit.  One might think that just
+	 * by evicting the largest (sub)transaction we will come under the memory
+	 * limit based on assumption that the selected transaction is at least as
+	 * large as the most recent change (which caused us to go over the memory
+	 * limit). However, that is not true because a user can reduce the
+	 * logical_decoding_work_mem to a smaller value before the most recent
+	 * change.
+	 */
+	while (rb->size >= logical_decoding_work_mem * 1024L)
+	{
+		/*
+		 * Pick the largest transaction (or subtransaction) and evict it from
+		 * memory by streaming, if possible.  Otherwise, spill to disk.
+		 */
+		if (ReorderBufferCanStartStreaming(rb) &&
+			(txn = ReorderBufferLargestTopTXN(rb)) != NULL)
+		{
+			/* we know there has to be one, because the size is not zero */
+			Assert(txn && !txn->toptxn);
+			Assert(txn->total_size > 0);
+			Assert(rb->size >= txn->total_size);
+
+			ReorderBufferStreamTXN(rb, txn);
+		}
+		else
+		{
+			/*
+			 * Pick the largest transaction (or subtransaction) and evict it
+			 * from memory by serializing it to disk.
+			 */
+			txn = ReorderBufferLargestTXN(rb);
+
+			/* we know there has to be one, because the size is not zero */
+			Assert(txn);
+			Assert(txn->size > 0);
+			Assert(rb->size >= txn->size);
+
+			ReorderBufferSerializeTXN(rb, txn);
+		}
+
+		/*
+		 * After eviction, the transaction should have no entries in memory,
+		 * and should use 0 bytes for changes.
+		 */
+		Assert(txn->size == 0);
+		Assert(txn->nentries_mem == 0);
+	}
+
+	/* We must be under the memory limit now. */
+	Assert(rb->size < logical_decoding_work_mem * 1024L);
+}
+
+/*
+ * Spill data of a large transaction (and its subtransactions) to disk.
+ */
+static void
+ReorderBufferSerializeTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	dlist_iter	subtxn_i;
+	dlist_mutable_iter change_i;
+	int			fd = -1;
+	XLogSegNo	curOpenSegNo = 0;
+	Size		spilled = 0;
+	Size		size = txn->size;
+
+	elog(DEBUG2, "spill %u changes in XID %u to disk",
+		 (uint32) txn->nentries_mem, txn->xid);
+
+	/* do the same to all child TXs */
+	dlist_foreach(subtxn_i, &txn->subtxns)
+	{
+		ReorderBufferTXN *subtxn;
+
+		subtxn = dlist_container(ReorderBufferTXN, node, subtxn_i.cur);
+		ReorderBufferSerializeTXN(rb, subtxn);
+	}
+
+	/* serialize changestream */
+	dlist_foreach_modify(change_i, &txn->changes)
+	{
+		ReorderBufferChange *change;
+
+		change = dlist_container(ReorderBufferChange, node, change_i.cur);
+
+		/*
+		 * store in segment in which it belongs by start lsn, don't split over
+		 * multiple segments tho
+		 */
+		if (fd == -1 ||
+			!XLByteInSeg(change->lsn, curOpenSegNo, wal_segment_size))
+		{
+			char		path[MAXPGPATH];
+
+			if (fd != -1)
+				CloseTransientFile(fd);
+
+			XLByteToSeg(change->lsn, curOpenSegNo, wal_segment_size);
+
+			/*
+			 * No need to care about TLIs here, only used during a single run,
+			 * so each LSN only maps to a specific WAL record.
+			 */
+			ReorderBufferSerializedPath(path, MyReplicationSlot, txn->xid,
+										curOpenSegNo);
+
+			/* open segment, create it if necessary */
+			fd = OpenTransientFile(path,
+								   O_CREAT | O_WRONLY | O_APPEND | PG_BINARY);
+
+			if (fd < 0)
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not open file \"%s\": %m", path)));
+		}
+
+		ReorderBufferSerializeChange(rb, txn, fd, change);
+		dlist_delete(&change->node);
+		ReorderBufferReturnChange(rb, change, true);
+
+		spilled++;
+	}
+
+	/* update the statistics iff we have spilled anything */
+	if (spilled)
+	{
+		rb->spillCount += 1;
+		rb->spillBytes += size;
+
+		/* don't consider already serialized transactions */
+		rb->spillTxns += (rbtxn_is_serialized(txn) || rbtxn_is_serialized_clear(txn)) ? 0 : 1;
+
+		/* update the decoding stats */
+		UpdateDecodingStats((LogicalDecodingContext *) rb->private_data);
+	}
+
+	Assert(spilled == txn->nentries_mem);
+	Assert(dlist_is_empty(&txn->changes));
+	txn->nentries_mem = 0;
+	txn->txn_flags |= RBTXN_IS_SERIALIZED;
+
+	if (fd != -1)
+		CloseTransientFile(fd);
+}
+
+/*
+ * Serialize individual change to disk.
+ */
+static void
+ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
+							 int fd, ReorderBufferChange *change)
+{
+	ReorderBufferDiskChange *ondisk;
+	Size		sz = sizeof(ReorderBufferDiskChange);
+
+	ReorderBufferSerializeReserve(rb, sz);
+
+	ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+	memcpy(&ondisk->change, change, sizeof(ReorderBufferChange));
+
+	switch (change->action)
+	{
+			/* fall through these, they're all similar enough */
+		case REORDER_BUFFER_CHANGE_INSERT:
+		case REORDER_BUFFER_CHANGE_UPDATE:
+		case REORDER_BUFFER_CHANGE_DELETE:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
+			{
+				char	   *data;
+				ReorderBufferTupleBuf *oldtup,
+						   *newtup;
+				Size		oldlen = 0;
+				Size		newlen = 0;
+
+				oldtup = change->data.tp.oldtuple;
+				newtup = change->data.tp.newtuple;
+
+				if (oldtup)
+				{
+					sz += sizeof(HeapTupleData);
+					oldlen = oldtup->tuple.t_len;
+					sz += oldlen;
+				}
+
+				if (newtup)
+				{
+					sz += sizeof(HeapTupleData);
+					newlen = newtup->tuple.t_len;
+					sz += newlen;
+				}
+
+				/* make sure we have enough space */
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+				/* might have been reallocated above */
+				ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+
+				if (oldlen)
+				{
+					memcpy(data, &oldtup->tuple, sizeof(HeapTupleData));
+					data += sizeof(HeapTupleData);
+
+					memcpy(data, oldtup->tuple.t_data, oldlen);
+					data += oldlen;
+				}
+
+				if (newlen)
+				{
+					memcpy(data, &newtup->tuple, sizeof(HeapTupleData));
+					data += sizeof(HeapTupleData);
+
+					memcpy(data, newtup->tuple.t_data, newlen);
+					data += newlen;
+				}
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				char	   *data;
+				Size		prefix_size = strlen(change->data.msg.prefix) + 1;
+
+				sz += prefix_size + change->data.msg.message_size +
+					sizeof(Size) + sizeof(Size);
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+
+				/* might have been reallocated above */
+				ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+
+				/* write the prefix including the size */
+				memcpy(data, &prefix_size, sizeof(Size));
+				data += sizeof(Size);
+				memcpy(data, change->data.msg.prefix,
+					   prefix_size);
+				data += prefix_size;
+
+				/* write the message including the size */
+				memcpy(data, &change->data.msg.message_size, sizeof(Size));
+				data += sizeof(Size);
+				memcpy(data, change->data.msg.message,
+					   change->data.msg.message_size);
+				data += change->data.msg.message_size;
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INVALIDATION:
+			{
+				char	   *data;
+				Size		inval_size = sizeof(SharedInvalidationMessage) *
+				change->data.inval.ninvalidations;
+
+				sz += inval_size;
+
+				ReorderBufferSerializeReserve(rb, sz);
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+
+				/* might have been reallocated above */
+				ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+				memcpy(data, change->data.inval.invalidations, inval_size);
+				data += inval_size;
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
+			{
+				Snapshot	snap;
+				char	   *data;
+
+				snap = change->data.snapshot;
+
+				sz += sizeof(SnapshotData) +
+					sizeof(TransactionId) * snap->xcnt +
+					sizeof(TransactionId) * snap->subxcnt;
+
+				/* make sure we have enough space */
+				ReorderBufferSerializeReserve(rb, sz);
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+				/* might have been reallocated above */
+				ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+
+				memcpy(data, snap, sizeof(SnapshotData));
+				data += sizeof(SnapshotData);
+
+				if (snap->xcnt)
+				{
+					memcpy(data, snap->xip,
+						   sizeof(TransactionId) * snap->xcnt);
+					data += sizeof(TransactionId) * snap->xcnt;
+				}
+
+				if (snap->subxcnt)
+				{
+					memcpy(data, snap->subxip,
+						   sizeof(TransactionId) * snap->subxcnt);
+					data += sizeof(TransactionId) * snap->subxcnt;
+				}
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_TRUNCATE:
+			{
+				Size		size;
+				char	   *data;
+
+				/* account for the OIDs of truncated relations */
+				size = sizeof(Oid) * change->data.truncate.nrelids;
+				sz += size;
+
+				/* make sure we have enough space */
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+				/* might have been reallocated above */
+				ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+
+				memcpy(data, change->data.truncate.relids, size);
+				data += size;
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
+		case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
+		case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
+			/* ReorderBufferChange contains everything important */
+			break;
+	}
+
+	ondisk->size = sz;
+
+	errno = 0;
+	pgstat_report_wait_start(WAIT_EVENT_REORDER_BUFFER_WRITE);
+	if (write(fd, rb->outbuf, ondisk->size) != ondisk->size)
+	{
+		int			save_errno = errno;
+
+		CloseTransientFile(fd);
+
+		/* if write didn't set errno, assume problem is no disk space */
+		errno = save_errno ? save_errno : ENOSPC;
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not write to data file for XID %u: %m",
+						txn->xid)));
+	}
+	pgstat_report_wait_end();
+
+	/*
+	 * Keep the transaction's final_lsn up to date with each change we send to
+	 * disk, so that ReorderBufferRestoreCleanup works correctly.  (We used to
+	 * only do this on commit and abort records, but that doesn't work if a
+	 * system crash leaves a transaction without its abort record).
+	 *
+	 * Make sure not to move it backwards.
+	 */
+	if (txn->final_lsn < change->lsn)
+		txn->final_lsn = change->lsn;
+
+	Assert(ondisk->change.action == change->action);
+}
+
+/* Returns true, if the output plugin supports streaming, false, otherwise. */
+static inline bool
+ReorderBufferCanStream(ReorderBuffer *rb)
+{
+	LogicalDecodingContext *ctx = rb->private_data;
+
+	return ctx->streaming;
+}
+
+/* Returns true, if the streaming can be started now, false, otherwise. */
+static inline bool
+ReorderBufferCanStartStreaming(ReorderBuffer *rb)
+{
+	LogicalDecodingContext *ctx = rb->private_data;
+	SnapBuild  *builder = ctx->snapshot_builder;
+
+	/* We can't start streaming unless a consistent state is reached. */
+	if (SnapBuildCurrentState(builder) < SNAPBUILD_CONSISTENT)
+		return false;
+
+	/*
+	 * We can't start streaming immediately even if the streaming is enabled
+	 * because we previously decoded this transaction and now just are
+	 * restarting.
+	 */
+	if (ReorderBufferCanStream(rb) &&
+		!SnapBuildXactNeedsSkip(builder, ctx->reader->EndRecPtr))
+		return true;
+
+	return false;
+}
+
+/*
+ * Send data of a large transaction (and its subtransactions) to the
+ * output plugin, but using the stream API.
+ */
+static void
+ReorderBufferStreamTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	Snapshot	snapshot_now;
+	CommandId	command_id;
+	Size		stream_bytes;
+	bool		txn_is_streamed;
+
+	/* We can never reach here for a subtransaction. */
+	Assert(txn->toptxn == NULL);
+
+	/*
+	 * We can't make any assumptions about base snapshot here, similar to what
+	 * ReorderBufferCommit() does. That relies on base_snapshot getting
+	 * transferred from subxact in ReorderBufferCommitChild(), but that was
+	 * not yet called as the transaction is in-progress.
+	 *
+	 * So just walk the subxacts and use the same logic here. But we only need
+	 * to do that once, when the transaction is streamed for the first time.
+	 * After that we need to reuse the snapshot from the previous run.
+	 *
+	 * Unlike DecodeCommit which adds xids of all the subtransactions in
+	 * snapshot's xip array via SnapBuildCommittedTxn, we can't do that here
+	 * but we do add them to subxip array instead via ReorderBufferCopySnap.
+	 * This allows the catalog changes made in subtransactions decoded till
+	 * now to be visible.
+	 */
+	if (txn->snapshot_now == NULL)
+	{
+		dlist_iter	subxact_i;
+
+		/* make sure this transaction is streamed for the first time */
+		Assert(!rbtxn_is_streamed(txn));
+
+		/* at the beginning we should have invalid command ID */
+		Assert(txn->command_id == InvalidCommandId);
+
+		dlist_foreach(subxact_i, &txn->subtxns)
+		{
+			ReorderBufferTXN *subtxn;
+
+			subtxn = dlist_container(ReorderBufferTXN, node, subxact_i.cur);
+			ReorderBufferTransferSnapToParent(txn, subtxn);
+		}
+
+		/*
+		 * If this transaction has no snapshot, it didn't make any changes to
+		 * the database till now, so there's nothing to decode.
+		 */
+		if (txn->base_snapshot == NULL)
+		{
+			Assert(txn->ninvalidations == 0);
+			return;
+		}
+
+		command_id = FirstCommandId;
+		snapshot_now = ReorderBufferCopySnap(rb, txn->base_snapshot,
+											 txn, command_id);
+	}
+	else
+	{
+		/* the transaction must have been already streamed */
+		Assert(rbtxn_is_streamed(txn));
+
+		/*
+		 * Nah, we already have snapshot from the previous streaming run. We
+		 * assume new subxacts can't move the LSN backwards, and so can't beat
+		 * the LSN condition in the previous branch (so no need to walk
+		 * through subxacts again). In fact, we must not do that as we may be
+		 * using snapshot half-way through the subxact.
+		 */
+		command_id = txn->command_id;
+
+		/*
+		 * We can't use txn->snapshot_now directly because after the last
+		 * streaming run, we might have got some new sub-transactions. So we
+		 * need to add them to the snapshot.
+		 */
+		snapshot_now = ReorderBufferCopySnap(rb, txn->snapshot_now,
+											 txn, command_id);
+
+		/* Free the previously copied snapshot. */
+		Assert(txn->snapshot_now->copied);
+		ReorderBufferFreeSnap(rb, txn->snapshot_now);
+		txn->snapshot_now = NULL;
+	}
+
+	/*
+	 * Remember this information to be used later to update stats. We can't
+	 * update the stats here as an error while processing the changes would
+	 * lead to the accumulation of stats even though we haven't streamed all
+	 * the changes.
+	 */
+	txn_is_streamed = rbtxn_is_streamed(txn);
+	stream_bytes = txn->total_size;
+
+	/* Process and send the changes to output plugin. */
+	ReorderBufferProcessTXN(rb, txn, InvalidXLogRecPtr, snapshot_now,
+							command_id, true);
+
+	rb->streamCount += 1;
+	rb->streamBytes += stream_bytes;
+
+	/* Don't consider already streamed transaction. */
+	rb->streamTxns += (txn_is_streamed) ? 0 : 1;
+
+	/* update the decoding stats */
+	UpdateDecodingStats((LogicalDecodingContext *) rb->private_data);
+
+	Assert(dlist_is_empty(&txn->changes));
+	Assert(txn->nentries == 0);
+	Assert(txn->nentries_mem == 0);
+}
+
+/*
+ * Size of a change in memory.
+ */
+static Size
+ReorderBufferChangeSize(ReorderBufferChange *change)
+{
+	Size		sz = sizeof(ReorderBufferChange);
+
+	switch (change->action)
+	{
+			/* fall through these, they're all similar enough */
+		case REORDER_BUFFER_CHANGE_INSERT:
+		case REORDER_BUFFER_CHANGE_UPDATE:
+		case REORDER_BUFFER_CHANGE_DELETE:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
+			{
+				ReorderBufferTupleBuf *oldtup,
+						   *newtup;
+				Size		oldlen = 0;
+				Size		newlen = 0;
+
+				oldtup = change->data.tp.oldtuple;
+				newtup = change->data.tp.newtuple;
+
+				if (oldtup)
+				{
+					sz += sizeof(HeapTupleData);
+					oldlen = oldtup->tuple.t_len;
+					sz += oldlen;
+				}
+
+				if (newtup)
+				{
+					sz += sizeof(HeapTupleData);
+					newlen = newtup->tuple.t_len;
+					sz += newlen;
+				}
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				Size		prefix_size = strlen(change->data.msg.prefix) + 1;
+
+				sz += prefix_size + change->data.msg.message_size +
+					sizeof(Size) + sizeof(Size);
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INVALIDATION:
+			{
+				sz += sizeof(SharedInvalidationMessage) *
+					change->data.inval.ninvalidations;
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
+			{
+				Snapshot	snap;
+
+				snap = change->data.snapshot;
+
+				sz += sizeof(SnapshotData) +
+					sizeof(TransactionId) * snap->xcnt +
+					sizeof(TransactionId) * snap->subxcnt;
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_TRUNCATE:
+			{
+				sz += sizeof(Oid) * change->data.truncate.nrelids;
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
+		case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
+		case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
+			/* ReorderBufferChange contains everything important */
+			break;
+	}
+
+	return sz;
+}
+
+
+/*
+ * Restore a number of changes spilled to disk back into memory.
+ */
+static Size
+ReorderBufferRestoreChanges(ReorderBuffer *rb, ReorderBufferTXN *txn,
+							TXNEntryFile *file, XLogSegNo *segno)
+{
+	Size		restored = 0;
+	XLogSegNo	last_segno;
+	dlist_mutable_iter cleanup_iter;
+	File	   *fd = &file->vfd;
+
+	Assert(txn->first_lsn != InvalidXLogRecPtr);
+	Assert(txn->final_lsn != InvalidXLogRecPtr);
+
+	/* free current entries, so we have memory for more */
+	dlist_foreach_modify(cleanup_iter, &txn->changes)
+	{
+		ReorderBufferChange *cleanup =
+		dlist_container(ReorderBufferChange, node, cleanup_iter.cur);
+
+		dlist_delete(&cleanup->node);
+		ReorderBufferReturnChange(rb, cleanup, true);
+	}
+	txn->nentries_mem = 0;
+	Assert(dlist_is_empty(&txn->changes));
+
+	XLByteToSeg(txn->final_lsn, last_segno, wal_segment_size);
+
+	while (restored < max_changes_in_memory && *segno <= last_segno)
+	{
+		int			readBytes;
+		ReorderBufferDiskChange *ondisk;
+
+		if (*fd == -1)
+		{
+			char		path[MAXPGPATH];
+
+			/* first time in */
+			if (*segno == 0)
+				XLByteToSeg(txn->first_lsn, *segno, wal_segment_size);
+
+			Assert(*segno != 0 || dlist_is_empty(&txn->changes));
+
+			/*
+			 * No need to care about TLIs here, only used during a single run,
+			 * so each LSN only maps to a specific WAL record.
+			 */
+			ReorderBufferSerializedPath(path, MyReplicationSlot, txn->xid,
+										*segno);
+
+			*fd = PathNameOpenFile(path, O_RDONLY | PG_BINARY);
+
+			/* No harm in resetting the offset even in case of failure */
+			file->curOffset = 0;
+
+			if (*fd < 0 && errno == ENOENT)
+			{
+				*fd = -1;
+				(*segno)++;
+				continue;
+			}
+			else if (*fd < 0)
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not open file \"%s\": %m",
+								path)));
+		}
+
+		/*
+		 * Read the statically sized part of a change which has information
+		 * about the total size. If we couldn't read a record, we're at the
+		 * end of this file.
+		 */
+		ReorderBufferSerializeReserve(rb, sizeof(ReorderBufferDiskChange));
+		readBytes = FileRead(file->vfd, rb->outbuf,
+							 sizeof(ReorderBufferDiskChange),
+							 file->curOffset, WAIT_EVENT_REORDER_BUFFER_READ);
+
+		/* eof */
+		if (readBytes == 0)
+		{
+			FileClose(*fd);
+			*fd = -1;
+			(*segno)++;
+			continue;
+		}
+		else if (readBytes < 0)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read from reorderbuffer spill file: %m")));
+		else if (readBytes != sizeof(ReorderBufferDiskChange))
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read from reorderbuffer spill file: read %d instead of %u bytes",
+							readBytes,
+							(uint32) sizeof(ReorderBufferDiskChange))));
+
+		file->curOffset += readBytes;
+
+		ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+
+		ReorderBufferSerializeReserve(rb,
+									  sizeof(ReorderBufferDiskChange) + ondisk->size);
+		ondisk = (ReorderBufferDiskChange *) rb->outbuf;
+
+		readBytes = FileRead(file->vfd,
+							 rb->outbuf + sizeof(ReorderBufferDiskChange),
+							 ondisk->size - sizeof(ReorderBufferDiskChange),
+							 file->curOffset,
+							 WAIT_EVENT_REORDER_BUFFER_READ);
+
+		if (readBytes < 0)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read from reorderbuffer spill file: %m")));
+		else if (readBytes != ondisk->size - sizeof(ReorderBufferDiskChange))
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read from reorderbuffer spill file: read %d instead of %u bytes",
+							readBytes,
+							(uint32) (ondisk->size - sizeof(ReorderBufferDiskChange)))));
+
+		file->curOffset += readBytes;
+
+		/*
+		 * ok, read a full change from disk, now restore it into proper
+		 * in-memory format
+		 */
+		ReorderBufferRestoreChange(rb, txn, rb->outbuf);
+		restored++;
+	}
+
+	return restored;
+}
+
+/*
+ * Convert change from its on-disk format to in-memory format and queue it onto
+ * the TXN's ->changes list.
+ *
+ * Note: although "data" is declared char*, at entry it points to a
+ * maxalign'd buffer, making it safe in most of this function to assume
+ * that the pointed-to data is suitably aligned for direct access.
+ */
+static void
+ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
+						   char *data)
+{
+	ReorderBufferDiskChange *ondisk;
+	ReorderBufferChange *change;
+
+	ondisk = (ReorderBufferDiskChange *) data;
+
+	change = ReorderBufferGetChange(rb);
+
+	/* copy static part */
+	memcpy(change, &ondisk->change, sizeof(ReorderBufferChange));
+
+	data += sizeof(ReorderBufferDiskChange);
+
+	/* restore individual stuff */
+	switch (change->action)
+	{
+			/* fall through these, they're all similar enough */
+		case REORDER_BUFFER_CHANGE_INSERT:
+		case REORDER_BUFFER_CHANGE_UPDATE:
+		case REORDER_BUFFER_CHANGE_DELETE:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
+			if (change->data.tp.oldtuple)
+			{
+				uint32		tuplelen = ((HeapTuple) data)->t_len;
+
+				change->data.tp.oldtuple =
+					ReorderBufferGetTupleBuf(rb, tuplelen - SizeofHeapTupleHeader);
+
+				/* restore ->tuple */
+				memcpy(&change->data.tp.oldtuple->tuple, data,
+					   sizeof(HeapTupleData));
+				data += sizeof(HeapTupleData);
+
+				/* reset t_data pointer into the new tuplebuf */
+				change->data.tp.oldtuple->tuple.t_data =
+					ReorderBufferTupleBufData(change->data.tp.oldtuple);
+
+				/* restore tuple data itself */
+				memcpy(change->data.tp.oldtuple->tuple.t_data, data, tuplelen);
+				data += tuplelen;
+			}
+
+			if (change->data.tp.newtuple)
+			{
+				/* here, data might not be suitably aligned! */
+				uint32		tuplelen;
+
+				memcpy(&tuplelen, data + offsetof(HeapTupleData, t_len),
+					   sizeof(uint32));
+
+				change->data.tp.newtuple =
+					ReorderBufferGetTupleBuf(rb, tuplelen - SizeofHeapTupleHeader);
+
+				/* restore ->tuple */
+				memcpy(&change->data.tp.newtuple->tuple, data,
+					   sizeof(HeapTupleData));
+				data += sizeof(HeapTupleData);
+
+				/* reset t_data pointer into the new tuplebuf */
+				change->data.tp.newtuple->tuple.t_data =
+					ReorderBufferTupleBufData(change->data.tp.newtuple);
+
+				/* restore tuple data itself */
+				memcpy(change->data.tp.newtuple->tuple.t_data, data, tuplelen);
+				data += tuplelen;
+			}
+
+			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				Size		prefix_size;
+
+				/* read prefix */
+				memcpy(&prefix_size, data, sizeof(Size));
+				data += sizeof(Size);
+				change->data.msg.prefix = MemoryContextAlloc(rb->context,
+															 prefix_size);
+				memcpy(change->data.msg.prefix, data, prefix_size);
+				Assert(change->data.msg.prefix[prefix_size - 1] == '\0');
+				data += prefix_size;
+
+				/* read the message */
+				memcpy(&change->data.msg.message_size, data, sizeof(Size));
+				data += sizeof(Size);
+				change->data.msg.message = MemoryContextAlloc(rb->context,
+															  change->data.msg.message_size);
+				memcpy(change->data.msg.message, data,
+					   change->data.msg.message_size);
+				data += change->data.msg.message_size;
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INVALIDATION:
+			{
+				Size		inval_size = sizeof(SharedInvalidationMessage) *
+				change->data.inval.ninvalidations;
+
+				change->data.inval.invalidations =
+					MemoryContextAlloc(rb->context, inval_size);
+
+				/* read the message */
+				memcpy(change->data.inval.invalidations, data, inval_size);
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
+			{
+				Snapshot	oldsnap;
+				Snapshot	newsnap;
+				Size		size;
+
+				oldsnap = (Snapshot) data;
+
+				size = sizeof(SnapshotData) +
+					sizeof(TransactionId) * oldsnap->xcnt +
+					sizeof(TransactionId) * (oldsnap->subxcnt + 0);
+
+				change->data.snapshot = MemoryContextAllocZero(rb->context, size);
+
+				newsnap = change->data.snapshot;
+
+				memcpy(newsnap, data, size);
+				newsnap->xip = (TransactionId *)
+					(((char *) newsnap) + sizeof(SnapshotData));
+				newsnap->subxip = newsnap->xip + newsnap->xcnt;
+				newsnap->copied = true;
+				break;
+			}
+			/* the base struct contains all the data, easy peasy */
+		case REORDER_BUFFER_CHANGE_TRUNCATE:
+			{
+				Oid		   *relids;
+
+				relids = ReorderBufferGetRelids(rb,
+												change->data.truncate.nrelids);
+				memcpy(relids, data, change->data.truncate.nrelids * sizeof(Oid));
+				change->data.truncate.relids = relids;
+
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM:
+		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT:
+		case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
+		case REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID:
+			break;
+	}
+
+	dlist_push_tail(&txn->changes, &change->node);
+	txn->nentries_mem++;
+
+	/*
+	 * Update memory accounting for the restored change.  We need to do this
+	 * although we don't check the memory limit when restoring the changes in
+	 * this branch (we only do that when initially queueing the changes after
+	 * decoding), because we will release the changes later, and that will
+	 * update the accounting too (subtracting the size from the counters). And
+	 * we don't want to underflow there.
+	 */
+	ReorderBufferChangeMemoryUpdate(rb, change, true,
+									ReorderBufferChangeSize(change));
+}
+
+/*
+ * Remove all on-disk stored for the passed in transaction.
+ */
+static void
+ReorderBufferRestoreCleanup(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	XLogSegNo	first;
+	XLogSegNo	cur;
+	XLogSegNo	last;
+
+	Assert(txn->first_lsn != InvalidXLogRecPtr);
+	Assert(txn->final_lsn != InvalidXLogRecPtr);
+
+	XLByteToSeg(txn->first_lsn, first, wal_segment_size);
+	XLByteToSeg(txn->final_lsn, last, wal_segment_size);
+
+	/* iterate over all possible filenames, and delete them */
+	for (cur = first; cur <= last; cur++)
+	{
+		char		path[MAXPGPATH];
+
+		ReorderBufferSerializedPath(path, MyReplicationSlot, txn->xid, cur);
+		if (unlink(path) != 0 && errno != ENOENT)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not remove file \"%s\": %m", path)));
+	}
+}
+
+/*
+ * Remove any leftover serialized reorder buffers from a slot directory after a
+ * prior crash or decoding session exit.
+ */
+static void
+ReorderBufferCleanupSerializedTXNs(const char *slotname)
+{
+	DIR		   *spill_dir;
+	struct dirent *spill_de;
+	struct stat statbuf;
+	char		path[MAXPGPATH * 2 + 12];
+
+	sprintf(path, "pg_replslot/%s", slotname);
+
+	/* we're only handling directories here, skip if it's not ours */
+	if (lstat(path, &statbuf) == 0 && !S_ISDIR(statbuf.st_mode))
+		return;
+
+	spill_dir = AllocateDir(path);
+	while ((spill_de = ReadDirExtended(spill_dir, path, INFO)) != NULL)
+	{
+		/* only look at names that can be ours */
+		if (strncmp(spill_de->d_name, "xid", 3) == 0)
+		{
+			snprintf(path, sizeof(path),
+					 "pg_replslot/%s/%s", slotname,
+					 spill_de->d_name);
+
+			if (unlink(path) != 0)
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not remove file \"%s\" during removal of pg_replslot/%s/xid*: %m",
+								path, slotname)));
+		}
+	}
+	FreeDir(spill_dir);
+}
+
+/*
+ * Given a replication slot, transaction ID and segment number, fill in the
+ * corresponding spill file into 'path', which is a caller-owned buffer of size
+ * at least MAXPGPATH.
+ */
+static void
+ReorderBufferSerializedPath(char *path, ReplicationSlot *slot, TransactionId xid,
+							XLogSegNo segno)
+{
+	XLogRecPtr	recptr;
+
+	XLogSegNoOffsetToRecPtr(segno, 0, wal_segment_size, recptr);
+
+	snprintf(path, MAXPGPATH, "pg_replslot/%s/xid-%u-lsn-%X-%X.spill",
+			 NameStr(MyReplicationSlot->data.name),
+			 xid, LSN_FORMAT_ARGS(recptr));
+}
+
+/*
+ * Delete all data spilled to disk after we've restarted/crashed. It will be
+ * recreated when the respective slots are reused.
+ */
+void
+StartupReorderBuffer(void)
+{
+	DIR		   *logical_dir;
+	struct dirent *logical_de;
+
+	logical_dir = AllocateDir("pg_replslot");
+	while ((logical_de = ReadDir(logical_dir, "pg_replslot")) != NULL)
+	{
+		if (strcmp(logical_de->d_name, ".") == 0 ||
+			strcmp(logical_de->d_name, "..") == 0)
+			continue;
+
+		/* if it cannot be a slot, skip the directory */
+		if (!ReplicationSlotValidateName(logical_de->d_name, DEBUG2))
+			continue;
+
+		/*
+		 * ok, has to be a surviving logical slot, iterate and delete
+		 * everything starting with xid-*
+		 */
+		ReorderBufferCleanupSerializedTXNs(logical_de->d_name);
+	}
+	FreeDir(logical_dir);
+}
+
+/* ---------------------------------------
+ * toast reassembly support
+ * ---------------------------------------
+ */
+
+/*
+ * Initialize per tuple toast reconstruction support.
+ */
+static void
+ReorderBufferToastInitHash(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	HASHCTL		hash_ctl;
+
+	Assert(txn->toast_hash == NULL);
+
+	hash_ctl.keysize = sizeof(Oid);
+	hash_ctl.entrysize = sizeof(ReorderBufferToastEnt);
+	hash_ctl.hcxt = rb->context;
+	txn->toast_hash = hash_create("ReorderBufferToastHash", 5, &hash_ctl,
+								  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+}
+
+/*
+ * Per toast-chunk handling for toast reconstruction
+ *
+ * Appends a toast chunk so we can reconstruct it when the tuple "owning" the
+ * toasted Datum comes along.
+ */
+static void
+ReorderBufferToastAppendChunk(ReorderBuffer *rb, ReorderBufferTXN *txn,
+							  Relation relation, ReorderBufferChange *change)
+{
+	ReorderBufferToastEnt *ent;
+	ReorderBufferTupleBuf *newtup;
+	bool		found;
+	int32		chunksize;
+	bool		isnull;
+	Pointer		chunk;
+	TupleDesc	desc = RelationGetDescr(relation);
+	Oid			chunk_id;
+	int32		chunk_seq;
+
+	if (txn->toast_hash == NULL)
+		ReorderBufferToastInitHash(rb, txn);
+
+	Assert(IsToastRelation(relation));
+
+	newtup = change->data.tp.newtuple;
+	chunk_id = DatumGetObjectId(fastgetattr(&newtup->tuple, 1, desc, &isnull));
+	Assert(!isnull);
+	chunk_seq = DatumGetInt32(fastgetattr(&newtup->tuple, 2, desc, &isnull));
+	Assert(!isnull);
+
+	ent = (ReorderBufferToastEnt *)
+		hash_search(txn->toast_hash,
+					(void *) &chunk_id,
+					HASH_ENTER,
+					&found);
+
+	if (!found)
+	{
+		Assert(ent->chunk_id == chunk_id);
+		ent->num_chunks = 0;
+		ent->last_chunk_seq = 0;
+		ent->size = 0;
+		ent->reconstructed = NULL;
+		dlist_init(&ent->chunks);
+
+		if (chunk_seq != 0)
+			elog(ERROR, "got sequence entry %d for toast chunk %u instead of seq 0",
+				 chunk_seq, chunk_id);
+	}
+	else if (found && chunk_seq != ent->last_chunk_seq + 1)
+		elog(ERROR, "got sequence entry %d for toast chunk %u instead of seq %d",
+			 chunk_seq, chunk_id, ent->last_chunk_seq + 1);
+
+	chunk = DatumGetPointer(fastgetattr(&newtup->tuple, 3, desc, &isnull));
+	Assert(!isnull);
+
+	/* calculate size so we can allocate the right size at once later */
+	if (!VARATT_IS_EXTENDED(chunk))
+		chunksize = VARSIZE(chunk) - VARHDRSZ;
+	else if (VARATT_IS_SHORT(chunk))
+		/* could happen due to heap_form_tuple doing its thing */
+		chunksize = VARSIZE_SHORT(chunk) - VARHDRSZ_SHORT;
+	else
+		elog(ERROR, "unexpected type of toast chunk");
+
+	ent->size += chunksize;
+	ent->last_chunk_seq = chunk_seq;
+	ent->num_chunks++;
+	dlist_push_tail(&ent->chunks, &change->node);
+}
+
+/*
+ * Rejigger change->newtuple to point to in-memory toast tuples instead to
+ * on-disk toast tuples that may not longer exist (think DROP TABLE or VACUUM).
+ *
+ * We cannot replace unchanged toast tuples though, so those will still point
+ * to on-disk toast data.
+ *
+ * While updating the existing change with detoasted tuple data, we need to
+ * update the memory accounting info, because the change size will differ.
+ * Otherwise the accounting may get out of sync, triggering serialization
+ * at unexpected times.
+ *
+ * We simply subtract size of the change before rejiggering the tuple, and
+ * then adding the new size. This makes it look like the change was removed
+ * and then added back, except it only tweaks the accounting info.
+ *
+ * In particular it can't trigger serialization, which would be pointless
+ * anyway as it happens during commit processing right before handing
+ * the change to the output plugin.
+ */
+static void
+ReorderBufferToastReplace(ReorderBuffer *rb, ReorderBufferTXN *txn,
+						  Relation relation, ReorderBufferChange *change)
+{
+	TupleDesc	desc;
+	int			natt;
+	Datum	   *attrs;
+	bool	   *isnull;
+	bool	   *free;
+	HeapTuple	tmphtup;
+	Relation	toast_rel;
+	TupleDesc	toast_desc;
+	MemoryContext oldcontext;
+	ReorderBufferTupleBuf *newtup;
+	Size		old_size;
+
+	/* no toast tuples changed */
+	if (txn->toast_hash == NULL)
+		return;
+
+	/*
+	 * We're going to modify the size of the change. So, to make sure the
+	 * accounting is correct we record the current change size and then after
+	 * re-computing the change we'll subtract the recorded size and then
+	 * re-add the new change size at the end. We don't immediately subtract
+	 * the old size because if there is any error before we add the new size,
+	 * we will release the changes and that will update the accounting info
+	 * (subtracting the size from the counters). And we don't want to
+	 * underflow there.
+	 */
+	old_size = ReorderBufferChangeSize(change);
+
+	oldcontext = MemoryContextSwitchTo(rb->context);
+
+	/* we should only have toast tuples in an INSERT or UPDATE */
+	Assert(change->data.tp.newtuple);
+
+	desc = RelationGetDescr(relation);
+
+	toast_rel = RelationIdGetRelation(relation->rd_rel->reltoastrelid);
+	if (!RelationIsValid(toast_rel))
+		elog(ERROR, "could not open toast relation with OID %u (base relation \"%s\")",
+			 relation->rd_rel->reltoastrelid, RelationGetRelationName(relation));
+
+	toast_desc = RelationGetDescr(toast_rel);
+
+	/* should we allocate from stack instead? */
+	attrs = palloc0(sizeof(Datum) * desc->natts);
+	isnull = palloc0(sizeof(bool) * desc->natts);
+	free = palloc0(sizeof(bool) * desc->natts);
+
+	newtup = change->data.tp.newtuple;
+
+	heap_deform_tuple(&newtup->tuple, desc, attrs, isnull);
+
+	for (natt = 0; natt < desc->natts; natt++)
+	{
+		Form_pg_attribute attr = TupleDescAttr(desc, natt);
+		ReorderBufferToastEnt *ent;
+		struct varlena *varlena;
+
+		/* va_rawsize is the size of the original datum -- including header */
+		struct varatt_external toast_pointer;
+		struct varatt_indirect redirect_pointer;
+		struct varlena *new_datum = NULL;
+		struct varlena *reconstructed;
+		dlist_iter	it;
+		Size		data_done = 0;
+
+		/* system columns aren't toasted */
+		if (attr->attnum < 0)
+			continue;
+
+		if (attr->attisdropped)
+			continue;
+
+		/* not a varlena datatype */
+		if (attr->attlen != -1)
+			continue;
+
+		/* no data */
+		if (isnull[natt])
+			continue;
+
+		/* ok, we know we have a toast datum */
+		varlena = (struct varlena *) DatumGetPointer(attrs[natt]);
+
+		/* no need to do anything if the tuple isn't external */
+		if (!VARATT_IS_EXTERNAL(varlena))
+			continue;
+
+		VARATT_EXTERNAL_GET_POINTER(toast_pointer, varlena);
+
+		/*
+		 * Check whether the toast tuple changed, replace if so.
+		 */
+		ent = (ReorderBufferToastEnt *)
+			hash_search(txn->toast_hash,
+						(void *) &toast_pointer.va_valueid,
+						HASH_FIND,
+						NULL);
+		if (ent == NULL)
+			continue;
+
+		new_datum =
+			(struct varlena *) palloc0(INDIRECT_POINTER_SIZE);
+
+		free[natt] = true;
+
+		reconstructed = palloc0(toast_pointer.va_rawsize);
+
+		ent->reconstructed = reconstructed;
+
+		/* stitch toast tuple back together from its parts */
+		dlist_foreach(it, &ent->chunks)
+		{
+			bool		isnull;
+			ReorderBufferChange *cchange;
+			ReorderBufferTupleBuf *ctup;
+			Pointer		chunk;
+
+			cchange = dlist_container(ReorderBufferChange, node, it.cur);
+			ctup = cchange->data.tp.newtuple;
+			chunk = DatumGetPointer(fastgetattr(&ctup->tuple, 3, toast_desc, &isnull));
+
+			Assert(!isnull);
+			Assert(!VARATT_IS_EXTERNAL(chunk));
+			Assert(!VARATT_IS_SHORT(chunk));
+
+			memcpy(VARDATA(reconstructed) + data_done,
+				   VARDATA(chunk),
+				   VARSIZE(chunk) - VARHDRSZ);
+			data_done += VARSIZE(chunk) - VARHDRSZ;
+		}
+		Assert(data_done == VARATT_EXTERNAL_GET_EXTSIZE(toast_pointer));
+
+		/* make sure its marked as compressed or not */
+		if (VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer))
+			SET_VARSIZE_COMPRESSED(reconstructed, data_done + VARHDRSZ);
+		else
+			SET_VARSIZE(reconstructed, data_done + VARHDRSZ);
+
+		memset(&redirect_pointer, 0, sizeof(redirect_pointer));
+		redirect_pointer.pointer = reconstructed;
+
+		SET_VARTAG_EXTERNAL(new_datum, VARTAG_INDIRECT);
+		memcpy(VARDATA_EXTERNAL(new_datum), &redirect_pointer,
+			   sizeof(redirect_pointer));
+
+		attrs[natt] = PointerGetDatum(new_datum);
+	}
+
+	/*
+	 * Build tuple in separate memory & copy tuple back into the tuplebuf
+	 * passed to the output plugin. We can't directly heap_fill_tuple() into
+	 * the tuplebuf because attrs[] will point back into the current content.
+	 */
+	tmphtup = heap_form_tuple(desc, attrs, isnull);
+	Assert(newtup->tuple.t_len <= MaxHeapTupleSize);
+	Assert(ReorderBufferTupleBufData(newtup) == newtup->tuple.t_data);
+
+	memcpy(newtup->tuple.t_data, tmphtup->t_data, tmphtup->t_len);
+	newtup->tuple.t_len = tmphtup->t_len;
+
+	/*
+	 * free resources we won't further need, more persistent stuff will be
+	 * free'd in ReorderBufferToastReset().
+	 */
+	RelationClose(toast_rel);
+	pfree(tmphtup);
+	for (natt = 0; natt < desc->natts; natt++)
+	{
+		if (free[natt])
+			pfree(DatumGetPointer(attrs[natt]));
+	}
+	pfree(attrs);
+	pfree(free);
+	pfree(isnull);
+
+	MemoryContextSwitchTo(oldcontext);
+
+	/* subtract the old change size */
+	ReorderBufferChangeMemoryUpdate(rb, change, false, old_size);
+	/* now add the change back, with the correct size */
+	ReorderBufferChangeMemoryUpdate(rb, change, true,
+									ReorderBufferChangeSize(change));
+}
+
+/*
+ * Free all resources allocated for toast reconstruction.
+ */
+static void
+ReorderBufferToastReset(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+	HASH_SEQ_STATUS hstat;
+	ReorderBufferToastEnt *ent;
+
+	if (txn->toast_hash == NULL)
+		return;
+
+	/* sequentially walk over the hash and free everything */
+	hash_seq_init(&hstat, txn->toast_hash);
+	while ((ent = (ReorderBufferToastEnt *) hash_seq_search(&hstat)) != NULL)
+	{
+		dlist_mutable_iter it;
+
+		if (ent->reconstructed != NULL)
+			pfree(ent->reconstructed);
+
+		dlist_foreach_modify(it, &ent->chunks)
+		{
+			ReorderBufferChange *change =
+			dlist_container(ReorderBufferChange, node, it.cur);
+
+			dlist_delete(&change->node);
+			ReorderBufferReturnChange(rb, change, true);
+		}
+	}
+
+	hash_destroy(txn->toast_hash);
+	txn->toast_hash = NULL;
+}
+
+
+/* ---------------------------------------
+ * Visibility support for logical decoding
+ *
+ *
+ * Lookup actual cmin/cmax values when using decoding snapshot. We can't
+ * always rely on stored cmin/cmax values because of two scenarios:
+ *
+ * * A tuple got changed multiple times during a single transaction and thus
+ *	 has got a combo CID. Combo CIDs are only valid for the duration of a
+ *	 single transaction.
+ * * A tuple with a cmin but no cmax (and thus no combo CID) got
+ *	 deleted/updated in another transaction than the one which created it
+ *	 which we are looking at right now. As only one of cmin, cmax or combo CID
+ *	 is actually stored in the heap we don't have access to the value we
+ *	 need anymore.
+ *
+ * To resolve those problems we have a per-transaction hash of (cmin,
+ * cmax) tuples keyed by (relfilenode, ctid) which contains the actual
+ * (cmin, cmax) values. That also takes care of combo CIDs by simply
+ * not caring about them at all. As we have the real cmin/cmax values
+ * combo CIDs aren't interesting.
+ *
+ * As we only care about catalog tuples here the overhead of this
+ * hashtable should be acceptable.
+ *
+ * Heap rewrites complicate this a bit, check rewriteheap.c for
+ * details.
+ * -------------------------------------------------------------------------
+ */
+
+/* struct for sorting mapping files by LSN efficiently */
+typedef struct RewriteMappingFile
+{
+	XLogRecPtr	lsn;
+	char		fname[MAXPGPATH];
+} RewriteMappingFile;
+
+#ifdef NOT_USED
+static void
+DisplayMapping(HTAB *tuplecid_data)
+{
+	HASH_SEQ_STATUS hstat;
+	ReorderBufferTupleCidEnt *ent;
+
+	hash_seq_init(&hstat, tuplecid_data);
+	while ((ent = (ReorderBufferTupleCidEnt *) hash_seq_search(&hstat)) != NULL)
+	{
+		elog(DEBUG3, "mapping: node: %u/%u/%u tid: %u/%u cmin: %u, cmax: %u",
+			 ent->key.relnode.dbNode,
+			 ent->key.relnode.spcNode,
+			 ent->key.relnode.relNode,
+			 ItemPointerGetBlockNumber(&ent->key.tid),
+			 ItemPointerGetOffsetNumber(&ent->key.tid),
+			 ent->cmin,
+			 ent->cmax
+			);
+	}
+}
+#endif
+
+/*
+ * Apply a single mapping file to tuplecid_data.
+ *
+ * The mapping file has to have been verified to be a) committed b) for our
+ * transaction c) applied in LSN order.
+ */
+static void
+ApplyLogicalMappingFile(HTAB *tuplecid_data, Oid relid, const char *fname)
+{
+	char		path[MAXPGPATH];
+	int			fd;
+	int			readBytes;
+	LogicalRewriteMappingData map;
+
+	sprintf(path, "pg_logical/mappings/%s", fname);
+	fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
+	if (fd < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not open file \"%s\": %m", path)));
+
+	while (true)
+	{
+		ReorderBufferTupleCidKey key;
+		ReorderBufferTupleCidEnt *ent;
+		ReorderBufferTupleCidEnt *new_ent;
+		bool		found;
+
+		/* be careful about padding */
+		memset(&key, 0, sizeof(ReorderBufferTupleCidKey));
+
+		/* read all mappings till the end of the file */
+		pgstat_report_wait_start(WAIT_EVENT_REORDER_LOGICAL_MAPPING_READ);
+		readBytes = read(fd, &map, sizeof(LogicalRewriteMappingData));
+		pgstat_report_wait_end();
+
+		if (readBytes < 0)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m",
+							path)));
+		else if (readBytes == 0)	/* EOF */
+			break;
+		else if (readBytes != sizeof(LogicalRewriteMappingData))
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read from file \"%s\": read %d instead of %d bytes",
+							path, readBytes,
+							(int32) sizeof(LogicalRewriteMappingData))));
+
+		key.relnode = map.old_node;
+		ItemPointerCopy(&map.old_tid,
+						&key.tid);
+
+
+		ent = (ReorderBufferTupleCidEnt *)
+			hash_search(tuplecid_data,
+						(void *) &key,
+						HASH_FIND,
+						NULL);
+
+		/* no existing mapping, no need to update */
+		if (!ent)
+			continue;
+
+		key.relnode = map.new_node;
+		ItemPointerCopy(&map.new_tid,
+						&key.tid);
+
+		new_ent = (ReorderBufferTupleCidEnt *)
+			hash_search(tuplecid_data,
+						(void *) &key,
+						HASH_ENTER,
+						&found);
+
+		if (found)
+		{
+			/*
+			 * Make sure the existing mapping makes sense. We sometime update
+			 * old records that did not yet have a cmax (e.g. pg_class' own
+			 * entry while rewriting it) during rewrites, so allow that.
+			 */
+			Assert(ent->cmin == InvalidCommandId || ent->cmin == new_ent->cmin);
+			Assert(ent->cmax == InvalidCommandId || ent->cmax == new_ent->cmax);
+		}
+		else
+		{
+			/* update mapping */
+			new_ent->cmin = ent->cmin;
+			new_ent->cmax = ent->cmax;
+			new_ent->combocid = ent->combocid;
+		}
+	}
+
+	if (CloseTransientFile(fd) != 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m", path)));
+}
+
+
+/*
+ * Check whether the TransactionId 'xid' is in the pre-sorted array 'xip'.
+ */
+static bool
+TransactionIdInArray(TransactionId xid, TransactionId *xip, Size num)
+{
+	return bsearch(&xid, xip, num,
+				   sizeof(TransactionId), xidComparator) != NULL;
+}
+
+/*
+ * list_sort() comparator for sorting RewriteMappingFiles in LSN order.
+ */
+static int
+file_sort_by_lsn(const ListCell *a_p, const ListCell *b_p)
+{
+	RewriteMappingFile *a = (RewriteMappingFile *) lfirst(a_p);
+	RewriteMappingFile *b = (RewriteMappingFile *) lfirst(b_p);
+
+	if (a->lsn < b->lsn)
+		return -1;
+	else if (a->lsn > b->lsn)
+		return 1;
+	return 0;
+}
+
+/*
+ * Apply any existing logical remapping files if there are any targeted at our
+ * transaction for relid.
+ */
+static void
+UpdateLogicalMappings(HTAB *tuplecid_data, Oid relid, Snapshot snapshot)
+{
+	DIR		   *mapping_dir;
+	struct dirent *mapping_de;
+	List	   *files = NIL;
+	ListCell   *file;
+	Oid			dboid = IsSharedRelation(relid) ? InvalidOid : MyDatabaseId;
+
+	mapping_dir = AllocateDir("pg_logical/mappings");
+	while ((mapping_de = ReadDir(mapping_dir, "pg_logical/mappings")) != NULL)
+	{
+		Oid			f_dboid;
+		Oid			f_relid;
+		TransactionId f_mapped_xid;
+		TransactionId f_create_xid;
+		XLogRecPtr	f_lsn;
+		uint32		f_hi,
+					f_lo;
+		RewriteMappingFile *f;
+
+		if (strcmp(mapping_de->d_name, ".") == 0 ||
+			strcmp(mapping_de->d_name, "..") == 0)
+			continue;
+
+		/* Ignore files that aren't ours */
+		if (strncmp(mapping_de->d_name, "map-", 4) != 0)
+			continue;
+
+		if (sscanf(mapping_de->d_name, LOGICAL_REWRITE_FORMAT,
+				   &f_dboid, &f_relid, &f_hi, &f_lo,
+				   &f_mapped_xid, &f_create_xid) != 6)
+			elog(ERROR, "could not parse filename \"%s\"", mapping_de->d_name);
+
+		f_lsn = ((uint64) f_hi) << 32 | f_lo;
+
+		/* mapping for another database */
+		if (f_dboid != dboid)
+			continue;
+
+		/* mapping for another relation */
+		if (f_relid != relid)
+			continue;
+
+		/* did the creating transaction abort? */
+		if (!TransactionIdDidCommit(f_create_xid))
+			continue;
+
+		/* not for our transaction */
+		if (!TransactionIdInArray(f_mapped_xid, snapshot->subxip, snapshot->subxcnt))
+			continue;
+
+		/* ok, relevant, queue for apply */
+		f = palloc(sizeof(RewriteMappingFile));
+		f->lsn = f_lsn;
+		strcpy(f->fname, mapping_de->d_name);
+		files = lappend(files, f);
+	}
+	FreeDir(mapping_dir);
+
+	/* sort files so we apply them in LSN order */
+	list_sort(files, file_sort_by_lsn);
+
+	foreach(file, files)
+	{
+		RewriteMappingFile *f = (RewriteMappingFile *) lfirst(file);
+
+		elog(DEBUG1, "applying mapping: \"%s\" in %u", f->fname,
+			 snapshot->subxip[0]);
+		ApplyLogicalMappingFile(tuplecid_data, relid, f->fname);
+		pfree(f);
+	}
+}
+
+/*
+ * Lookup cmin/cmax of a tuple, during logical decoding where we can't rely on
+ * combo CIDs.
+ */
+bool
+ResolveCminCmaxDuringDecoding(HTAB *tuplecid_data,
+							  Snapshot snapshot,
+							  HeapTuple htup, Buffer buffer,
+							  CommandId *cmin, CommandId *cmax)
+{
+	ReorderBufferTupleCidKey key;
+	ReorderBufferTupleCidEnt *ent;
+	ForkNumber	forkno;
+	BlockNumber blockno;
+	bool		updated_mapping = false;
+
+	/*
+	 * Return unresolved if tuplecid_data is not valid.  That's because when
+	 * streaming in-progress transactions we may run into tuples with the CID
+	 * before actually decoding them.  Think e.g. about INSERT followed by
+	 * TRUNCATE, where the TRUNCATE may not be decoded yet when applying the
+	 * INSERT.  So in such cases, we assume the CID is from the future
+	 * command.
+	 */
+	if (tuplecid_data == NULL)
+		return false;
+
+	/* be careful about padding */
+	memset(&key, 0, sizeof(key));
+
+	Assert(!BufferIsLocal(buffer));
+
+	/*
+	 * get relfilenode from the buffer, no convenient way to access it other
+	 * than that.
+	 */
+	BufferGetTag(buffer, &key.relnode, &forkno, &blockno);
+
+	/* tuples can only be in the main fork */
+	Assert(forkno == MAIN_FORKNUM);
+	Assert(blockno == ItemPointerGetBlockNumber(&htup->t_self));
+
+	ItemPointerCopy(&htup->t_self,
+					&key.tid);
+
+restart:
+	ent = (ReorderBufferTupleCidEnt *)
+		hash_search(tuplecid_data,
+					(void *) &key,
+					HASH_FIND,
+					NULL);
+
+	/*
+	 * failed to find a mapping, check whether the table was rewritten and
+	 * apply mapping if so, but only do that once - there can be no new
+	 * mappings while we are in here since we have to hold a lock on the
+	 * relation.
+	 */
+	if (ent == NULL && !updated_mapping)
+	{
+		UpdateLogicalMappings(tuplecid_data, htup->t_tableOid, snapshot);
+		/* now check but don't update for a mapping again */
+		updated_mapping = true;
+		goto restart;
+	}
+	else if (ent == NULL)
+		return false;
+
+	if (cmin)
+		*cmin = ent->cmin;
+	if (cmax)
+		*cmax = ent->cmax;
+	return true;
+}
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
new file mode 100644
index 0000000..6df6024
--- /dev/null
+++ b/src/backend/replication/logical/snapbuild.c
@@ -0,0 +1,1995 @@
+/*-------------------------------------------------------------------------
+ *
+ * snapbuild.c
+ *
+ *	  Infrastructure for building historic catalog snapshots based on contents
+ *	  of the WAL, for the purpose of decoding heapam.c style values in the
+ *	  WAL.
+ *
+ * NOTES:
+ *
+ * We build snapshots which can *only* be used to read catalog contents and we
+ * do so by reading and interpreting the WAL stream. The aim is to build a
+ * snapshot that behaves the same as a freshly taken MVCC snapshot would have
+ * at the time the XLogRecord was generated.
+ *
+ * To build the snapshots we reuse the infrastructure built for Hot
+ * Standby. The in-memory snapshots we build look different than HS' because
+ * we have different needs. To successfully decode data from the WAL we only
+ * need to access catalog tables and (sys|rel|cat)cache, not the actual user
+ * tables since the data we decode is wholly contained in the WAL
+ * records. Also, our snapshots need to be different in comparison to normal
+ * MVCC ones because in contrast to those we cannot fully rely on the clog and
+ * pg_subtrans for information about committed transactions because they might
+ * commit in the future from the POV of the WAL entry we're currently
+ * decoding. This definition has the advantage that we only need to prevent
+ * removal of catalog rows, while normal table's rows can still be
+ * removed. This is achieved by using the replication slot mechanism.
+ *
+ * As the percentage of transactions modifying the catalog normally is fairly
+ * small in comparisons to ones only manipulating user data, we keep track of
+ * the committed catalog modifying ones inside [xmin, xmax) instead of keeping
+ * track of all running transactions like it's done in a normal snapshot. Note
+ * that we're generally only looking at transactions that have acquired an
+ * xid. That is we keep a list of transactions between snapshot->(xmin, xmax)
+ * that we consider committed, everything else is considered aborted/in
+ * progress. That also allows us not to care about subtransactions before they
+ * have committed which means this module, in contrast to HS, doesn't have to
+ * care about suboverflowed subtransactions and similar.
+ *
+ * One complexity of doing this is that to e.g. handle mixed DDL/DML
+ * transactions we need Snapshots that see intermediate versions of the
+ * catalog in a transaction. During normal operation this is achieved by using
+ * CommandIds/cmin/cmax. The problem with that however is that for space
+ * efficiency reasons only one value of that is stored
+ * (cf. combocid.c). Since combo CIDs are only available in memory we log
+ * additional information which allows us to get the original (cmin, cmax)
+ * pair during visibility checks. Check the reorderbuffer.c's comment above
+ * ResolveCminCmaxDuringDecoding() for details.
+ *
+ * To facilitate all this we need our own visibility routine, as the normal
+ * ones are optimized for different usecases.
+ *
+ * To replace the normal catalog snapshots with decoding ones use the
+ * SetupHistoricSnapshot() and TeardownHistoricSnapshot() functions.
+ *
+ *
+ *
+ * The snapbuild machinery is starting up in several stages, as illustrated
+ * by the following graph describing the SnapBuild->state transitions:
+ *
+ *		   +-------------------------+
+ *	  +----|		 START			 |-------------+
+ *	  |    +-------------------------+			   |
+ *	  |					|						   |
+ *	  |					|						   |
+ *	  |		   running_xacts #1					   |
+ *	  |					|						   |
+ *	  |					|						   |
+ *	  |					v						   |
+ *	  |    +-------------------------+			   v
+ *	  |    |   BUILDING_SNAPSHOT	 |------------>|
+ *	  |    +-------------------------+			   |
+ *	  |					|						   |
+ *	  |					|						   |
+ *	  | running_xacts #2, xacts from #1 finished   |
+ *	  |					|						   |
+ *	  |					|						   |
+ *	  |					v						   |
+ *	  |    +-------------------------+			   v
+ *	  |    |	   FULL_SNAPSHOT	 |------------>|
+ *	  |    +-------------------------+			   |
+ *	  |					|						   |
+ * running_xacts		|					   saved snapshot
+ * with zero xacts		|				  at running_xacts's lsn
+ *	  |					|						   |
+ *	  | running_xacts with xacts from #2 finished  |
+ *	  |					|						   |
+ *	  |					v						   |
+ *	  |    +-------------------------+			   |
+ *	  +--->|SNAPBUILD_CONSISTENT	 |<------------+
+ *		   +-------------------------+
+ *
+ * Initially the machinery is in the START stage. When an xl_running_xacts
+ * record is read that is sufficiently new (above the safe xmin horizon),
+ * there's a state transition. If there were no running xacts when the
+ * running_xacts record was generated, we'll directly go into CONSISTENT
+ * state, otherwise we'll switch to the BUILDING_SNAPSHOT state. Having a full
+ * snapshot means that all transactions that start henceforth can be decoded
+ * in their entirety, but transactions that started previously can't. In
+ * FULL_SNAPSHOT we'll switch into CONSISTENT once all those previously
+ * running transactions have committed or aborted.
+ *
+ * Only transactions that commit after CONSISTENT state has been reached will
+ * be replayed, even though they might have started while still in
+ * FULL_SNAPSHOT. That ensures that we'll reach a point where no previous
+ * changes has been exported, but all the following ones will be. That point
+ * is a convenient point to initialize replication from, which is why we
+ * export a snapshot at that point, which *can* be used to read normal data.
+ *
+ * Copyright (c) 2012-2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/snapbuild.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include "access/heapam_xlog.h"
+#include "access/transam.h"
+#include "access/xact.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "replication/logical.h"
+#include "replication/reorderbuffer.h"
+#include "replication/snapbuild.h"
+#include "storage/block.h"		/* debugging output */
+#include "storage/fd.h"
+#include "storage/lmgr.h"
+#include "storage/proc.h"
+#include "storage/procarray.h"
+#include "storage/standby.h"
+#include "utils/builtins.h"
+#include "utils/memutils.h"
+#include "utils/snapmgr.h"
+#include "utils/snapshot.h"
+
+/*
+ * This struct contains the current state of the snapshot building
+ * machinery. Besides a forward declaration in the header, it is not exposed
+ * to the public, so we can easily change its contents.
+ */
+struct SnapBuild
+{
+	/* how far are we along building our first full snapshot */
+	SnapBuildState state;
+
+	/* private memory context used to allocate memory for this module. */
+	MemoryContext context;
+
+	/* all transactions < than this have committed/aborted */
+	TransactionId xmin;
+
+	/* all transactions >= than this are uncommitted */
+	TransactionId xmax;
+
+	/*
+	 * Don't replay commits from an LSN < this LSN. This can be set externally
+	 * but it will also be advanced (never retreat) from within snapbuild.c.
+	 */
+	XLogRecPtr	start_decoding_at;
+
+	/*
+	 * LSN at which we found a consistent point at the time of slot creation.
+	 * This is also the point where we have exported a snapshot for the
+	 * initial copy.
+	 *
+	 * The prepared transactions that are not covered by initial snapshot
+	 * needs to be sent later along with commit prepared and they must be
+	 * before this point.
+	 */
+	XLogRecPtr	initial_consistent_point;
+
+	/*
+	 * Don't start decoding WAL until the "xl_running_xacts" information
+	 * indicates there are no running xids with an xid smaller than this.
+	 */
+	TransactionId initial_xmin_horizon;
+
+	/* Indicates if we are building full snapshot or just catalog one. */
+	bool		building_full_snapshot;
+
+	/*
+	 * Snapshot that's valid to see the catalog state seen at this moment.
+	 */
+	Snapshot	snapshot;
+
+	/*
+	 * LSN of the last location we are sure a snapshot has been serialized to.
+	 */
+	XLogRecPtr	last_serialized_snapshot;
+
+	/*
+	 * The reorderbuffer we need to update with usable snapshots et al.
+	 */
+	ReorderBuffer *reorder;
+
+	/*
+	 * TransactionId at which the next phase of initial snapshot building will
+	 * happen. InvalidTransactionId if not known (i.e. SNAPBUILD_START), or
+	 * when no next phase necessary (SNAPBUILD_CONSISTENT).
+	 */
+	TransactionId next_phase_at;
+
+	/*
+	 * Array of transactions which could have catalog changes that committed
+	 * between xmin and xmax.
+	 */
+	struct
+	{
+		/* number of committed transactions */
+		size_t		xcnt;
+
+		/* available space for committed transactions */
+		size_t		xcnt_space;
+
+		/*
+		 * Until we reach a CONSISTENT state, we record commits of all
+		 * transactions, not just the catalog changing ones. Record when that
+		 * changes so we know we cannot export a snapshot safely anymore.
+		 */
+		bool		includes_all_transactions;
+
+		/*
+		 * Array of committed transactions that have modified the catalog.
+		 *
+		 * As this array is frequently modified we do *not* keep it in
+		 * xidComparator order. Instead we sort the array when building &
+		 * distributing a snapshot.
+		 *
+		 * TODO: It's unclear whether that reasoning has much merit. Every
+		 * time we add something here after becoming consistent will also
+		 * require distributing a snapshot. Storing them sorted would
+		 * potentially also make it easier to purge (but more complicated wrt
+		 * wraparound?). Should be improved if sorting while building the
+		 * snapshot shows up in profiles.
+		 */
+		TransactionId *xip;
+	}			committed;
+};
+
+/*
+ * Starting a transaction -- which we need to do while exporting a snapshot --
+ * removes knowledge about the previously used resowner, so we save it here.
+ */
+static ResourceOwner SavedResourceOwnerDuringExport = NULL;
+static bool ExportInProgress = false;
+
+/* ->committed manipulation */
+static void SnapBuildPurgeCommittedTxn(SnapBuild *builder);
+
+/* snapshot building/manipulation/distribution functions */
+static Snapshot SnapBuildBuildSnapshot(SnapBuild *builder);
+
+static void SnapBuildFreeSnapshot(Snapshot snap);
+
+static void SnapBuildSnapIncRefcount(Snapshot snap);
+
+static void SnapBuildDistributeNewCatalogSnapshot(SnapBuild *builder, XLogRecPtr lsn);
+
+/* xlog reading helper functions for SnapBuildProcessRunningXacts */
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
+
+/* serialization functions */
+static void SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn);
+static bool SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn);
+
+/*
+ * Allocate a new snapshot builder.
+ *
+ * xmin_horizon is the xid >= which we can be sure no catalog rows have been
+ * removed, start_lsn is the LSN >= we want to replay commits.
+ */
+SnapBuild *
+AllocateSnapshotBuilder(ReorderBuffer *reorder,
+						TransactionId xmin_horizon,
+						XLogRecPtr start_lsn,
+						bool need_full_snapshot,
+						XLogRecPtr initial_consistent_point)
+{
+	MemoryContext context;
+	MemoryContext oldcontext;
+	SnapBuild  *builder;
+
+	/* allocate memory in own context, to have better accountability */
+	context = AllocSetContextCreate(CurrentMemoryContext,
+									"snapshot builder context",
+									ALLOCSET_DEFAULT_SIZES);
+	oldcontext = MemoryContextSwitchTo(context);
+
+	builder = palloc0(sizeof(SnapBuild));
+
+	builder->state = SNAPBUILD_START;
+	builder->context = context;
+	builder->reorder = reorder;
+	/* Other struct members initialized by zeroing via palloc0 above */
+
+	builder->committed.xcnt = 0;
+	builder->committed.xcnt_space = 128;	/* arbitrary number */
+	builder->committed.xip =
+		palloc0(builder->committed.xcnt_space * sizeof(TransactionId));
+	builder->committed.includes_all_transactions = true;
+
+	builder->initial_xmin_horizon = xmin_horizon;
+	builder->start_decoding_at = start_lsn;
+	builder->building_full_snapshot = need_full_snapshot;
+	builder->initial_consistent_point = initial_consistent_point;
+
+	MemoryContextSwitchTo(oldcontext);
+
+	return builder;
+}
+
+/*
+ * Free a snapshot builder.
+ */
+void
+FreeSnapshotBuilder(SnapBuild *builder)
+{
+	MemoryContext context = builder->context;
+
+	/* free snapshot explicitly, that contains some error checking */
+	if (builder->snapshot != NULL)
+	{
+		SnapBuildSnapDecRefcount(builder->snapshot);
+		builder->snapshot = NULL;
+	}
+
+	/* other resources are deallocated via memory context reset */
+	MemoryContextDelete(context);
+}
+
+/*
+ * Free an unreferenced snapshot that has previously been built by us.
+ */
+static void
+SnapBuildFreeSnapshot(Snapshot snap)
+{
+	/* make sure we don't get passed an external snapshot */
+	Assert(snap->snapshot_type == SNAPSHOT_HISTORIC_MVCC);
+
+	/* make sure nobody modified our snapshot */
+	Assert(snap->curcid == FirstCommandId);
+	Assert(!snap->suboverflowed);
+	Assert(!snap->takenDuringRecovery);
+	Assert(snap->regd_count == 0);
+
+	/* slightly more likely, so it's checked even without c-asserts */
+	if (snap->copied)
+		elog(ERROR, "cannot free a copied snapshot");
+
+	if (snap->active_count)
+		elog(ERROR, "cannot free an active snapshot");
+
+	pfree(snap);
+}
+
+/*
+ * In which state of snapshot building are we?
+ */
+SnapBuildState
+SnapBuildCurrentState(SnapBuild *builder)
+{
+	return builder->state;
+}
+
+/*
+ * Return the LSN at which the snapshot was exported
+ */
+XLogRecPtr
+SnapBuildInitialConsistentPoint(SnapBuild *builder)
+{
+	return builder->initial_consistent_point;
+}
+
+/*
+ * Should the contents of transaction ending at 'ptr' be decoded?
+ */
+bool
+SnapBuildXactNeedsSkip(SnapBuild *builder, XLogRecPtr ptr)
+{
+	return ptr < builder->start_decoding_at;
+}
+
+/*
+ * Increase refcount of a snapshot.
+ *
+ * This is used when handing out a snapshot to some external resource or when
+ * adding a Snapshot as builder->snapshot.
+ */
+static void
+SnapBuildSnapIncRefcount(Snapshot snap)
+{
+	snap->active_count++;
+}
+
+/*
+ * Decrease refcount of a snapshot and free if the refcount reaches zero.
+ *
+ * Externally visible, so that external resources that have been handed an
+ * IncRef'ed Snapshot can adjust its refcount easily.
+ */
+void
+SnapBuildSnapDecRefcount(Snapshot snap)
+{
+	/* make sure we don't get passed an external snapshot */
+	Assert(snap->snapshot_type == SNAPSHOT_HISTORIC_MVCC);
+
+	/* make sure nobody modified our snapshot */
+	Assert(snap->curcid == FirstCommandId);
+	Assert(!snap->suboverflowed);
+	Assert(!snap->takenDuringRecovery);
+
+	Assert(snap->regd_count == 0);
+
+	Assert(snap->active_count > 0);
+
+	/* slightly more likely, so it's checked even without casserts */
+	if (snap->copied)
+		elog(ERROR, "cannot free a copied snapshot");
+
+	snap->active_count--;
+	if (snap->active_count == 0)
+		SnapBuildFreeSnapshot(snap);
+}
+
+/*
+ * Build a new snapshot, based on currently committed catalog-modifying
+ * transactions.
+ *
+ * In-progress transactions with catalog access are *not* allowed to modify
+ * these snapshots; they have to copy them and fill in appropriate ->curcid
+ * and ->subxip/subxcnt values.
+ */
+static Snapshot
+SnapBuildBuildSnapshot(SnapBuild *builder)
+{
+	Snapshot	snapshot;
+	Size		ssize;
+
+	Assert(builder->state >= SNAPBUILD_FULL_SNAPSHOT);
+
+	ssize = sizeof(SnapshotData)
+		+ sizeof(TransactionId) * builder->committed.xcnt
+		+ sizeof(TransactionId) * 1 /* toplevel xid */ ;
+
+	snapshot = MemoryContextAllocZero(builder->context, ssize);
+
+	snapshot->snapshot_type = SNAPSHOT_HISTORIC_MVCC;
+
+	/*
+	 * We misuse the original meaning of SnapshotData's xip and subxip fields
+	 * to make the more fitting for our needs.
+	 *
+	 * In the 'xip' array we store transactions that have to be treated as
+	 * committed. Since we will only ever look at tuples from transactions
+	 * that have modified the catalog it's more efficient to store those few
+	 * that exist between xmin and xmax (frequently there are none).
+	 *
+	 * Snapshots that are used in transactions that have modified the catalog
+	 * also use the 'subxip' array to store their toplevel xid and all the
+	 * subtransaction xids so we can recognize when we need to treat rows as
+	 * visible that are not in xip but still need to be visible. Subxip only
+	 * gets filled when the transaction is copied into the context of a
+	 * catalog modifying transaction since we otherwise share a snapshot
+	 * between transactions. As long as a txn hasn't modified the catalog it
+	 * doesn't need to treat any uncommitted rows as visible, so there is no
+	 * need for those xids.
+	 *
+	 * Both arrays are qsort'ed so that we can use bsearch() on them.
+	 */
+	Assert(TransactionIdIsNormal(builder->xmin));
+	Assert(TransactionIdIsNormal(builder->xmax));
+
+	snapshot->xmin = builder->xmin;
+	snapshot->xmax = builder->xmax;
+
+	/* store all transactions to be treated as committed by this snapshot */
+	snapshot->xip =
+		(TransactionId *) ((char *) snapshot + sizeof(SnapshotData));
+	snapshot->xcnt = builder->committed.xcnt;
+	memcpy(snapshot->xip,
+		   builder->committed.xip,
+		   builder->committed.xcnt * sizeof(TransactionId));
+
+	/* sort so we can bsearch() */
+	qsort(snapshot->xip, snapshot->xcnt, sizeof(TransactionId), xidComparator);
+
+	/*
+	 * Initially, subxip is empty, i.e. it's a snapshot to be used by
+	 * transactions that don't modify the catalog. Will be filled by
+	 * ReorderBufferCopySnap() if necessary.
+	 */
+	snapshot->subxcnt = 0;
+	snapshot->subxip = NULL;
+
+	snapshot->suboverflowed = false;
+	snapshot->takenDuringRecovery = false;
+	snapshot->copied = false;
+	snapshot->curcid = FirstCommandId;
+	snapshot->active_count = 0;
+	snapshot->regd_count = 0;
+	snapshot->snapXactCompletionCount = 0;
+
+	return snapshot;
+}
+
+/*
+ * Build the initial slot snapshot and convert it to a normal snapshot that
+ * is understood by HeapTupleSatisfiesMVCC.
+ *
+ * The snapshot will be usable directly in current transaction or exported
+ * for loading in different transaction.
+ */
+Snapshot
+SnapBuildInitialSnapshot(SnapBuild *builder)
+{
+	Snapshot	snap;
+	TransactionId xid;
+	TransactionId *newxip;
+	int			newxcnt = 0;
+
+	Assert(!FirstSnapshotSet);
+	Assert(XactIsoLevel == XACT_REPEATABLE_READ);
+
+	if (builder->state != SNAPBUILD_CONSISTENT)
+		elog(ERROR, "cannot build an initial slot snapshot before reaching a consistent state");
+
+	if (!builder->committed.includes_all_transactions)
+		elog(ERROR, "cannot build an initial slot snapshot, not all transactions are monitored anymore");
+
+	/* so we don't overwrite the existing value */
+	if (TransactionIdIsValid(MyProc->xmin))
+		elog(ERROR, "cannot build an initial slot snapshot when MyProc->xmin already is valid");
+
+	snap = SnapBuildBuildSnapshot(builder);
+
+	/*
+	 * We know that snap->xmin is alive, enforced by the logical xmin
+	 * mechanism. Due to that we can do this without locks, we're only
+	 * changing our own value.
+	 */
+#ifdef USE_ASSERT_CHECKING
+	{
+		TransactionId safeXid;
+
+		LWLockAcquire(ProcArrayLock, LW_SHARED);
+		safeXid = GetOldestSafeDecodingTransactionId(false);
+		LWLockRelease(ProcArrayLock);
+
+		Assert(TransactionIdPrecedesOrEquals(safeXid, snap->xmin));
+	}
+#endif
+
+	MyProc->xmin = snap->xmin;
+
+	/* allocate in transaction context */
+	newxip = (TransactionId *)
+		palloc(sizeof(TransactionId) * GetMaxSnapshotXidCount());
+
+	/*
+	 * snapbuild.c builds transactions in an "inverted" manner, which means it
+	 * stores committed transactions in ->xip, not ones in progress. Build a
+	 * classical snapshot by marking all non-committed transactions as
+	 * in-progress. This can be expensive.
+	 */
+	for (xid = snap->xmin; NormalTransactionIdPrecedes(xid, snap->xmax);)
+	{
+		void	   *test;
+
+		/*
+		 * Check whether transaction committed using the decoding snapshot
+		 * meaning of ->xip.
+		 */
+		test = bsearch(&xid, snap->xip, snap->xcnt,
+					   sizeof(TransactionId), xidComparator);
+
+		if (test == NULL)
+		{
+			if (newxcnt >= GetMaxSnapshotXidCount())
+				ereport(ERROR,
+						(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
+						 errmsg("initial slot snapshot too large")));
+
+			newxip[newxcnt++] = xid;
+		}
+
+		TransactionIdAdvance(xid);
+	}
+
+	/* adjust remaining snapshot fields as needed */
+	snap->snapshot_type = SNAPSHOT_MVCC;
+	snap->xcnt = newxcnt;
+	snap->xip = newxip;
+
+	return snap;
+}
+
+/*
+ * Export a snapshot so it can be set in another session with SET TRANSACTION
+ * SNAPSHOT.
+ *
+ * For that we need to start a transaction in the current backend as the
+ * importing side checks whether the source transaction is still open to make
+ * sure the xmin horizon hasn't advanced since then.
+ */
+const char *
+SnapBuildExportSnapshot(SnapBuild *builder)
+{
+	Snapshot	snap;
+	char	   *snapname;
+
+	if (IsTransactionOrTransactionBlock())
+		elog(ERROR, "cannot export a snapshot from within a transaction");
+
+	if (SavedResourceOwnerDuringExport)
+		elog(ERROR, "can only export one snapshot at a time");
+
+	SavedResourceOwnerDuringExport = CurrentResourceOwner;
+	ExportInProgress = true;
+
+	StartTransactionCommand();
+
+	/* There doesn't seem to a nice API to set these */
+	XactIsoLevel = XACT_REPEATABLE_READ;
+	XactReadOnly = true;
+
+	snap = SnapBuildInitialSnapshot(builder);
+
+	/*
+	 * now that we've built a plain snapshot, make it active and use the
+	 * normal mechanisms for exporting it
+	 */
+	snapname = ExportSnapshot(snap);
+
+	ereport(LOG,
+			(errmsg_plural("exported logical decoding snapshot: \"%s\" with %u transaction ID",
+						   "exported logical decoding snapshot: \"%s\" with %u transaction IDs",
+						   snap->xcnt,
+						   snapname, snap->xcnt)));
+	return snapname;
+}
+
+/*
+ * Ensure there is a snapshot and if not build one for current transaction.
+ */
+Snapshot
+SnapBuildGetOrBuildSnapshot(SnapBuild *builder, TransactionId xid)
+{
+	Assert(builder->state == SNAPBUILD_CONSISTENT);
+
+	/* only build a new snapshot if we don't have a prebuilt one */
+	if (builder->snapshot == NULL)
+	{
+		builder->snapshot = SnapBuildBuildSnapshot(builder);
+		/* increase refcount for the snapshot builder */
+		SnapBuildSnapIncRefcount(builder->snapshot);
+	}
+
+	return builder->snapshot;
+}
+
+/*
+ * Reset a previously SnapBuildExportSnapshot()'ed snapshot if there is
+ * any. Aborts the previously started transaction and resets the resource
+ * owner back to its original value.
+ */
+void
+SnapBuildClearExportedSnapshot(void)
+{
+	ResourceOwner tmpResOwner;
+
+	/* nothing exported, that is the usual case */
+	if (!ExportInProgress)
+		return;
+
+	if (!IsTransactionState())
+		elog(ERROR, "clearing exported snapshot in wrong transaction state");
+
+	/*
+	 * AbortCurrentTransaction() takes care of resetting the snapshot state,
+	 * so remember SavedResourceOwnerDuringExport.
+	 */
+	tmpResOwner = SavedResourceOwnerDuringExport;
+
+	/* make sure nothing could have ever happened */
+	AbortCurrentTransaction();
+
+	CurrentResourceOwner = tmpResOwner;
+}
+
+/*
+ * Clear snapshot export state during transaction abort.
+ */
+void
+SnapBuildResetExportedSnapshotState(void)
+{
+	SavedResourceOwnerDuringExport = NULL;
+	ExportInProgress = false;
+}
+
+/*
+ * Handle the effects of a single heap change, appropriate to the current state
+ * of the snapshot builder and returns whether changes made at (xid, lsn) can
+ * be decoded.
+ */
+bool
+SnapBuildProcessChange(SnapBuild *builder, TransactionId xid, XLogRecPtr lsn)
+{
+	/*
+	 * We can't handle data in transactions if we haven't built a snapshot
+	 * yet, so don't store them.
+	 */
+	if (builder->state < SNAPBUILD_FULL_SNAPSHOT)
+		return false;
+
+	/*
+	 * No point in keeping track of changes in transactions that we don't have
+	 * enough information about to decode. This means that they started before
+	 * we got into the SNAPBUILD_FULL_SNAPSHOT state.
+	 */
+	if (builder->state < SNAPBUILD_CONSISTENT &&
+		TransactionIdPrecedes(xid, builder->next_phase_at))
+		return false;
+
+	/*
+	 * If the reorderbuffer doesn't yet have a snapshot, add one now, it will
+	 * be needed to decode the change we're currently processing.
+	 */
+	if (!ReorderBufferXidHasBaseSnapshot(builder->reorder, xid))
+	{
+		/* only build a new snapshot if we don't have a prebuilt one */
+		if (builder->snapshot == NULL)
+		{
+			builder->snapshot = SnapBuildBuildSnapshot(builder);
+			/* increase refcount for the snapshot builder */
+			SnapBuildSnapIncRefcount(builder->snapshot);
+		}
+
+		/*
+		 * Increase refcount for the transaction we're handing the snapshot
+		 * out to.
+		 */
+		SnapBuildSnapIncRefcount(builder->snapshot);
+		ReorderBufferSetBaseSnapshot(builder->reorder, xid, lsn,
+									 builder->snapshot);
+	}
+
+	return true;
+}
+
+/*
+ * Do CommandId/combo CID handling after reading an xl_heap_new_cid record.
+ * This implies that a transaction has done some form of write to system
+ * catalogs.
+ */
+void
+SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
+					   XLogRecPtr lsn, xl_heap_new_cid *xlrec)
+{
+	CommandId	cid;
+
+	/*
+	 * we only log new_cid's if a catalog tuple was modified, so mark the
+	 * transaction as containing catalog modifications
+	 */
+	ReorderBufferXidSetCatalogChanges(builder->reorder, xid, lsn);
+
+	ReorderBufferAddNewTupleCids(builder->reorder, xlrec->top_xid, lsn,
+								 xlrec->target_node, xlrec->target_tid,
+								 xlrec->cmin, xlrec->cmax,
+								 xlrec->combocid);
+
+	/* figure out new command id */
+	if (xlrec->cmin != InvalidCommandId &&
+		xlrec->cmax != InvalidCommandId)
+		cid = Max(xlrec->cmin, xlrec->cmax);
+	else if (xlrec->cmax != InvalidCommandId)
+		cid = xlrec->cmax;
+	else if (xlrec->cmin != InvalidCommandId)
+		cid = xlrec->cmin;
+	else
+	{
+		cid = InvalidCommandId; /* silence compiler */
+		elog(ERROR, "xl_heap_new_cid record without a valid CommandId");
+	}
+
+	ReorderBufferAddNewCommandId(builder->reorder, xid, lsn, cid + 1);
+}
+
+/*
+ * Add a new Snapshot to all transactions we're decoding that currently are
+ * in-progress so they can see new catalog contents made by the transaction
+ * that just committed. This is necessary because those in-progress
+ * transactions will use the new catalog's contents from here on (at the very
+ * least everything they do needs to be compatible with newer catalog
+ * contents).
+ */
+static void
+SnapBuildDistributeNewCatalogSnapshot(SnapBuild *builder, XLogRecPtr lsn)
+{
+	dlist_iter	txn_i;
+	ReorderBufferTXN *txn;
+
+	/*
+	 * Iterate through all toplevel transactions. This can include
+	 * subtransactions which we just don't yet know to be that, but that's
+	 * fine, they will just get an unnecessary snapshot queued.
+	 */
+	dlist_foreach(txn_i, &builder->reorder->toplevel_by_lsn)
+	{
+		txn = dlist_container(ReorderBufferTXN, node, txn_i.cur);
+
+		Assert(TransactionIdIsValid(txn->xid));
+
+		/*
+		 * If we don't have a base snapshot yet, there are no changes in this
+		 * transaction which in turn implies we don't yet need a snapshot at
+		 * all. We'll add a snapshot when the first change gets queued.
+		 *
+		 * NB: This works correctly even for subtransactions because
+		 * ReorderBufferAssignChild() takes care to transfer the base snapshot
+		 * to the top-level transaction, and while iterating the changequeue
+		 * we'll get the change from the subtxn.
+		 */
+		if (!ReorderBufferXidHasBaseSnapshot(builder->reorder, txn->xid))
+			continue;
+
+		/*
+		 * We don't need to add snapshot to prepared transactions as they
+		 * should not see the new catalog contents.
+		 */
+		if (rbtxn_prepared(txn) || rbtxn_skip_prepared(txn))
+			continue;
+
+		elog(DEBUG2, "adding a new snapshot to %u at %X/%X",
+			 txn->xid, LSN_FORMAT_ARGS(lsn));
+
+		/*
+		 * increase the snapshot's refcount for the transaction we are handing
+		 * it out to
+		 */
+		SnapBuildSnapIncRefcount(builder->snapshot);
+		ReorderBufferAddSnapshot(builder->reorder, txn->xid, lsn,
+								 builder->snapshot);
+	}
+}
+
+/*
+ * Keep track of a new catalog changing transaction that has committed.
+ */
+static void
+SnapBuildAddCommittedTxn(SnapBuild *builder, TransactionId xid)
+{
+	Assert(TransactionIdIsValid(xid));
+
+	if (builder->committed.xcnt == builder->committed.xcnt_space)
+	{
+		builder->committed.xcnt_space = builder->committed.xcnt_space * 2 + 1;
+
+		elog(DEBUG1, "increasing space for committed transactions to %u",
+			 (uint32) builder->committed.xcnt_space);
+
+		builder->committed.xip = repalloc(builder->committed.xip,
+										  builder->committed.xcnt_space * sizeof(TransactionId));
+	}
+
+	/*
+	 * TODO: It might make sense to keep the array sorted here instead of
+	 * doing it every time we build a new snapshot. On the other hand this
+	 * gets called repeatedly when a transaction with subtransactions commits.
+	 */
+	builder->committed.xip[builder->committed.xcnt++] = xid;
+}
+
+/*
+ * Remove knowledge about transactions we treat as committed that are smaller
+ * than ->xmin. Those won't ever get checked via the ->committed array but via
+ * the clog machinery, so we don't need to waste memory on them.
+ */
+static void
+SnapBuildPurgeCommittedTxn(SnapBuild *builder)
+{
+	int			off;
+	TransactionId *workspace;
+	int			surviving_xids = 0;
+
+	/* not ready yet */
+	if (!TransactionIdIsNormal(builder->xmin))
+		return;
+
+	/* TODO: Neater algorithm than just copying and iterating? */
+	workspace =
+		MemoryContextAlloc(builder->context,
+						   builder->committed.xcnt * sizeof(TransactionId));
+
+	/* copy xids that still are interesting to workspace */
+	for (off = 0; off < builder->committed.xcnt; off++)
+	{
+		if (NormalTransactionIdPrecedes(builder->committed.xip[off],
+										builder->xmin))
+			;					/* remove */
+		else
+			workspace[surviving_xids++] = builder->committed.xip[off];
+	}
+
+	/* copy workspace back to persistent state */
+	memcpy(builder->committed.xip, workspace,
+		   surviving_xids * sizeof(TransactionId));
+
+	elog(DEBUG3, "purged committed transactions from %u to %u, xmin: %u, xmax: %u",
+		 (uint32) builder->committed.xcnt, (uint32) surviving_xids,
+		 builder->xmin, builder->xmax);
+	builder->committed.xcnt = surviving_xids;
+
+	pfree(workspace);
+}
+
+/*
+ * Handle everything that needs to be done when a transaction commits
+ */
+void
+SnapBuildCommitTxn(SnapBuild *builder, XLogRecPtr lsn, TransactionId xid,
+				   int nsubxacts, TransactionId *subxacts)
+{
+	int			nxact;
+
+	bool		needs_snapshot = false;
+	bool		needs_timetravel = false;
+	bool		sub_needs_timetravel = false;
+
+	TransactionId xmax = xid;
+
+	/*
+	 * Transactions preceding BUILDING_SNAPSHOT will neither be decoded, nor
+	 * will they be part of a snapshot.  So we don't need to record anything.
+	 */
+	if (builder->state == SNAPBUILD_START ||
+		(builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
+		 TransactionIdPrecedes(xid, builder->next_phase_at)))
+	{
+		/* ensure that only commits after this are getting replayed */
+		if (builder->start_decoding_at <= lsn)
+			builder->start_decoding_at = lsn + 1;
+		return;
+	}
+
+	if (builder->state < SNAPBUILD_CONSISTENT)
+	{
+		/* ensure that only commits after this are getting replayed */
+		if (builder->start_decoding_at <= lsn)
+			builder->start_decoding_at = lsn + 1;
+
+		/*
+		 * If building an exportable snapshot, force xid to be tracked, even
+		 * if the transaction didn't modify the catalog.
+		 */
+		if (builder->building_full_snapshot)
+		{
+			needs_timetravel = true;
+		}
+	}
+
+	for (nxact = 0; nxact < nsubxacts; nxact++)
+	{
+		TransactionId subxid = subxacts[nxact];
+
+		/*
+		 * Add subtransaction to base snapshot if catalog modifying, we don't
+		 * distinguish to toplevel transactions there.
+		 */
+		if (ReorderBufferXidHasCatalogChanges(builder->reorder, subxid))
+		{
+			sub_needs_timetravel = true;
+			needs_snapshot = true;
+
+			elog(DEBUG1, "found subtransaction %u:%u with catalog changes",
+				 xid, subxid);
+
+			SnapBuildAddCommittedTxn(builder, subxid);
+
+			if (NormalTransactionIdFollows(subxid, xmax))
+				xmax = subxid;
+		}
+
+		/*
+		 * If we're forcing timetravel we also need visibility information
+		 * about subtransaction, so keep track of subtransaction's state, even
+		 * if not catalog modifying.  Don't need to distribute a snapshot in
+		 * that case.
+		 */
+		else if (needs_timetravel)
+		{
+			SnapBuildAddCommittedTxn(builder, subxid);
+			if (NormalTransactionIdFollows(subxid, xmax))
+				xmax = subxid;
+		}
+	}
+
+	/* if top-level modified catalog, it'll need a snapshot */
+	if (ReorderBufferXidHasCatalogChanges(builder->reorder, xid))
+	{
+		elog(DEBUG2, "found top level transaction %u, with catalog changes",
+			 xid);
+		needs_snapshot = true;
+		needs_timetravel = true;
+		SnapBuildAddCommittedTxn(builder, xid);
+	}
+	else if (sub_needs_timetravel)
+	{
+		/* track toplevel txn as well, subxact alone isn't meaningful */
+		SnapBuildAddCommittedTxn(builder, xid);
+	}
+	else if (needs_timetravel)
+	{
+		elog(DEBUG2, "forced transaction %u to do timetravel", xid);
+
+		SnapBuildAddCommittedTxn(builder, xid);
+	}
+
+	if (!needs_timetravel)
+	{
+		/* record that we cannot export a general snapshot anymore */
+		builder->committed.includes_all_transactions = false;
+	}
+
+	Assert(!needs_snapshot || needs_timetravel);
+
+	/*
+	 * Adjust xmax of the snapshot builder, we only do that for committed,
+	 * catalog modifying, transactions, everything else isn't interesting for
+	 * us since we'll never look at the respective rows.
+	 */
+	if (needs_timetravel &&
+		(!TransactionIdIsValid(builder->xmax) ||
+		 TransactionIdFollowsOrEquals(xmax, builder->xmax)))
+	{
+		builder->xmax = xmax;
+		TransactionIdAdvance(builder->xmax);
+	}
+
+	/* if there's any reason to build a historic snapshot, do so now */
+	if (needs_snapshot)
+	{
+		/*
+		 * If we haven't built a complete snapshot yet there's no need to hand
+		 * it out, it wouldn't (and couldn't) be used anyway.
+		 */
+		if (builder->state < SNAPBUILD_FULL_SNAPSHOT)
+			return;
+
+		/*
+		 * Decrease the snapshot builder's refcount of the old snapshot, note
+		 * that it still will be used if it has been handed out to the
+		 * reorderbuffer earlier.
+		 */
+		if (builder->snapshot)
+			SnapBuildSnapDecRefcount(builder->snapshot);
+
+		builder->snapshot = SnapBuildBuildSnapshot(builder);
+
+		/* we might need to execute invalidations, add snapshot */
+		if (!ReorderBufferXidHasBaseSnapshot(builder->reorder, xid))
+		{
+			SnapBuildSnapIncRefcount(builder->snapshot);
+			ReorderBufferSetBaseSnapshot(builder->reorder, xid, lsn,
+										 builder->snapshot);
+		}
+
+		/* refcount of the snapshot builder for the new snapshot */
+		SnapBuildSnapIncRefcount(builder->snapshot);
+
+		/* add a new catalog snapshot to all currently running transactions */
+		SnapBuildDistributeNewCatalogSnapshot(builder, lsn);
+	}
+}
+
+
+/* -----------------------------------
+ * Snapshot building functions dealing with xlog records
+ * -----------------------------------
+ */
+
+/*
+ * Process a running xacts record, and use its information to first build a
+ * historic snapshot and later to release resources that aren't needed
+ * anymore.
+ */
+void
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+{
+	ReorderBufferTXN *txn;
+	TransactionId xmin;
+
+	/*
+	 * If we're not consistent yet, inspect the record to see whether it
+	 * allows to get closer to being consistent. If we are consistent, dump
+	 * our snapshot so others or we, after a restart, can use it.
+	 */
+	if (builder->state < SNAPBUILD_CONSISTENT)
+	{
+		/* returns false if there's no point in performing cleanup just yet */
+		if (!SnapBuildFindSnapshot(builder, lsn, running))
+			return;
+	}
+	else
+		SnapBuildSerialize(builder, lsn);
+
+	/*
+	 * Update range of interesting xids based on the running xacts
+	 * information. We don't increase ->xmax using it, because once we are in
+	 * a consistent state we can do that ourselves and much more efficiently
+	 * so, because we only need to do it for catalog transactions since we
+	 * only ever look at those.
+	 *
+	 * NB: We only increase xmax when a catalog modifying transaction commits
+	 * (see SnapBuildCommitTxn).  Because of this, xmax can be lower than
+	 * xmin, which looks odd but is correct and actually more efficient, since
+	 * we hit fast paths in heapam_visibility.c.
+	 */
+	builder->xmin = running->oldestRunningXid;
+
+	/* Remove transactions we don't need to keep track off anymore */
+	SnapBuildPurgeCommittedTxn(builder);
+
+	/*
+	 * Advance the xmin limit for the current replication slot, to allow
+	 * vacuum to clean up the tuples this slot has been protecting.
+	 *
+	 * The reorderbuffer might have an xmin among the currently running
+	 * snapshots; use it if so.  If not, we need only consider the snapshots
+	 * we'll produce later, which can't be less than the oldest running xid in
+	 * the record we're reading now.
+	 */
+	xmin = ReorderBufferGetOldestXmin(builder->reorder);
+	if (xmin == InvalidTransactionId)
+		xmin = running->oldestRunningXid;
+	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
+		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+	LogicalIncreaseXminForSlot(lsn, xmin);
+
+	/*
+	 * Also tell the slot where we can restart decoding from. We don't want to
+	 * do that after every commit because changing that implies an fsync of
+	 * the logical slot's state file, so we only do it every time we see a
+	 * running xacts record.
+	 *
+	 * Do so by looking for the oldest in progress transaction (determined by
+	 * the first LSN of any of its relevant records). Every transaction
+	 * remembers the last location we stored the snapshot to disk before its
+	 * beginning. That point is where we can restart from.
+	 */
+
+	/*
+	 * Can't know about a serialized snapshot's location if we're not
+	 * consistent.
+	 */
+	if (builder->state < SNAPBUILD_CONSISTENT)
+		return;
+
+	txn = ReorderBufferGetOldestTXN(builder->reorder);
+
+	/*
+	 * oldest ongoing txn might have started when we didn't yet serialize
+	 * anything because we hadn't reached a consistent state yet.
+	 */
+	if (txn != NULL && txn->restart_decoding_lsn != InvalidXLogRecPtr)
+		LogicalIncreaseRestartDecodingForSlot(lsn, txn->restart_decoding_lsn);
+
+	/*
+	 * No in-progress transaction, can reuse the last serialized snapshot if
+	 * we have one.
+	 */
+	else if (txn == NULL &&
+			 builder->reorder->current_restart_decoding_lsn != InvalidXLogRecPtr &&
+			 builder->last_serialized_snapshot != InvalidXLogRecPtr)
+		LogicalIncreaseRestartDecodingForSlot(lsn,
+											  builder->last_serialized_snapshot);
+}
+
+
+/*
+ * Build the start of a snapshot that's capable of decoding the catalog.
+ *
+ * Helper function for SnapBuildProcessRunningXacts() while we're not yet
+ * consistent.
+ *
+ * Returns true if there is a point in performing internal maintenance/cleanup
+ * using the xl_running_xacts record.
+ */
+static bool
+SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+{
+	/* ---
+	 * Build catalog decoding snapshot incrementally using information about
+	 * the currently running transactions. There are several ways to do that:
+	 *
+	 * a) There were no running transactions when the xl_running_xacts record
+	 *	  was inserted, jump to CONSISTENT immediately. We might find such a
+	 *	  state while waiting on c)'s sub-states.
+	 *
+	 * b) This (in a previous run) or another decoding slot serialized a
+	 *	  snapshot to disk that we can use.  Can't use this method for the
+	 *	  initial snapshot when slot is being created and needs full snapshot
+	 *	  for export or direct use, as that snapshot will only contain catalog
+	 *	  modifying transactions.
+	 *
+	 * c) First incrementally build a snapshot for catalog tuples
+	 *	  (BUILDING_SNAPSHOT), that requires all, already in-progress,
+	 *	  transactions to finish.  Every transaction starting after that
+	 *	  (FULL_SNAPSHOT state), has enough information to be decoded.  But
+	 *	  for older running transactions no viable snapshot exists yet, so
+	 *	  CONSISTENT will only be reached once all of those have finished.
+	 * ---
+	 */
+
+	/*
+	 * xl_running_xact record is older than what we can use, we might not have
+	 * all necessary catalog rows anymore.
+	 */
+	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
+		NormalTransactionIdPrecedes(running->oldestRunningXid,
+									builder->initial_xmin_horizon))
+	{
+		ereport(DEBUG1,
+				(errmsg_internal("skipping snapshot at %X/%X while building logical decoding snapshot, xmin horizon too low",
+								 LSN_FORMAT_ARGS(lsn)),
+				 errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
+									builder->initial_xmin_horizon, running->oldestRunningXid)));
+
+
+		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
+
+		return true;
+	}
+
+	/*
+	 * a) No transaction were running, we can jump to consistent.
+	 *
+	 * This is not affected by races around xl_running_xacts, because we can
+	 * miss transaction commits, but currently not transactions starting.
+	 *
+	 * NB: We might have already started to incrementally assemble a snapshot,
+	 * so we need to be careful to deal with that.
+	 */
+	if (running->oldestRunningXid == running->nextXid)
+	{
+		if (builder->start_decoding_at == InvalidXLogRecPtr ||
+			builder->start_decoding_at <= lsn)
+			/* can decode everything after this */
+			builder->start_decoding_at = lsn + 1;
+
+		/* As no transactions were running xmin/xmax can be trivially set. */
+		builder->xmin = running->nextXid;	/* < are finished */
+		builder->xmax = running->nextXid;	/* >= are running */
+
+		/* so we can safely use the faster comparisons */
+		Assert(TransactionIdIsNormal(builder->xmin));
+		Assert(TransactionIdIsNormal(builder->xmax));
+
+		builder->state = SNAPBUILD_CONSISTENT;
+		builder->next_phase_at = InvalidTransactionId;
+
+		ereport(LOG,
+				(errmsg("logical decoding found consistent point at %X/%X",
+						LSN_FORMAT_ARGS(lsn)),
+				 errdetail("There are no running transactions.")));
+
+		return false;
+	}
+	/* b) valid on disk state and not building full snapshot */
+	else if (!builder->building_full_snapshot &&
+			 SnapBuildRestore(builder, lsn))
+	{
+		/* there won't be any state to cleanup */
+		return false;
+	}
+
+	/*
+	 * c) transition from START to BUILDING_SNAPSHOT.
+	 *
+	 * In START state, and a xl_running_xacts record with running xacts is
+	 * encountered.  In that case, switch to BUILDING_SNAPSHOT state, and
+	 * record xl_running_xacts->nextXid.  Once all running xacts have finished
+	 * (i.e. they're all >= nextXid), we have a complete catalog snapshot.  It
+	 * might look that we could use xl_running_xact's ->xids information to
+	 * get there quicker, but that is problematic because transactions marked
+	 * as running, might already have inserted their commit record - it's
+	 * infeasible to change that with locking.
+	 */
+	else if (builder->state == SNAPBUILD_START)
+	{
+		builder->state = SNAPBUILD_BUILDING_SNAPSHOT;
+		builder->next_phase_at = running->nextXid;
+
+		/*
+		 * Start with an xmin/xmax that's correct for future, when all the
+		 * currently running transactions have finished. We'll update both
+		 * while waiting for the pending transactions to finish.
+		 */
+		builder->xmin = running->nextXid;	/* < are finished */
+		builder->xmax = running->nextXid;	/* >= are running */
+
+		/* so we can safely use the faster comparisons */
+		Assert(TransactionIdIsNormal(builder->xmin));
+		Assert(TransactionIdIsNormal(builder->xmax));
+
+		ereport(LOG,
+				(errmsg("logical decoding found initial starting point at %X/%X",
+						LSN_FORMAT_ARGS(lsn)),
+				 errdetail("Waiting for transactions (approximately %d) older than %u to end.",
+						   running->xcnt, running->nextXid)));
+
+		SnapBuildWaitSnapshot(running, running->nextXid);
+	}
+
+	/*
+	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
+	 *
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
+	 * means all transactions starting afterwards have enough information to
+	 * be decoded.  Switch to FULL_SNAPSHOT.
+	 */
+	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
+			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
+										   running->oldestRunningXid))
+	{
+		builder->state = SNAPBUILD_FULL_SNAPSHOT;
+		builder->next_phase_at = running->nextXid;
+
+		ereport(LOG,
+				(errmsg("logical decoding found initial consistent point at %X/%X",
+						LSN_FORMAT_ARGS(lsn)),
+				 errdetail("Waiting for transactions (approximately %d) older than %u to end.",
+						   running->xcnt, running->nextXid)));
+
+		SnapBuildWaitSnapshot(running, running->nextXid);
+	}
+
+	/*
+	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
+	 *
+	 * In FULL_SNAPSHOT state (see d) ), and this xl_running_xacts'
+	 * oldestRunningXid is >= than nextXid from when we switched to
+	 * FULL_SNAPSHOT.  This means all transactions that are currently in
+	 * progress have a catalog snapshot, and all their changes have been
+	 * collected.  Switch to CONSISTENT.
+	 */
+	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
+			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
+										   running->oldestRunningXid))
+	{
+		builder->state = SNAPBUILD_CONSISTENT;
+		builder->next_phase_at = InvalidTransactionId;
+
+		ereport(LOG,
+				(errmsg("logical decoding found consistent point at %X/%X",
+						LSN_FORMAT_ARGS(lsn)),
+				 errdetail("There are no old transactions anymore.")));
+	}
+
+	/*
+	 * We already started to track running xacts and need to wait for all
+	 * in-progress ones to finish. We fall through to the normal processing of
+	 * records so incremental cleanup can be performed.
+	 */
+	return true;
+
+}
+
+/* ---
+ * Iterate through xids in record, wait for all older than the cutoff to
+ * finish.  Then, if possible, log a new xl_running_xacts record.
+ *
+ * This isn't required for the correctness of decoding, but to:
+ * a) allow isolationtester to notice that we're currently waiting for
+ *	  something.
+ * b) log a new xl_running_xacts record where it'd be helpful, without having
+ *	  to wait for bgwriter or checkpointer.
+ * ---
+ */
+static void
+SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
+{
+	int			off;
+
+	for (off = 0; off < running->xcnt; off++)
+	{
+		TransactionId xid = running->xids[off];
+
+		/*
+		 * Upper layers should prevent that we ever need to wait on ourselves.
+		 * Check anyway, since failing to do so would either result in an
+		 * endless wait or an Assert() failure.
+		 */
+		if (TransactionIdIsCurrentTransactionId(xid))
+			elog(ERROR, "waiting for ourselves");
+
+		if (TransactionIdFollows(xid, cutoff))
+			continue;
+
+		XactLockTableWait(xid, NULL, NULL, XLTW_None);
+	}
+
+	/*
+	 * All transactions we needed to finish finished - try to ensure there is
+	 * another xl_running_xacts record in a timely manner, without having to
+	 * wait for bgwriter or checkpointer to log one.  During recovery we can't
+	 * enforce that, so we'll have to wait.
+	 */
+	if (!RecoveryInProgress())
+	{
+		LogStandbySnapshot();
+	}
+}
+
+/* -----------------------------------
+ * Snapshot serialization support
+ * -----------------------------------
+ */
+
+/*
+ * We store current state of struct SnapBuild on disk in the following manner:
+ *
+ * struct SnapBuildOnDisk;
+ * TransactionId * running.xcnt_space;
+ * TransactionId * committed.xcnt; (*not xcnt_space*)
+ *
+ */
+typedef struct SnapBuildOnDisk
+{
+	/* first part of this struct needs to be version independent */
+
+	/* data not covered by checksum */
+	uint32		magic;
+	pg_crc32c	checksum;
+
+	/* data covered by checksum */
+
+	/* version, in case we want to support pg_upgrade */
+	uint32		version;
+	/* how large is the on disk data, excluding the constant sized part */
+	uint32		length;
+
+	/* version dependent part */
+	SnapBuild	builder;
+
+	/* variable amount of TransactionIds follows */
+} SnapBuildOnDisk;
+
+#define SnapBuildOnDiskConstantSize \
+	offsetof(SnapBuildOnDisk, builder)
+#define SnapBuildOnDiskNotChecksummedSize \
+	offsetof(SnapBuildOnDisk, version)
+
+#define SNAPBUILD_MAGIC 0x51A1E001
+#define SNAPBUILD_VERSION 4
+
+/*
+ * Store/Load a snapshot from disk, depending on the snapshot builder's state.
+ *
+ * Supposed to be used by external (i.e. not snapbuild.c) code that just read
+ * a record that's a potential location for a serialized snapshot.
+ */
+void
+SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn)
+{
+	if (builder->state < SNAPBUILD_CONSISTENT)
+		SnapBuildRestore(builder, lsn);
+	else
+		SnapBuildSerialize(builder, lsn);
+}
+
+/*
+ * Serialize the snapshot 'builder' at the location 'lsn' if it hasn't already
+ * been done by another decoding process.
+ */
+static void
+SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
+{
+	Size		needed_length;
+	SnapBuildOnDisk *ondisk = NULL;
+	char	   *ondisk_c;
+	int			fd;
+	char		tmppath[MAXPGPATH];
+	char		path[MAXPGPATH];
+	int			ret;
+	struct stat stat_buf;
+	Size		sz;
+
+	Assert(lsn != InvalidXLogRecPtr);
+	Assert(builder->last_serialized_snapshot == InvalidXLogRecPtr ||
+		   builder->last_serialized_snapshot <= lsn);
+
+	/*
+	 * no point in serializing if we cannot continue to work immediately after
+	 * restoring the snapshot
+	 */
+	if (builder->state < SNAPBUILD_CONSISTENT)
+		return;
+
+	/* consistent snapshots have no next phase */
+	Assert(builder->next_phase_at == InvalidTransactionId);
+
+	/*
+	 * We identify snapshots by the LSN they are valid for. We don't need to
+	 * include timelines in the name as each LSN maps to exactly one timeline
+	 * unless the user used pg_resetwal or similar. If a user did so, there's
+	 * no hope continuing to decode anyway.
+	 */
+	sprintf(path, "pg_logical/snapshots/%X-%X.snap",
+			LSN_FORMAT_ARGS(lsn));
+
+	/*
+	 * first check whether some other backend already has written the snapshot
+	 * for this LSN. It's perfectly fine if there's none, so we accept ENOENT
+	 * as a valid state. Everything else is an unexpected error.
+	 */
+	ret = stat(path, &stat_buf);
+
+	if (ret != 0 && errno != ENOENT)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not stat file \"%s\": %m", path)));
+
+	else if (ret == 0)
+	{
+		/*
+		 * somebody else has already serialized to this point, don't overwrite
+		 * but remember location, so we don't need to read old data again.
+		 *
+		 * To be sure it has been synced to disk after the rename() from the
+		 * tempfile filename to the real filename, we just repeat the fsync.
+		 * That ought to be cheap because in most scenarios it should already
+		 * be safely on disk.
+		 */
+		fsync_fname(path, false);
+		fsync_fname("pg_logical/snapshots", true);
+
+		builder->last_serialized_snapshot = lsn;
+		goto out;
+	}
+
+	/*
+	 * there is an obvious race condition here between the time we stat(2) the
+	 * file and us writing the file. But we rename the file into place
+	 * atomically and all files created need to contain the same data anyway,
+	 * so this is perfectly fine, although a bit of a resource waste. Locking
+	 * seems like pointless complication.
+	 */
+	elog(DEBUG1, "serializing snapshot to %s", path);
+
+	/* to make sure only we will write to this tempfile, include pid */
+	sprintf(tmppath, "pg_logical/snapshots/%X-%X.snap.%d.tmp",
+			LSN_FORMAT_ARGS(lsn), MyProcPid);
+
+	/*
+	 * Unlink temporary file if it already exists, needs to have been before a
+	 * crash/error since we won't enter this function twice from within a
+	 * single decoding slot/backend and the temporary file contains the pid of
+	 * the current process.
+	 */
+	if (unlink(tmppath) != 0 && errno != ENOENT)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not remove file \"%s\": %m", tmppath)));
+
+	needed_length = sizeof(SnapBuildOnDisk) +
+		sizeof(TransactionId) * builder->committed.xcnt;
+
+	ondisk_c = MemoryContextAllocZero(builder->context, needed_length);
+	ondisk = (SnapBuildOnDisk *) ondisk_c;
+	ondisk->magic = SNAPBUILD_MAGIC;
+	ondisk->version = SNAPBUILD_VERSION;
+	ondisk->length = needed_length;
+	INIT_CRC32C(ondisk->checksum);
+	COMP_CRC32C(ondisk->checksum,
+				((char *) ondisk) + SnapBuildOnDiskNotChecksummedSize,
+				SnapBuildOnDiskConstantSize - SnapBuildOnDiskNotChecksummedSize);
+	ondisk_c += sizeof(SnapBuildOnDisk);
+
+	memcpy(&ondisk->builder, builder, sizeof(SnapBuild));
+	/* NULL-ify memory-only data */
+	ondisk->builder.context = NULL;
+	ondisk->builder.snapshot = NULL;
+	ondisk->builder.reorder = NULL;
+	ondisk->builder.committed.xip = NULL;
+
+	COMP_CRC32C(ondisk->checksum,
+				&ondisk->builder,
+				sizeof(SnapBuild));
+
+	/* copy committed xacts */
+	sz = sizeof(TransactionId) * builder->committed.xcnt;
+	memcpy(ondisk_c, builder->committed.xip, sz);
+	COMP_CRC32C(ondisk->checksum, ondisk_c, sz);
+	ondisk_c += sz;
+
+	FIN_CRC32C(ondisk->checksum);
+
+	/* we have valid data now, open tempfile and write it there */
+	fd = OpenTransientFile(tmppath,
+						   O_CREAT | O_EXCL | O_WRONLY | PG_BINARY);
+	if (fd < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not open file \"%s\": %m", tmppath)));
+
+	errno = 0;
+	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_WRITE);
+	if ((write(fd, ondisk, needed_length)) != needed_length)
+	{
+		int			save_errno = errno;
+
+		CloseTransientFile(fd);
+
+		/* if write didn't set errno, assume problem is no disk space */
+		errno = save_errno ? save_errno : ENOSPC;
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not write to file \"%s\": %m", tmppath)));
+	}
+	pgstat_report_wait_end();
+
+	/*
+	 * fsync the file before renaming so that even if we crash after this we
+	 * have either a fully valid file or nothing.
+	 *
+	 * It's safe to just ERROR on fsync() here because we'll retry the whole
+	 * operation including the writes.
+	 *
+	 * TODO: Do the fsync() via checkpoints/restartpoints, doing it here has
+	 * some noticeable overhead since it's performed synchronously during
+	 * decoding?
+	 */
+	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_SYNC);
+	if (pg_fsync(fd) != 0)
+	{
+		int			save_errno = errno;
+
+		CloseTransientFile(fd);
+		errno = save_errno;
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not fsync file \"%s\": %m", tmppath)));
+	}
+	pgstat_report_wait_end();
+
+	if (CloseTransientFile(fd) != 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m", tmppath)));
+
+	fsync_fname("pg_logical/snapshots", true);
+
+	/*
+	 * We may overwrite the work from some other backend, but that's ok, our
+	 * snapshot is valid as well, we'll just have done some superfluous work.
+	 */
+	if (rename(tmppath, path) != 0)
+	{
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not rename file \"%s\" to \"%s\": %m",
+						tmppath, path)));
+	}
+
+	/* make sure we persist */
+	fsync_fname(path, false);
+	fsync_fname("pg_logical/snapshots", true);
+
+	/*
+	 * Now there's no way we can loose the dumped state anymore, remember this
+	 * as a serialization point.
+	 */
+	builder->last_serialized_snapshot = lsn;
+
+out:
+	ReorderBufferSetRestartPoint(builder->reorder,
+								 builder->last_serialized_snapshot);
+	/* be tidy */
+	if (ondisk)
+		pfree(ondisk);
+}
+
+/*
+ * Restore a snapshot into 'builder' if previously one has been stored at the
+ * location indicated by 'lsn'. Returns true if successful, false otherwise.
+ */
+static bool
+SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
+{
+	SnapBuildOnDisk ondisk;
+	int			fd;
+	char		path[MAXPGPATH];
+	Size		sz;
+	int			readBytes;
+	pg_crc32c	checksum;
+
+	/* no point in loading a snapshot if we're already there */
+	if (builder->state == SNAPBUILD_CONSISTENT)
+		return false;
+
+	sprintf(path, "pg_logical/snapshots/%X-%X.snap",
+			LSN_FORMAT_ARGS(lsn));
+
+	fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
+
+	if (fd < 0 && errno == ENOENT)
+		return false;
+	else if (fd < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not open file \"%s\": %m", path)));
+
+	/* ----
+	 * Make sure the snapshot had been stored safely to disk, that's normally
+	 * cheap.
+	 * Note that we do not need PANIC here, nobody will be able to use the
+	 * slot without fsyncing, and saving it won't succeed without an fsync()
+	 * either...
+	 * ----
+	 */
+	fsync_fname(path, false);
+	fsync_fname("pg_logical/snapshots", true);
+
+
+	/* read statically sized portion of snapshot */
+	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
+	readBytes = read(fd, &ondisk, SnapBuildOnDiskConstantSize);
+	pgstat_report_wait_end();
+	if (readBytes != SnapBuildOnDiskConstantSize)
+	{
+		int			save_errno = errno;
+
+		CloseTransientFile(fd);
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_DATA_CORRUPTED),
+					 errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes,
+							(Size) SnapBuildOnDiskConstantSize)));
+	}
+
+	if (ondisk.magic != SNAPBUILD_MAGIC)
+		ereport(ERROR,
+				(errcode(ERRCODE_DATA_CORRUPTED),
+				 errmsg("snapbuild state file \"%s\" has wrong magic number: %u instead of %u",
+						path, ondisk.magic, SNAPBUILD_MAGIC)));
+
+	if (ondisk.version != SNAPBUILD_VERSION)
+		ereport(ERROR,
+				(errcode(ERRCODE_DATA_CORRUPTED),
+				 errmsg("snapbuild state file \"%s\" has unsupported version: %u instead of %u",
+						path, ondisk.version, SNAPBUILD_VERSION)));
+
+	INIT_CRC32C(checksum);
+	COMP_CRC32C(checksum,
+				((char *) &ondisk) + SnapBuildOnDiskNotChecksummedSize,
+				SnapBuildOnDiskConstantSize - SnapBuildOnDiskNotChecksummedSize);
+
+	/* read SnapBuild */
+	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
+	readBytes = read(fd, &ondisk.builder, sizeof(SnapBuild));
+	pgstat_report_wait_end();
+	if (readBytes != sizeof(SnapBuild))
+	{
+		int			save_errno = errno;
+
+		CloseTransientFile(fd);
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_DATA_CORRUPTED),
+					 errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sizeof(SnapBuild))));
+	}
+	COMP_CRC32C(checksum, &ondisk.builder, sizeof(SnapBuild));
+
+	/* restore committed xacts information */
+	sz = sizeof(TransactionId) * ondisk.builder.committed.xcnt;
+	ondisk.builder.committed.xip = MemoryContextAllocZero(builder->context, sz);
+	pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
+	readBytes = read(fd, ondisk.builder.committed.xip, sz);
+	pgstat_report_wait_end();
+	if (readBytes != sz)
+	{
+		int			save_errno = errno;
+
+		CloseTransientFile(fd);
+
+		if (readBytes < 0)
+		{
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m", path)));
+		}
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_DATA_CORRUPTED),
+					 errmsg("could not read file \"%s\": read %d of %zu",
+							path, readBytes, sz)));
+	}
+	COMP_CRC32C(checksum, ondisk.builder.committed.xip, sz);
+
+	if (CloseTransientFile(fd) != 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m", path)));
+
+	FIN_CRC32C(checksum);
+
+	/* verify checksum of what we've read */
+	if (!EQ_CRC32C(checksum, ondisk.checksum))
+		ereport(ERROR,
+				(errcode(ERRCODE_DATA_CORRUPTED),
+				 errmsg("checksum mismatch for snapbuild state file \"%s\": is %u, should be %u",
+						path, checksum, ondisk.checksum)));
+
+	/*
+	 * ok, we now have a sensible snapshot here, figure out if it has more
+	 * information than we have.
+	 */
+
+	/*
+	 * We are only interested in consistent snapshots for now, comparing
+	 * whether one incomplete snapshot is more "advanced" seems to be
+	 * unnecessarily complex.
+	 */
+	if (ondisk.builder.state < SNAPBUILD_CONSISTENT)
+		goto snapshot_not_interesting;
+
+	/*
+	 * Don't use a snapshot that requires an xmin that we cannot guarantee to
+	 * be available.
+	 */
+	if (TransactionIdPrecedes(ondisk.builder.xmin, builder->initial_xmin_horizon))
+		goto snapshot_not_interesting;
+
+	/* consistent snapshots have no next phase */
+	Assert(ondisk.builder.next_phase_at == InvalidTransactionId);
+
+	/* ok, we think the snapshot is sensible, copy over everything important */
+	builder->xmin = ondisk.builder.xmin;
+	builder->xmax = ondisk.builder.xmax;
+	builder->state = ondisk.builder.state;
+
+	builder->committed.xcnt = ondisk.builder.committed.xcnt;
+	/* We only allocated/stored xcnt, not xcnt_space xids ! */
+	/* don't overwrite preallocated xip, if we don't have anything here */
+	if (builder->committed.xcnt > 0)
+	{
+		pfree(builder->committed.xip);
+		builder->committed.xcnt_space = ondisk.builder.committed.xcnt;
+		builder->committed.xip = ondisk.builder.committed.xip;
+	}
+	ondisk.builder.committed.xip = NULL;
+
+	/* our snapshot is not interesting anymore, build a new one */
+	if (builder->snapshot != NULL)
+	{
+		SnapBuildSnapDecRefcount(builder->snapshot);
+	}
+	builder->snapshot = SnapBuildBuildSnapshot(builder);
+	SnapBuildSnapIncRefcount(builder->snapshot);
+
+	ReorderBufferSetRestartPoint(builder->reorder, lsn);
+
+	Assert(builder->state == SNAPBUILD_CONSISTENT);
+
+	ereport(LOG,
+			(errmsg("logical decoding found consistent point at %X/%X",
+					LSN_FORMAT_ARGS(lsn)),
+			 errdetail("Logical decoding will begin using saved snapshot.")));
+	return true;
+
+snapshot_not_interesting:
+	if (ondisk.builder.committed.xip != NULL)
+		pfree(ondisk.builder.committed.xip);
+	return false;
+}
+
+/*
+ * Remove all serialized snapshots that are not required anymore because no
+ * slot can need them. This doesn't actually have to run during a checkpoint,
+ * but it's a convenient point to schedule this.
+ *
+ * NB: We run this during checkpoints even if logical decoding is disabled so
+ * we cleanup old slots at some point after it got disabled.
+ */
+void
+CheckPointSnapBuild(void)
+{
+	XLogRecPtr	cutoff;
+	XLogRecPtr	redo;
+	DIR		   *snap_dir;
+	struct dirent *snap_de;
+	char		path[MAXPGPATH + 21];
+
+	/*
+	 * We start off with a minimum of the last redo pointer. No new
+	 * replication slot will start before that, so that's a safe upper bound
+	 * for removal.
+	 */
+	redo = GetRedoRecPtr();
+
+	/* now check for the restart ptrs from existing slots */
+	cutoff = ReplicationSlotsComputeLogicalRestartLSN();
+
+	/* don't start earlier than the restart lsn */
+	if (redo < cutoff)
+		cutoff = redo;
+
+	snap_dir = AllocateDir("pg_logical/snapshots");
+	while ((snap_de = ReadDir(snap_dir, "pg_logical/snapshots")) != NULL)
+	{
+		uint32		hi;
+		uint32		lo;
+		XLogRecPtr	lsn;
+		struct stat statbuf;
+
+		if (strcmp(snap_de->d_name, ".") == 0 ||
+			strcmp(snap_de->d_name, "..") == 0)
+			continue;
+
+		snprintf(path, sizeof(path), "pg_logical/snapshots/%s", snap_de->d_name);
+
+		if (lstat(path, &statbuf) == 0 && !S_ISREG(statbuf.st_mode))
+		{
+			elog(DEBUG1, "only regular files expected: %s", path);
+			continue;
+		}
+
+		/*
+		 * temporary filenames from SnapBuildSerialize() include the LSN and
+		 * everything but are postfixed by .$pid.tmp. We can just remove them
+		 * the same as other files because there can be none that are
+		 * currently being written that are older than cutoff.
+		 *
+		 * We just log a message if a file doesn't fit the pattern, it's
+		 * probably some editors lock/state file or similar...
+		 */
+		if (sscanf(snap_de->d_name, "%X-%X.snap", &hi, &lo) != 2)
+		{
+			ereport(LOG,
+					(errmsg("could not parse file name \"%s\"", path)));
+			continue;
+		}
+
+		lsn = ((uint64) hi) << 32 | lo;
+
+		/* check whether we still need it */
+		if (lsn < cutoff || cutoff == InvalidXLogRecPtr)
+		{
+			elog(DEBUG1, "removing snapbuild snapshot %s", path);
+
+			/*
+			 * It's not particularly harmful, though strange, if we can't
+			 * remove the file here. Don't prevent the checkpoint from
+			 * completing, that'd be a cure worse than the disease.
+			 */
+			if (unlink(path) < 0)
+			{
+				ereport(LOG,
+						(errcode_for_file_access(),
+						 errmsg("could not remove file \"%s\": %m",
+								path)));
+				continue;
+			}
+		}
+	}
+	FreeDir(snap_dir);
+}
diff --git a/src/backend/replication/logical/tablesync.c b/src/backend/replication/logical/tablesync.c
new file mode 100644
index 0000000..682c107
--- /dev/null
+++ b/src/backend/replication/logical/tablesync.c
@@ -0,0 +1,1160 @@
+/*-------------------------------------------------------------------------
+ * tablesync.c
+ *	  PostgreSQL logical replication: initial table data synchronization
+ *
+ * Copyright (c) 2012-2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/tablesync.c
+ *
+ * NOTES
+ *	  This file contains code for initial table data synchronization for
+ *	  logical replication.
+ *
+ *	  The initial data synchronization is done separately for each table,
+ *	  in a separate apply worker that only fetches the initial snapshot data
+ *	  from the publisher and then synchronizes the position in the stream with
+ *	  the main apply worker.
+ *
+ *	  There are several reasons for doing the synchronization this way:
+ *	   - It allows us to parallelize the initial data synchronization
+ *		 which lowers the time needed for it to happen.
+ *	   - The initial synchronization does not have to hold the xid and LSN
+ *		 for the time it takes to copy data of all tables, causing less
+ *		 bloat and lower disk consumption compared to doing the
+ *		 synchronization in a single process for the whole database.
+ *	   - It allows us to synchronize any tables added after the initial
+ *		 synchronization has finished.
+ *
+ *	  The stream position synchronization works in multiple steps:
+ *	   - Apply worker requests a tablesync worker to start, setting the new
+ *		 table state to INIT.
+ *	   - Tablesync worker starts; changes table state from INIT to DATASYNC while
+ *		 copying.
+ *	   - Tablesync worker does initial table copy; there is a FINISHEDCOPY (sync
+ *		 worker specific) state to indicate when the copy phase has completed, so
+ *		 if the worker crashes with this (non-memory) state then the copy will not
+ *		 be re-attempted.
+ *	   - Tablesync worker then sets table state to SYNCWAIT; waits for state change.
+ *	   - Apply worker periodically checks for tables in SYNCWAIT state.  When
+ *		 any appear, it sets the table state to CATCHUP and starts loop-waiting
+ *		 until either the table state is set to SYNCDONE or the sync worker
+ *		 exits.
+ *	   - After the sync worker has seen the state change to CATCHUP, it will
+ *		 read the stream and apply changes (acting like an apply worker) until
+ *		 it catches up to the specified stream position.  Then it sets the
+ *		 state to SYNCDONE.  There might be zero changes applied between
+ *		 CATCHUP and SYNCDONE, because the sync worker might be ahead of the
+ *		 apply worker.
+ *	   - Once the state is set to SYNCDONE, the apply will continue tracking
+ *		 the table until it reaches the SYNCDONE stream position, at which
+ *		 point it sets state to READY and stops tracking.  Again, there might
+ *		 be zero changes in between.
+ *
+ *	  So the state progression is always: INIT -> DATASYNC -> FINISHEDCOPY
+ *	  -> SYNCWAIT -> CATCHUP -> SYNCDONE -> READY.
+ *
+ *	  The catalog pg_subscription_rel is used to keep information about
+ *	  subscribed tables and their state.  The catalog holds all states
+ *	  except SYNCWAIT and CATCHUP which are only in shared memory.
+ *
+ *	  Example flows look like this:
+ *	   - Apply is in front:
+ *		  sync:8
+ *			-> set in catalog FINISHEDCOPY
+ *			-> set in memory SYNCWAIT
+ *		  apply:10
+ *			-> set in memory CATCHUP
+ *			-> enter wait-loop
+ *		  sync:10
+ *			-> set in catalog SYNCDONE
+ *			-> exit
+ *		  apply:10
+ *			-> exit wait-loop
+ *			-> continue rep
+ *		  apply:11
+ *			-> set in catalog READY
+ *
+ *	   - Sync is in front:
+ *		  sync:10
+ *			-> set in catalog FINISHEDCOPY
+ *			-> set in memory SYNCWAIT
+ *		  apply:8
+ *			-> set in memory CATCHUP
+ *			-> continue per-table filtering
+ *		  sync:10
+ *			-> set in catalog SYNCDONE
+ *			-> exit
+ *		  apply:10
+ *			-> set in catalog READY
+ *			-> stop per-table filtering
+ *			-> continue rep
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/table.h"
+#include "access/xact.h"
+#include "catalog/pg_subscription_rel.h"
+#include "catalog/pg_type.h"
+#include "commands/copy.h"
+#include "miscadmin.h"
+#include "parser/parse_relation.h"
+#include "pgstat.h"
+#include "replication/logicallauncher.h"
+#include "replication/logicalrelation.h"
+#include "replication/walreceiver.h"
+#include "replication/worker_internal.h"
+#include "replication/slot.h"
+#include "replication/origin.h"
+#include "storage/ipc.h"
+#include "storage/lmgr.h"
+#include "utils/builtins.h"
+#include "utils/lsyscache.h"
+#include "utils/memutils.h"
+#include "utils/snapmgr.h"
+
+static bool table_states_valid = false;
+
+StringInfo	copybuf = NULL;
+
+/*
+ * Exit routine for synchronization worker.
+ */
+static void
+pg_attribute_noreturn()
+finish_sync_worker(void)
+{
+	/*
+	 * Commit any outstanding transaction. This is the usual case, unless
+	 * there was nothing to do for the table.
+	 */
+	if (IsTransactionState())
+	{
+		CommitTransactionCommand();
+		pgstat_report_stat(false);
+	}
+
+	/* And flush all writes. */
+	XLogFlush(GetXLogWriteRecPtr());
+
+	StartTransactionCommand();
+	ereport(LOG,
+			(errmsg("logical replication table synchronization worker for subscription \"%s\", table \"%s\" has finished",
+					MySubscription->name,
+					get_rel_name(MyLogicalRepWorker->relid))));
+	CommitTransactionCommand();
+
+	/* Find the main apply worker and signal it. */
+	logicalrep_worker_wakeup(MyLogicalRepWorker->subid, InvalidOid);
+
+	/* Stop gracefully */
+	proc_exit(0);
+}
+
+/*
+ * Wait until the relation sync state is set in the catalog to the expected
+ * one; return true when it happens.
+ *
+ * Returns false if the table sync worker or the table itself have
+ * disappeared, or the table state has been reset.
+ *
+ * Currently, this is used in the apply worker when transitioning from
+ * CATCHUP state to SYNCDONE.
+ */
+static bool
+wait_for_relation_state_change(Oid relid, char expected_state)
+{
+	char		state;
+
+	for (;;)
+	{
+		LogicalRepWorker *worker;
+		XLogRecPtr	statelsn;
+
+		CHECK_FOR_INTERRUPTS();
+
+		InvalidateCatalogSnapshot();
+		state = GetSubscriptionRelState(MyLogicalRepWorker->subid,
+										relid, &statelsn);
+
+		if (state == SUBREL_STATE_UNKNOWN)
+			break;
+
+		if (state == expected_state)
+			return true;
+
+		/* Check if the sync worker is still running and bail if not. */
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+		worker = logicalrep_worker_find(MyLogicalRepWorker->subid, relid,
+										false);
+		LWLockRelease(LogicalRepWorkerLock);
+		if (!worker)
+			break;
+
+		(void) WaitLatch(MyLatch,
+						 WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+						 1000L, WAIT_EVENT_LOGICAL_SYNC_STATE_CHANGE);
+
+		ResetLatch(MyLatch);
+	}
+
+	return false;
+}
+
+/*
+ * Wait until the apply worker changes the state of our synchronization
+ * worker to the expected one.
+ *
+ * Used when transitioning from SYNCWAIT state to CATCHUP.
+ *
+ * Returns false if the apply worker has disappeared.
+ */
+static bool
+wait_for_worker_state_change(char expected_state)
+{
+	int			rc;
+
+	for (;;)
+	{
+		LogicalRepWorker *worker;
+
+		CHECK_FOR_INTERRUPTS();
+
+		/*
+		 * Done if already in correct state.  (We assume this fetch is atomic
+		 * enough to not give a misleading answer if we do it with no lock.)
+		 */
+		if (MyLogicalRepWorker->relstate == expected_state)
+			return true;
+
+		/*
+		 * Bail out if the apply worker has died, else signal it we're
+		 * waiting.
+		 */
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+		worker = logicalrep_worker_find(MyLogicalRepWorker->subid,
+										InvalidOid, false);
+		if (worker && worker->proc)
+			logicalrep_worker_wakeup_ptr(worker);
+		LWLockRelease(LogicalRepWorkerLock);
+		if (!worker)
+			break;
+
+		/*
+		 * Wait.  We expect to get a latch signal back from the apply worker,
+		 * but use a timeout in case it dies without sending one.
+		 */
+		rc = WaitLatch(MyLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+					   1000L, WAIT_EVENT_LOGICAL_SYNC_STATE_CHANGE);
+
+		if (rc & WL_LATCH_SET)
+			ResetLatch(MyLatch);
+	}
+
+	return false;
+}
+
+/*
+ * Callback from syscache invalidation.
+ */
+void
+invalidate_syncing_table_states(Datum arg, int cacheid, uint32 hashvalue)
+{
+	table_states_valid = false;
+}
+
+/*
+ * Handle table synchronization cooperation from the synchronization
+ * worker.
+ *
+ * If the sync worker is in CATCHUP state and reached (or passed) the
+ * predetermined synchronization point in the WAL stream, mark the table as
+ * SYNCDONE and finish.
+ */
+static void
+process_syncing_tables_for_sync(XLogRecPtr current_lsn)
+{
+	SpinLockAcquire(&MyLogicalRepWorker->relmutex);
+
+	if (MyLogicalRepWorker->relstate == SUBREL_STATE_CATCHUP &&
+		current_lsn >= MyLogicalRepWorker->relstate_lsn)
+	{
+		TimeLineID	tli;
+		char		syncslotname[NAMEDATALEN] = {0};
+
+		MyLogicalRepWorker->relstate = SUBREL_STATE_SYNCDONE;
+		MyLogicalRepWorker->relstate_lsn = current_lsn;
+
+		SpinLockRelease(&MyLogicalRepWorker->relmutex);
+
+		/*
+		 * UpdateSubscriptionRelState must be called within a transaction.
+		 * That transaction will be ended within the finish_sync_worker().
+		 */
+		if (!IsTransactionState())
+			StartTransactionCommand();
+
+		UpdateSubscriptionRelState(MyLogicalRepWorker->subid,
+								   MyLogicalRepWorker->relid,
+								   MyLogicalRepWorker->relstate,
+								   MyLogicalRepWorker->relstate_lsn);
+
+		/*
+		 * End streaming so that LogRepWorkerWalRcvConn can be used to drop
+		 * the slot.
+		 */
+		walrcv_endstreaming(LogRepWorkerWalRcvConn, &tli);
+
+		/*
+		 * Cleanup the tablesync slot.
+		 *
+		 * This has to be done after updating the state because otherwise if
+		 * there is an error while doing the database operations we won't be
+		 * able to rollback dropped slot.
+		 */
+		ReplicationSlotNameForTablesync(MyLogicalRepWorker->subid,
+										MyLogicalRepWorker->relid,
+										syncslotname,
+										sizeof(syncslotname));
+
+		/*
+		 * It is important to give an error if we are unable to drop the slot,
+		 * otherwise, it won't be dropped till the corresponding subscription
+		 * is dropped. So passing missing_ok = false.
+		 */
+		ReplicationSlotDropAtPubNode(LogRepWorkerWalRcvConn, syncslotname, false);
+
+		finish_sync_worker();
+	}
+	else
+		SpinLockRelease(&MyLogicalRepWorker->relmutex);
+}
+
+/*
+ * Handle table synchronization cooperation from the apply worker.
+ *
+ * Walk over all subscription tables that are individually tracked by the
+ * apply process (currently, all that have state other than
+ * SUBREL_STATE_READY) and manage synchronization for them.
+ *
+ * If there are tables that need synchronizing and are not being synchronized
+ * yet, start sync workers for them (if there are free slots for sync
+ * workers).  To prevent starting the sync worker for the same relation at a
+ * high frequency after a failure, we store its last start time with each sync
+ * state info.  We start the sync worker for the same relation after waiting
+ * at least wal_retrieve_retry_interval.
+ *
+ * For tables that are being synchronized already, check if sync workers
+ * either need action from the apply worker or have finished.  This is the
+ * SYNCWAIT to CATCHUP transition.
+ *
+ * If the synchronization position is reached (SYNCDONE), then the table can
+ * be marked as READY and is no longer tracked.
+ */
+static void
+process_syncing_tables_for_apply(XLogRecPtr current_lsn)
+{
+	struct tablesync_start_time_mapping
+	{
+		Oid			relid;
+		TimestampTz last_start_time;
+	};
+	static List *table_states = NIL;
+	static HTAB *last_start_times = NULL;
+	ListCell   *lc;
+	bool		started_tx = false;
+
+	Assert(!IsTransactionState());
+
+	/* We need up-to-date sync state info for subscription tables here. */
+	if (!table_states_valid)
+	{
+		MemoryContext oldctx;
+		List	   *rstates;
+		ListCell   *lc;
+		SubscriptionRelState *rstate;
+
+		/* Clean the old list. */
+		list_free_deep(table_states);
+		table_states = NIL;
+
+		StartTransactionCommand();
+		started_tx = true;
+
+		/* Fetch all non-ready tables. */
+		rstates = GetSubscriptionNotReadyRelations(MySubscription->oid);
+
+		/* Allocate the tracking info in a permanent memory context. */
+		oldctx = MemoryContextSwitchTo(CacheMemoryContext);
+		foreach(lc, rstates)
+		{
+			rstate = palloc(sizeof(SubscriptionRelState));
+			memcpy(rstate, lfirst(lc), sizeof(SubscriptionRelState));
+			table_states = lappend(table_states, rstate);
+		}
+		MemoryContextSwitchTo(oldctx);
+
+		table_states_valid = true;
+	}
+
+	/*
+	 * Prepare a hash table for tracking last start times of workers, to avoid
+	 * immediate restarts.  We don't need it if there are no tables that need
+	 * syncing.
+	 */
+	if (table_states && !last_start_times)
+	{
+		HASHCTL		ctl;
+
+		ctl.keysize = sizeof(Oid);
+		ctl.entrysize = sizeof(struct tablesync_start_time_mapping);
+		last_start_times = hash_create("Logical replication table sync worker start times",
+									   256, &ctl, HASH_ELEM | HASH_BLOBS);
+	}
+
+	/*
+	 * Clean up the hash table when we're done with all tables (just to
+	 * release the bit of memory).
+	 */
+	else if (!table_states && last_start_times)
+	{
+		hash_destroy(last_start_times);
+		last_start_times = NULL;
+	}
+
+	/*
+	 * Process all tables that are being synchronized.
+	 */
+	foreach(lc, table_states)
+	{
+		SubscriptionRelState *rstate = (SubscriptionRelState *) lfirst(lc);
+
+		if (rstate->state == SUBREL_STATE_SYNCDONE)
+		{
+			/*
+			 * Apply has caught up to the position where the table sync has
+			 * finished.  Mark the table as ready so that the apply will just
+			 * continue to replicate it normally.
+			 */
+			if (current_lsn >= rstate->lsn)
+			{
+				char		originname[NAMEDATALEN];
+
+				rstate->state = SUBREL_STATE_READY;
+				rstate->lsn = current_lsn;
+				if (!started_tx)
+				{
+					StartTransactionCommand();
+					started_tx = true;
+				}
+
+				/*
+				 * Remove the tablesync origin tracking if exists.
+				 *
+				 * The normal case origin drop is done here instead of in the
+				 * process_syncing_tables_for_sync function because we don't
+				 * allow to drop the origin till the process owning the origin
+				 * is alive.
+				 *
+				 * There is a chance that the user is concurrently performing
+				 * refresh for the subscription where we remove the table
+				 * state and its origin and by this time the origin might be
+				 * already removed. So passing missing_ok = true.
+				 */
+				ReplicationOriginNameForTablesync(MyLogicalRepWorker->subid,
+												  rstate->relid,
+												  originname,
+												  sizeof(originname));
+				replorigin_drop_by_name(originname, true, false);
+
+				/*
+				 * Update the state to READY only after the origin cleanup.
+				 */
+				UpdateSubscriptionRelState(MyLogicalRepWorker->subid,
+										   rstate->relid, rstate->state,
+										   rstate->lsn);
+			}
+		}
+		else
+		{
+			LogicalRepWorker *syncworker;
+
+			/*
+			 * Look for a sync worker for this relation.
+			 */
+			LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
+			syncworker = logicalrep_worker_find(MyLogicalRepWorker->subid,
+												rstate->relid, false);
+
+			if (syncworker)
+			{
+				/* Found one, update our copy of its state */
+				SpinLockAcquire(&syncworker->relmutex);
+				rstate->state = syncworker->relstate;
+				rstate->lsn = syncworker->relstate_lsn;
+				if (rstate->state == SUBREL_STATE_SYNCWAIT)
+				{
+					/*
+					 * Sync worker is waiting for apply.  Tell sync worker it
+					 * can catchup now.
+					 */
+					syncworker->relstate = SUBREL_STATE_CATCHUP;
+					syncworker->relstate_lsn =
+						Max(syncworker->relstate_lsn, current_lsn);
+				}
+				SpinLockRelease(&syncworker->relmutex);
+
+				/* If we told worker to catch up, wait for it. */
+				if (rstate->state == SUBREL_STATE_SYNCWAIT)
+				{
+					/* Signal the sync worker, as it may be waiting for us. */
+					if (syncworker->proc)
+						logicalrep_worker_wakeup_ptr(syncworker);
+
+					/* Now safe to release the LWLock */
+					LWLockRelease(LogicalRepWorkerLock);
+
+					/*
+					 * Enter busy loop and wait for synchronization worker to
+					 * reach expected state (or die trying).
+					 */
+					if (!started_tx)
+					{
+						StartTransactionCommand();
+						started_tx = true;
+					}
+
+					wait_for_relation_state_change(rstate->relid,
+												   SUBREL_STATE_SYNCDONE);
+				}
+				else
+					LWLockRelease(LogicalRepWorkerLock);
+			}
+			else
+			{
+				/*
+				 * If there is no sync worker for this table yet, count
+				 * running sync workers for this subscription, while we have
+				 * the lock.
+				 */
+				int			nsyncworkers =
+				logicalrep_sync_worker_count(MyLogicalRepWorker->subid);
+
+				/* Now safe to release the LWLock */
+				LWLockRelease(LogicalRepWorkerLock);
+
+				/*
+				 * If there are free sync worker slot(s), start a new sync
+				 * worker for the table.
+				 */
+				if (nsyncworkers < max_sync_workers_per_subscription)
+				{
+					TimestampTz now = GetCurrentTimestamp();
+					struct tablesync_start_time_mapping *hentry;
+					bool		found;
+
+					hentry = hash_search(last_start_times, &rstate->relid,
+										 HASH_ENTER, &found);
+
+					if (!found ||
+						TimestampDifferenceExceeds(hentry->last_start_time, now,
+												   wal_retrieve_retry_interval))
+					{
+						logicalrep_worker_launch(MyLogicalRepWorker->dbid,
+												 MySubscription->oid,
+												 MySubscription->name,
+												 MyLogicalRepWorker->userid,
+												 rstate->relid);
+						hentry->last_start_time = now;
+					}
+				}
+			}
+		}
+	}
+
+	if (started_tx)
+	{
+		CommitTransactionCommand();
+		pgstat_report_stat(false);
+	}
+}
+
+/*
+ * Process possible state change(s) of tables that are being synchronized.
+ */
+void
+process_syncing_tables(XLogRecPtr current_lsn)
+{
+	if (am_tablesync_worker())
+		process_syncing_tables_for_sync(current_lsn);
+	else
+		process_syncing_tables_for_apply(current_lsn);
+}
+
+/*
+ * Create list of columns for COPY based on logical relation mapping.
+ */
+static List *
+make_copy_attnamelist(LogicalRepRelMapEntry *rel)
+{
+	List	   *attnamelist = NIL;
+	int			i;
+
+	for (i = 0; i < rel->remoterel.natts; i++)
+	{
+		attnamelist = lappend(attnamelist,
+							  makeString(rel->remoterel.attnames[i]));
+	}
+
+
+	return attnamelist;
+}
+
+/*
+ * Data source callback for the COPY FROM, which reads from the remote
+ * connection and passes the data back to our local COPY.
+ */
+static int
+copy_read_data(void *outbuf, int minread, int maxread)
+{
+	int			bytesread = 0;
+	int			avail;
+
+	/* If there are some leftover data from previous read, use it. */
+	avail = copybuf->len - copybuf->cursor;
+	if (avail)
+	{
+		if (avail > maxread)
+			avail = maxread;
+		memcpy(outbuf, &copybuf->data[copybuf->cursor], avail);
+		copybuf->cursor += avail;
+		maxread -= avail;
+		bytesread += avail;
+	}
+
+	while (maxread > 0 && bytesread < minread)
+	{
+		pgsocket	fd = PGINVALID_SOCKET;
+		int			len;
+		char	   *buf = NULL;
+
+		for (;;)
+		{
+			/* Try read the data. */
+			len = walrcv_receive(LogRepWorkerWalRcvConn, &buf, &fd);
+
+			CHECK_FOR_INTERRUPTS();
+
+			if (len == 0)
+				break;
+			else if (len < 0)
+				return bytesread;
+			else
+			{
+				/* Process the data */
+				copybuf->data = buf;
+				copybuf->len = len;
+				copybuf->cursor = 0;
+
+				avail = copybuf->len - copybuf->cursor;
+				if (avail > maxread)
+					avail = maxread;
+				memcpy(outbuf, &copybuf->data[copybuf->cursor], avail);
+				outbuf = (void *) ((char *) outbuf + avail);
+				copybuf->cursor += avail;
+				maxread -= avail;
+				bytesread += avail;
+			}
+
+			if (maxread <= 0 || bytesread >= minread)
+				return bytesread;
+		}
+
+		/*
+		 * Wait for more data or latch.
+		 */
+		(void) WaitLatchOrSocket(MyLatch,
+								 WL_SOCKET_READABLE | WL_LATCH_SET |
+								 WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+								 fd, 1000L, WAIT_EVENT_LOGICAL_SYNC_DATA);
+
+		ResetLatch(MyLatch);
+	}
+
+	return bytesread;
+}
+
+
+/*
+ * Get information about remote relation in similar fashion the RELATION
+ * message provides during replication.
+ */
+static void
+fetch_remote_table_info(char *nspname, char *relname,
+						LogicalRepRelation *lrel)
+{
+	WalRcvExecResult *res;
+	StringInfoData cmd;
+	TupleTableSlot *slot;
+	Oid			tableRow[] = {OIDOID, CHAROID, CHAROID};
+	Oid			attrRow[] = {TEXTOID, OIDOID, BOOLOID};
+	bool		isnull;
+	int			natt;
+
+	lrel->nspname = nspname;
+	lrel->relname = relname;
+
+	/* First fetch Oid and replica identity. */
+	initStringInfo(&cmd);
+	appendStringInfo(&cmd, "SELECT c.oid, c.relreplident, c.relkind"
+					 "  FROM pg_catalog.pg_class c"
+					 "  INNER JOIN pg_catalog.pg_namespace n"
+					 "        ON (c.relnamespace = n.oid)"
+					 " WHERE n.nspname = %s"
+					 "   AND c.relname = %s",
+					 quote_literal_cstr(nspname),
+					 quote_literal_cstr(relname));
+	res = walrcv_exec(LogRepWorkerWalRcvConn, cmd.data,
+					  lengthof(tableRow), tableRow);
+
+	if (res->status != WALRCV_OK_TUPLES)
+		ereport(ERROR,
+				(errcode(ERRCODE_CONNECTION_FAILURE),
+				 errmsg("could not fetch table info for table \"%s.%s\" from publisher: %s",
+						nspname, relname, res->err)));
+
+	slot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
+	if (!tuplestore_gettupleslot(res->tuplestore, true, false, slot))
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_OBJECT),
+				 errmsg("table \"%s.%s\" not found on publisher",
+						nspname, relname)));
+
+	lrel->remoteid = DatumGetObjectId(slot_getattr(slot, 1, &isnull));
+	Assert(!isnull);
+	lrel->replident = DatumGetChar(slot_getattr(slot, 2, &isnull));
+	Assert(!isnull);
+	lrel->relkind = DatumGetChar(slot_getattr(slot, 3, &isnull));
+	Assert(!isnull);
+
+	ExecDropSingleTupleTableSlot(slot);
+	walrcv_clear_result(res);
+
+	/* Now fetch columns. */
+	resetStringInfo(&cmd);
+	appendStringInfo(&cmd,
+					 "SELECT a.attname,"
+					 "       a.atttypid,"
+					 "       a.attnum = ANY(i.indkey)"
+					 "  FROM pg_catalog.pg_attribute a"
+					 "  LEFT JOIN pg_catalog.pg_index i"
+					 "       ON (i.indexrelid = pg_get_replica_identity_index(%u))"
+					 " WHERE a.attnum > 0::pg_catalog.int2"
+					 "   AND NOT a.attisdropped %s"
+					 "   AND a.attrelid = %u"
+					 " ORDER BY a.attnum",
+					 lrel->remoteid,
+					 (walrcv_server_version(LogRepWorkerWalRcvConn) >= 120000 ?
+					  "AND a.attgenerated = ''" : ""),
+					 lrel->remoteid);
+	res = walrcv_exec(LogRepWorkerWalRcvConn, cmd.data,
+					  lengthof(attrRow), attrRow);
+
+	if (res->status != WALRCV_OK_TUPLES)
+		ereport(ERROR,
+				(errcode(ERRCODE_CONNECTION_FAILURE),
+				 errmsg("could not fetch table info for table \"%s.%s\" from publisher: %s",
+						nspname, relname, res->err)));
+
+	/* We don't know the number of rows coming, so allocate enough space. */
+	lrel->attnames = palloc0(MaxTupleAttributeNumber * sizeof(char *));
+	lrel->atttyps = palloc0(MaxTupleAttributeNumber * sizeof(Oid));
+	lrel->attkeys = NULL;
+
+	natt = 0;
+	slot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
+	while (tuplestore_gettupleslot(res->tuplestore, true, false, slot))
+	{
+		lrel->attnames[natt] =
+			TextDatumGetCString(slot_getattr(slot, 1, &isnull));
+		Assert(!isnull);
+		lrel->atttyps[natt] = DatumGetObjectId(slot_getattr(slot, 2, &isnull));
+		Assert(!isnull);
+		if (DatumGetBool(slot_getattr(slot, 3, &isnull)))
+			lrel->attkeys = bms_add_member(lrel->attkeys, natt);
+
+		/* Should never happen. */
+		if (++natt >= MaxTupleAttributeNumber)
+			elog(ERROR, "too many columns in remote table \"%s.%s\"",
+				 nspname, relname);
+
+		ExecClearTuple(slot);
+	}
+	ExecDropSingleTupleTableSlot(slot);
+
+	lrel->natts = natt;
+
+	walrcv_clear_result(res);
+	pfree(cmd.data);
+}
+
+/*
+ * Copy existing data of a table from publisher.
+ *
+ * Caller is responsible for locking the local relation.
+ */
+static void
+copy_table(Relation rel)
+{
+	LogicalRepRelMapEntry *relmapentry;
+	LogicalRepRelation lrel;
+	WalRcvExecResult *res;
+	StringInfoData cmd;
+	CopyFromState cstate;
+	List	   *attnamelist;
+	ParseState *pstate;
+
+	/* Get the publisher relation info. */
+	fetch_remote_table_info(get_namespace_name(RelationGetNamespace(rel)),
+							RelationGetRelationName(rel), &lrel);
+
+	/* Put the relation into relmap. */
+	logicalrep_relmap_update(&lrel);
+
+	/* Map the publisher relation to local one. */
+	relmapentry = logicalrep_rel_open(lrel.remoteid, NoLock);
+	Assert(rel == relmapentry->localrel);
+
+	/* Start copy on the publisher. */
+	initStringInfo(&cmd);
+	if (lrel.relkind == RELKIND_RELATION)
+		appendStringInfo(&cmd, "COPY %s TO STDOUT",
+						 quote_qualified_identifier(lrel.nspname, lrel.relname));
+	else
+	{
+		/*
+		 * For non-tables, we need to do COPY (SELECT ...), but we can't just
+		 * do SELECT * because we need to not copy generated columns.
+		 */
+		appendStringInfoString(&cmd, "COPY (SELECT ");
+		for (int i = 0; i < lrel.natts; i++)
+		{
+			appendStringInfoString(&cmd, quote_identifier(lrel.attnames[i]));
+			if (i < lrel.natts - 1)
+				appendStringInfoString(&cmd, ", ");
+		}
+		appendStringInfo(&cmd, " FROM %s) TO STDOUT",
+						 quote_qualified_identifier(lrel.nspname, lrel.relname));
+	}
+	res = walrcv_exec(LogRepWorkerWalRcvConn, cmd.data, 0, NULL);
+	pfree(cmd.data);
+	if (res->status != WALRCV_OK_COPY_OUT)
+		ereport(ERROR,
+				(errcode(ERRCODE_CONNECTION_FAILURE),
+				 errmsg("could not start initial contents copy for table \"%s.%s\": %s",
+						lrel.nspname, lrel.relname, res->err)));
+	walrcv_clear_result(res);
+
+	copybuf = makeStringInfo();
+
+	pstate = make_parsestate(NULL);
+	(void) addRangeTableEntryForRelation(pstate, rel, AccessShareLock,
+										 NULL, false, false);
+
+	attnamelist = make_copy_attnamelist(relmapentry);
+	cstate = BeginCopyFrom(pstate, rel, NULL, NULL, false, copy_read_data, attnamelist, NIL);
+
+	/* Do the copy */
+	(void) CopyFrom(cstate);
+
+	logicalrep_rel_close(relmapentry, NoLock);
+}
+
+/*
+ * Determine the tablesync slot name.
+ *
+ * The name must not exceed NAMEDATALEN - 1 because of remote node constraints
+ * on slot name length. We append system_identifier to avoid slot_name
+ * collision with subscriptions in other clusters. With the current scheme
+ * pg_%u_sync_%u_UINT64_FORMAT (3 + 10 + 6 + 10 + 20 + '\0'), the maximum
+ * length of slot_name will be 50.
+ *
+ * The returned slot name is stored in the supplied buffer (syncslotname) with
+ * the given size.
+ *
+ * Note: We don't use the subscription slot name as part of tablesync slot name
+ * because we are responsible for cleaning up these slots and it could become
+ * impossible to recalculate what name to cleanup if the subscription slot name
+ * had changed.
+ */
+void
+ReplicationSlotNameForTablesync(Oid suboid, Oid relid,
+								char *syncslotname, int szslot)
+{
+	snprintf(syncslotname, szslot, "pg_%u_sync_%u_" UINT64_FORMAT, suboid,
+			 relid, GetSystemIdentifier());
+}
+
+/*
+ * Form the origin name for tablesync.
+ *
+ * Return the name in the supplied buffer.
+ */
+void
+ReplicationOriginNameForTablesync(Oid suboid, Oid relid,
+								  char *originname, int szorgname)
+{
+	snprintf(originname, szorgname, "pg_%u_%u", suboid, relid);
+}
+
+/*
+ * Start syncing the table in the sync worker.
+ *
+ * If nothing needs to be done to sync the table, we exit the worker without
+ * any further action.
+ *
+ * The returned slot name is palloc'ed in current memory context.
+ */
+char *
+LogicalRepSyncTableStart(XLogRecPtr *origin_startpos)
+{
+	char	   *slotname;
+	char	   *err;
+	char		relstate;
+	XLogRecPtr	relstate_lsn;
+	Relation	rel;
+	WalRcvExecResult *res;
+	char		originname[NAMEDATALEN];
+	RepOriginId originid;
+
+	/* Check the state of the table synchronization. */
+	StartTransactionCommand();
+	relstate = GetSubscriptionRelState(MyLogicalRepWorker->subid,
+									   MyLogicalRepWorker->relid,
+									   &relstate_lsn);
+	CommitTransactionCommand();
+
+	SpinLockAcquire(&MyLogicalRepWorker->relmutex);
+	MyLogicalRepWorker->relstate = relstate;
+	MyLogicalRepWorker->relstate_lsn = relstate_lsn;
+	SpinLockRelease(&MyLogicalRepWorker->relmutex);
+
+	/*
+	 * If synchronization is already done or no longer necessary, exit now
+	 * that we've updated shared memory state.
+	 */
+	switch (relstate)
+	{
+		case SUBREL_STATE_SYNCDONE:
+		case SUBREL_STATE_READY:
+		case SUBREL_STATE_UNKNOWN:
+			finish_sync_worker();	/* doesn't return */
+	}
+
+	/* Calculate the name of the tablesync slot. */
+	slotname = (char *) palloc(NAMEDATALEN);
+	ReplicationSlotNameForTablesync(MySubscription->oid,
+									MyLogicalRepWorker->relid,
+									slotname,
+									NAMEDATALEN);
+
+	/*
+	 * Here we use the slot name instead of the subscription name as the
+	 * application_name, so that it is different from the main apply worker,
+	 * so that synchronous replication can distinguish them.
+	 */
+	LogRepWorkerWalRcvConn =
+		walrcv_connect(MySubscription->conninfo, true, slotname, &err);
+	if (LogRepWorkerWalRcvConn == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_CONNECTION_FAILURE),
+				 errmsg("could not connect to the publisher: %s", err)));
+
+	Assert(MyLogicalRepWorker->relstate == SUBREL_STATE_INIT ||
+		   MyLogicalRepWorker->relstate == SUBREL_STATE_DATASYNC ||
+		   MyLogicalRepWorker->relstate == SUBREL_STATE_FINISHEDCOPY);
+
+	/* Assign the origin tracking record name. */
+	ReplicationOriginNameForTablesync(MySubscription->oid,
+									  MyLogicalRepWorker->relid,
+									  originname,
+									  sizeof(originname));
+
+	if (MyLogicalRepWorker->relstate == SUBREL_STATE_DATASYNC)
+	{
+		/*
+		 * We have previously errored out before finishing the copy so the
+		 * replication slot might exist. We want to remove the slot if it
+		 * already exists and proceed.
+		 *
+		 * XXX We could also instead try to drop the slot, last time we failed
+		 * but for that, we might need to clean up the copy state as it might
+		 * be in the middle of fetching the rows. Also, if there is a network
+		 * breakdown then it wouldn't have succeeded so trying it next time
+		 * seems like a better bet.
+		 */
+		ReplicationSlotDropAtPubNode(LogRepWorkerWalRcvConn, slotname, true);
+	}
+	else if (MyLogicalRepWorker->relstate == SUBREL_STATE_FINISHEDCOPY)
+	{
+		/*
+		 * The COPY phase was previously done, but tablesync then crashed
+		 * before it was able to finish normally.
+		 */
+		StartTransactionCommand();
+
+		/*
+		 * The origin tracking name must already exist. It was created first
+		 * time this tablesync was launched.
+		 */
+		originid = replorigin_by_name(originname, false);
+		replorigin_session_setup(originid);
+		replorigin_session_origin = originid;
+		*origin_startpos = replorigin_session_get_progress(false);
+
+		CommitTransactionCommand();
+
+		goto copy_table_done;
+	}
+
+	SpinLockAcquire(&MyLogicalRepWorker->relmutex);
+	MyLogicalRepWorker->relstate = SUBREL_STATE_DATASYNC;
+	MyLogicalRepWorker->relstate_lsn = InvalidXLogRecPtr;
+	SpinLockRelease(&MyLogicalRepWorker->relmutex);
+
+	/* Update the state and make it visible to others. */
+	StartTransactionCommand();
+	UpdateSubscriptionRelState(MyLogicalRepWorker->subid,
+							   MyLogicalRepWorker->relid,
+							   MyLogicalRepWorker->relstate,
+							   MyLogicalRepWorker->relstate_lsn);
+	CommitTransactionCommand();
+	pgstat_report_stat(false);
+
+	StartTransactionCommand();
+
+	/*
+	 * Use a standard write lock here. It might be better to disallow access
+	 * to the table while it's being synchronized. But we don't want to block
+	 * the main apply process from working and it has to open the relation in
+	 * RowExclusiveLock when remapping remote relation id to local one.
+	 */
+	rel = table_open(MyLogicalRepWorker->relid, RowExclusiveLock);
+
+	/*
+	 * Start a transaction in the remote node in REPEATABLE READ mode.  This
+	 * ensures that both the replication slot we create (see below) and the
+	 * COPY are consistent with each other.
+	 */
+	res = walrcv_exec(LogRepWorkerWalRcvConn,
+					  "BEGIN READ ONLY ISOLATION LEVEL REPEATABLE READ",
+					  0, NULL);
+	if (res->status != WALRCV_OK_COMMAND)
+		ereport(ERROR,
+				(errcode(ERRCODE_CONNECTION_FAILURE),
+				 errmsg("table copy could not start transaction on publisher: %s",
+						res->err)));
+	walrcv_clear_result(res);
+
+	/*
+	 * Create a new permanent logical decoding slot. This slot will be used
+	 * for the catchup phase after COPY is done, so tell it to use the
+	 * snapshot to make the final data consistent.
+	 *
+	 * Prevent cancel/die interrupts while creating slot here because it is
+	 * possible that before the server finishes this command, a concurrent
+	 * drop subscription happens which would complete without removing this
+	 * slot leading to a dangling slot on the server.
+	 */
+	HOLD_INTERRUPTS();
+	walrcv_create_slot(LogRepWorkerWalRcvConn, slotname, false /* permanent */ ,
+					   CRS_USE_SNAPSHOT, origin_startpos);
+	RESUME_INTERRUPTS();
+
+	/*
+	 * Setup replication origin tracking. The purpose of doing this before the
+	 * copy is to avoid doing the copy again due to any error in setting up
+	 * origin tracking.
+	 */
+	originid = replorigin_by_name(originname, true);
+	if (!OidIsValid(originid))
+	{
+		/*
+		 * Origin tracking does not exist, so create it now.
+		 *
+		 * Then advance to the LSN got from walrcv_create_slot. This is WAL
+		 * logged for the purpose of recovery. Locks are to prevent the
+		 * replication origin from vanishing while advancing.
+		 */
+		originid = replorigin_create(originname);
+
+		LockRelationOid(ReplicationOriginRelationId, RowExclusiveLock);
+		replorigin_advance(originid, *origin_startpos, InvalidXLogRecPtr,
+						   true /* go backward */ , true /* WAL log */ );
+		UnlockRelationOid(ReplicationOriginRelationId, RowExclusiveLock);
+
+		replorigin_session_setup(originid);
+		replorigin_session_origin = originid;
+	}
+	else
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_DUPLICATE_OBJECT),
+				 errmsg("replication origin \"%s\" already exists",
+						originname)));
+	}
+
+	/* Now do the initial data copy */
+	PushActiveSnapshot(GetTransactionSnapshot());
+	copy_table(rel);
+	PopActiveSnapshot();
+
+	res = walrcv_exec(LogRepWorkerWalRcvConn, "COMMIT", 0, NULL);
+	if (res->status != WALRCV_OK_COMMAND)
+		ereport(ERROR,
+				(errcode(ERRCODE_CONNECTION_FAILURE),
+				 errmsg("table copy could not finish transaction on publisher: %s",
+						res->err)));
+	walrcv_clear_result(res);
+
+	table_close(rel, NoLock);
+
+	/* Make the copy visible. */
+	CommandCounterIncrement();
+
+	/*
+	 * Update the persisted state to indicate the COPY phase is done; make it
+	 * visible to others.
+	 */
+	UpdateSubscriptionRelState(MyLogicalRepWorker->subid,
+							   MyLogicalRepWorker->relid,
+							   SUBREL_STATE_FINISHEDCOPY,
+							   MyLogicalRepWorker->relstate_lsn);
+
+	CommitTransactionCommand();
+
+copy_table_done:
+
+	elog(DEBUG1,
+		 "LogicalRepSyncTableStart: '%s' origin_startpos lsn %X/%X",
+		 originname, LSN_FORMAT_ARGS(*origin_startpos));
+
+	/*
+	 * We are done with the initial data synchronization, update the state.
+	 */
+	SpinLockAcquire(&MyLogicalRepWorker->relmutex);
+	MyLogicalRepWorker->relstate = SUBREL_STATE_SYNCWAIT;
+	MyLogicalRepWorker->relstate_lsn = *origin_startpos;
+	SpinLockRelease(&MyLogicalRepWorker->relmutex);
+
+	/*
+	 * Finally, wait until the main apply worker tells us to catch up and then
+	 * return to let LogicalRepApplyLoop do it.
+	 */
+	wait_for_worker_state_change(SUBREL_STATE_CATCHUP);
+	return slotname;
+}
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
new file mode 100644
index 0000000..8c9a4b5
--- /dev/null
+++ b/src/backend/replication/logical/worker.c
@@ -0,0 +1,3254 @@
+/*-------------------------------------------------------------------------
+ * worker.c
+ *	   PostgreSQL logical replication worker (apply)
+ *
+ * Copyright (c) 2016-2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/worker.c
+ *
+ * NOTES
+ *	  This file contains the worker which applies logical changes as they come
+ *	  from remote logical replication stream.
+ *
+ *	  The main worker (apply) is started by logical replication worker
+ *	  launcher for every enabled subscription in a database. It uses
+ *	  walsender protocol to communicate with publisher.
+ *
+ *	  This module includes server facing code and shares libpqwalreceiver
+ *	  module with walreceiver for providing the libpq specific functionality.
+ *
+ *
+ * STREAMED TRANSACTIONS
+ * ---------------------
+ * Streamed transactions (large transactions exceeding a memory limit on the
+ * upstream) are not applied immediately, but instead, the data is written
+ * to temporary files and then applied at once when the final commit arrives.
+ *
+ * Unlike the regular (non-streamed) case, handling streamed transactions has
+ * to handle aborts of both the toplevel transaction and subtransactions. This
+ * is achieved by tracking offsets for subtransactions, which is then used
+ * to truncate the file with serialized changes.
+ *
+ * The files are placed in tmp file directory by default, and the filenames
+ * include both the XID of the toplevel transaction and OID of the
+ * subscription. This is necessary so that different workers processing a
+ * remote transaction with the same XID doesn't interfere.
+ *
+ * We use BufFiles instead of using normal temporary files because (a) the
+ * BufFile infrastructure supports temporary files that exceed the OS file size
+ * limit, (b) provides a way for automatic clean up on the error and (c) provides
+ * a way to survive these files across local transactions and allow to open and
+ * close at stream start and close. We decided to use SharedFileSet
+ * infrastructure as without that it deletes the files on the closure of the
+ * file and if we decide to keep stream files open across the start/stop stream
+ * then it will consume a lot of memory (more than 8K for each BufFile and
+ * there could be multiple such BufFiles as the subscriber could receive
+ * multiple start/stop streams for different transactions before getting the
+ * commit). Moreover, if we don't use SharedFileSet then we also need to invent
+ * a new way to pass filenames to BufFile APIs so that we are allowed to open
+ * the file we desired across multiple stream-open calls for the same
+ * transaction.
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include "access/table.h"
+#include "access/tableam.h"
+#include "access/xact.h"
+#include "access/xlog_internal.h"
+#include "catalog/catalog.h"
+#include "catalog/namespace.h"
+#include "catalog/partition.h"
+#include "catalog/pg_inherits.h"
+#include "catalog/pg_subscription.h"
+#include "catalog/pg_subscription_rel.h"
+#include "catalog/pg_tablespace.h"
+#include "commands/tablecmds.h"
+#include "commands/tablespace.h"
+#include "commands/trigger.h"
+#include "executor/executor.h"
+#include "executor/execPartition.h"
+#include "executor/nodeModifyTable.h"
+#include "funcapi.h"
+#include "libpq/pqformat.h"
+#include "libpq/pqsignal.h"
+#include "mb/pg_wchar.h"
+#include "miscadmin.h"
+#include "nodes/makefuncs.h"
+#include "optimizer/optimizer.h"
+#include "pgstat.h"
+#include "postmaster/bgworker.h"
+#include "postmaster/interrupt.h"
+#include "postmaster/postmaster.h"
+#include "postmaster/walwriter.h"
+#include "replication/decode.h"
+#include "replication/logical.h"
+#include "replication/logicalproto.h"
+#include "replication/logicalrelation.h"
+#include "replication/logicalworker.h"
+#include "replication/origin.h"
+#include "replication/reorderbuffer.h"
+#include "replication/snapbuild.h"
+#include "replication/walreceiver.h"
+#include "replication/worker_internal.h"
+#include "rewrite/rewriteHandler.h"
+#include "storage/buffile.h"
+#include "storage/bufmgr.h"
+#include "storage/fd.h"
+#include "storage/ipc.h"
+#include "storage/lmgr.h"
+#include "storage/proc.h"
+#include "storage/procarray.h"
+#include "tcop/tcopprot.h"
+#include "utils/builtins.h"
+#include "utils/catcache.h"
+#include "utils/dynahash.h"
+#include "utils/datum.h"
+#include "utils/fmgroids.h"
+#include "utils/guc.h"
+#include "utils/inval.h"
+#include "utils/lsyscache.h"
+#include "utils/memutils.h"
+#include "utils/rel.h"
+#include "utils/syscache.h"
+#include "utils/timeout.h"
+
+#define NAPTIME_PER_CYCLE 1000	/* max sleep time between cycles (1s) */
+
+typedef struct FlushPosition
+{
+	dlist_node	node;
+	XLogRecPtr	local_end;
+	XLogRecPtr	remote_end;
+} FlushPosition;
+
+static dlist_head lsn_mapping = DLIST_STATIC_INIT(lsn_mapping);
+
+typedef struct SlotErrCallbackArg
+{
+	LogicalRepRelMapEntry *rel;
+	int			remote_attnum;
+} SlotErrCallbackArg;
+
+typedef struct ApplyExecutionData
+{
+	EState	   *estate;			/* executor state, used to track resources */
+
+	LogicalRepRelMapEntry *targetRel;	/* replication target rel */
+	ResultRelInfo *targetRelInfo;	/* ResultRelInfo for same */
+
+	/* These fields are used when the target relation is partitioned: */
+	ModifyTableState *mtstate;	/* dummy ModifyTable state */
+	PartitionTupleRouting *proute;	/* partition routing info */
+} ApplyExecutionData;
+
+/*
+ * Stream xid hash entry. Whenever we see a new xid we create this entry in the
+ * xidhash and along with it create the streaming file and store the fileset handle.
+ * The subxact file is created iff there is any subxact info under this xid. This
+ * entry is used on the subsequent streams for the xid to get the corresponding
+ * fileset handles, so storing them in hash makes the search faster.
+ */
+typedef struct StreamXidHash
+{
+	TransactionId xid;			/* xid is the hash key and must be first */
+	SharedFileSet *stream_fileset;	/* shared file set for stream data */
+	SharedFileSet *subxact_fileset; /* shared file set for subxact info */
+} StreamXidHash;
+
+static MemoryContext ApplyMessageContext = NULL;
+MemoryContext ApplyContext = NULL;
+
+/* per stream context for streaming transactions */
+static MemoryContext LogicalStreamingContext = NULL;
+
+WalReceiverConn *LogRepWorkerWalRcvConn = NULL;
+
+Subscription *MySubscription = NULL;
+bool		MySubscriptionValid = false;
+
+bool		in_remote_transaction = false;
+static XLogRecPtr remote_final_lsn = InvalidXLogRecPtr;
+
+/* fields valid only when processing streamed transaction */
+static bool in_streamed_transaction = false;
+
+static TransactionId stream_xid = InvalidTransactionId;
+
+/*
+ * Hash table for storing the streaming xid information along with shared file
+ * set for streaming and subxact files.
+ */
+static HTAB *xidhash = NULL;
+
+/* BufFile handle of the current streaming file */
+static BufFile *stream_fd = NULL;
+
+typedef struct SubXactInfo
+{
+	TransactionId xid;			/* XID of the subxact */
+	int			fileno;			/* file number in the buffile */
+	off_t		offset;			/* offset in the file */
+} SubXactInfo;
+
+/* Sub-transaction data for the current streaming transaction */
+typedef struct ApplySubXactData
+{
+	uint32		nsubxacts;		/* number of sub-transactions */
+	uint32		nsubxacts_max;	/* current capacity of subxacts */
+	TransactionId subxact_last; /* xid of the last sub-transaction */
+	SubXactInfo *subxacts;		/* sub-xact offset in changes file */
+} ApplySubXactData;
+
+static ApplySubXactData subxact_data = {0, 0, InvalidTransactionId, NULL};
+
+static inline void subxact_filename(char *path, Oid subid, TransactionId xid);
+static inline void changes_filename(char *path, Oid subid, TransactionId xid);
+
+/*
+ * Information about subtransactions of a given toplevel transaction.
+ */
+static void subxact_info_write(Oid subid, TransactionId xid);
+static void subxact_info_read(Oid subid, TransactionId xid);
+static void subxact_info_add(TransactionId xid);
+static inline void cleanup_subxact_info(void);
+
+/*
+ * Serialize and deserialize changes for a toplevel transaction.
+ */
+static void stream_cleanup_files(Oid subid, TransactionId xid);
+static void stream_open_file(Oid subid, TransactionId xid, bool first);
+static void stream_write_change(char action, StringInfo s);
+static void stream_close_file(void);
+
+static void send_feedback(XLogRecPtr recvpos, bool force, bool requestReply);
+
+static void store_flush_position(XLogRecPtr remote_lsn);
+
+static void maybe_reread_subscription(void);
+
+/* prototype needed because of stream_commit */
+static void apply_dispatch(StringInfo s);
+
+static void apply_handle_commit_internal(LogicalRepCommitData *commit_data);
+static void apply_handle_insert_internal(ApplyExecutionData *edata,
+										 ResultRelInfo *relinfo,
+										 TupleTableSlot *remoteslot);
+static void apply_handle_update_internal(ApplyExecutionData *edata,
+										 ResultRelInfo *relinfo,
+										 TupleTableSlot *remoteslot,
+										 LogicalRepTupleData *newtup);
+static void apply_handle_delete_internal(ApplyExecutionData *edata,
+										 ResultRelInfo *relinfo,
+										 TupleTableSlot *remoteslot);
+static bool FindReplTupleInLocalRel(EState *estate, Relation localrel,
+									LogicalRepRelation *remoterel,
+									TupleTableSlot *remoteslot,
+									TupleTableSlot **localslot);
+static void apply_handle_tuple_routing(ApplyExecutionData *edata,
+									   TupleTableSlot *remoteslot,
+									   LogicalRepTupleData *newtup,
+									   CmdType operation);
+
+/*
+ * Should this worker apply changes for given relation.
+ *
+ * This is mainly needed for initial relation data sync as that runs in
+ * separate worker process running in parallel and we need some way to skip
+ * changes coming to the main apply worker during the sync of a table.
+ *
+ * Note we need to do smaller or equals comparison for SYNCDONE state because
+ * it might hold position of end of initial slot consistent point WAL
+ * record + 1 (ie start of next record) and next record can be COMMIT of
+ * transaction we are now processing (which is what we set remote_final_lsn
+ * to in apply_handle_begin).
+ */
+static bool
+should_apply_changes_for_rel(LogicalRepRelMapEntry *rel)
+{
+	if (am_tablesync_worker())
+		return MyLogicalRepWorker->relid == rel->localreloid;
+	else
+		return (rel->state == SUBREL_STATE_READY ||
+				(rel->state == SUBREL_STATE_SYNCDONE &&
+				 rel->statelsn <= remote_final_lsn));
+}
+
+/*
+ * Begin one step (one INSERT, UPDATE, etc) of a replication transaction.
+ *
+ * Start a transaction, if this is the first step (else we keep using the
+ * existing transaction).
+ * Also provide a global snapshot and ensure we run in ApplyMessageContext.
+ */
+static void
+begin_replication_step(void)
+{
+	SetCurrentStatementStartTimestamp();
+
+	if (!IsTransactionState())
+	{
+		StartTransactionCommand();
+		maybe_reread_subscription();
+	}
+
+	PushActiveSnapshot(GetTransactionSnapshot());
+
+	MemoryContextSwitchTo(ApplyMessageContext);
+}
+
+/*
+ * Finish up one step of a replication transaction.
+ * Callers of begin_replication_step() must also call this.
+ *
+ * We don't close out the transaction here, but we should increment
+ * the command counter to make the effects of this step visible.
+ */
+static void
+end_replication_step(void)
+{
+	PopActiveSnapshot();
+
+	CommandCounterIncrement();
+}
+
+/*
+ * Handle streamed transactions.
+ *
+ * If in streaming mode (receiving a block of streamed transaction), we
+ * simply redirect it to a file for the proper toplevel transaction.
+ *
+ * Returns true for streamed transactions, false otherwise (regular mode).
+ */
+static bool
+handle_streamed_transaction(LogicalRepMsgType action, StringInfo s)
+{
+	TransactionId xid;
+
+	/* not in streaming mode */
+	if (!in_streamed_transaction)
+		return false;
+
+	Assert(stream_fd != NULL);
+	Assert(TransactionIdIsValid(stream_xid));
+
+	/*
+	 * We should have received XID of the subxact as the first part of the
+	 * message, so extract it.
+	 */
+	xid = pq_getmsgint(s, 4);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid transaction ID in streamed replication transaction")));
+
+	/* Add the new subxact to the array (unless already there). */
+	subxact_info_add(xid);
+
+	/* write the change to the current file */
+	stream_write_change(action, s);
+
+	return true;
+}
+
+/*
+ * Executor state preparation for evaluation of constraint expressions,
+ * indexes and triggers for the specified relation.
+ *
+ * Note that the caller must open and close any indexes to be updated.
+ */
+static ApplyExecutionData *
+create_edata_for_relation(LogicalRepRelMapEntry *rel)
+{
+	ApplyExecutionData *edata;
+	EState	   *estate;
+	RangeTblEntry *rte;
+	ResultRelInfo *resultRelInfo;
+
+	edata = (ApplyExecutionData *) palloc0(sizeof(ApplyExecutionData));
+	edata->targetRel = rel;
+
+	edata->estate = estate = CreateExecutorState();
+
+	rte = makeNode(RangeTblEntry);
+	rte->rtekind = RTE_RELATION;
+	rte->relid = RelationGetRelid(rel->localrel);
+	rte->relkind = rel->localrel->rd_rel->relkind;
+	rte->rellockmode = AccessShareLock;
+	ExecInitRangeTable(estate, list_make1(rte));
+
+	edata->targetRelInfo = resultRelInfo = makeNode(ResultRelInfo);
+
+	/*
+	 * Use Relation opened by logicalrep_rel_open() instead of opening it
+	 * again.
+	 */
+	InitResultRelInfo(resultRelInfo, rel->localrel, 1, NULL, 0);
+
+	/*
+	 * We put the ResultRelInfo in the es_opened_result_relations list, even
+	 * though we don't populate the es_result_relations array.  That's a bit
+	 * bogus, but it's enough to make ExecGetTriggerResultRel() find them.
+	 *
+	 * ExecOpenIndices() is not called here either, each execution path doing
+	 * an apply operation being responsible for that.
+	 */
+	estate->es_opened_result_relations =
+		lappend(estate->es_opened_result_relations, resultRelInfo);
+
+	estate->es_output_cid = GetCurrentCommandId(true);
+
+	/* Prepare to catch AFTER triggers. */
+	AfterTriggerBeginQuery();
+
+	/* other fields of edata remain NULL for now */
+
+	return edata;
+}
+
+/*
+ * Finish any operations related to the executor state created by
+ * create_edata_for_relation().
+ */
+static void
+finish_edata(ApplyExecutionData *edata)
+{
+	EState	   *estate = edata->estate;
+
+	/* Handle any queued AFTER triggers. */
+	AfterTriggerEndQuery(estate);
+
+	/* Shut down tuple routing, if any was done. */
+	if (edata->proute)
+		ExecCleanupTupleRouting(edata->mtstate, edata->proute);
+
+	/*
+	 * Cleanup.  It might seem that we should call ExecCloseResultRelations()
+	 * here, but we intentionally don't.  It would close the rel we added to
+	 * es_opened_result_relations above, which is wrong because we took no
+	 * corresponding refcount.  We rely on ExecCleanupTupleRouting() to close
+	 * any other relations opened during execution.
+	 */
+	ExecResetTupleTable(estate->es_tupleTable, false);
+	FreeExecutorState(estate);
+	pfree(edata);
+}
+
+/*
+ * Executes default values for columns for which we can't map to remote
+ * relation columns.
+ *
+ * This allows us to support tables which have more columns on the downstream
+ * than on the upstream.
+ */
+static void
+slot_fill_defaults(LogicalRepRelMapEntry *rel, EState *estate,
+				   TupleTableSlot *slot)
+{
+	TupleDesc	desc = RelationGetDescr(rel->localrel);
+	int			num_phys_attrs = desc->natts;
+	int			i;
+	int			attnum,
+				num_defaults = 0;
+	int		   *defmap;
+	ExprState **defexprs;
+	ExprContext *econtext;
+
+	econtext = GetPerTupleExprContext(estate);
+
+	/* We got all the data via replication, no need to evaluate anything. */
+	if (num_phys_attrs == rel->remoterel.natts)
+		return;
+
+	defmap = (int *) palloc(num_phys_attrs * sizeof(int));
+	defexprs = (ExprState **) palloc(num_phys_attrs * sizeof(ExprState *));
+
+	Assert(rel->attrmap->maplen == num_phys_attrs);
+	for (attnum = 0; attnum < num_phys_attrs; attnum++)
+	{
+		Expr	   *defexpr;
+
+		if (TupleDescAttr(desc, attnum)->attisdropped || TupleDescAttr(desc, attnum)->attgenerated)
+			continue;
+
+		if (rel->attrmap->attnums[attnum] >= 0)
+			continue;
+
+		defexpr = (Expr *) build_column_default(rel->localrel, attnum + 1);
+
+		if (defexpr != NULL)
+		{
+			/* Run the expression through planner */
+			defexpr = expression_planner(defexpr);
+
+			/* Initialize executable expression in copycontext */
+			defexprs[num_defaults] = ExecInitExpr(defexpr, NULL);
+			defmap[num_defaults] = attnum;
+			num_defaults++;
+		}
+
+	}
+
+	for (i = 0; i < num_defaults; i++)
+		slot->tts_values[defmap[i]] =
+			ExecEvalExpr(defexprs[i], econtext, &slot->tts_isnull[defmap[i]]);
+}
+
+/*
+ * Error callback to give more context info about data conversion failures
+ * while reading data from the remote server.
+ */
+static void
+slot_store_error_callback(void *arg)
+{
+	SlotErrCallbackArg *errarg = (SlotErrCallbackArg *) arg;
+	LogicalRepRelMapEntry *rel;
+
+	/* Nothing to do if remote attribute number is not set */
+	if (errarg->remote_attnum < 0)
+		return;
+
+	rel = errarg->rel;
+	errcontext("processing remote data for replication target relation \"%s.%s\" column \"%s\"",
+			   rel->remoterel.nspname, rel->remoterel.relname,
+			   rel->remoterel.attnames[errarg->remote_attnum]);
+}
+
+/*
+ * Store tuple data into slot.
+ *
+ * Incoming data can be either text or binary format.
+ */
+static void
+slot_store_data(TupleTableSlot *slot, LogicalRepRelMapEntry *rel,
+				LogicalRepTupleData *tupleData)
+{
+	int			natts = slot->tts_tupleDescriptor->natts;
+	int			i;
+	SlotErrCallbackArg errarg;
+	ErrorContextCallback errcallback;
+
+	ExecClearTuple(slot);
+
+	/* Push callback + info on the error context stack */
+	errarg.rel = rel;
+	errarg.remote_attnum = -1;
+	errcallback.callback = slot_store_error_callback;
+	errcallback.arg = (void *) &errarg;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* Call the "in" function for each non-dropped, non-null attribute */
+	Assert(natts == rel->attrmap->maplen);
+	for (i = 0; i < natts; i++)
+	{
+		Form_pg_attribute att = TupleDescAttr(slot->tts_tupleDescriptor, i);
+		int			remoteattnum = rel->attrmap->attnums[i];
+
+		if (!att->attisdropped && remoteattnum >= 0)
+		{
+			StringInfo	colvalue = &tupleData->colvalues[remoteattnum];
+
+			Assert(remoteattnum < tupleData->ncols);
+
+			errarg.remote_attnum = remoteattnum;
+
+			if (tupleData->colstatus[remoteattnum] == LOGICALREP_COLUMN_TEXT)
+			{
+				Oid			typinput;
+				Oid			typioparam;
+
+				getTypeInputInfo(att->atttypid, &typinput, &typioparam);
+				slot->tts_values[i] =
+					OidInputFunctionCall(typinput, colvalue->data,
+										 typioparam, att->atttypmod);
+				slot->tts_isnull[i] = false;
+			}
+			else if (tupleData->colstatus[remoteattnum] == LOGICALREP_COLUMN_BINARY)
+			{
+				Oid			typreceive;
+				Oid			typioparam;
+
+				/*
+				 * In some code paths we may be asked to re-parse the same
+				 * tuple data.  Reset the StringInfo's cursor so that works.
+				 */
+				colvalue->cursor = 0;
+
+				getTypeBinaryInputInfo(att->atttypid, &typreceive, &typioparam);
+				slot->tts_values[i] =
+					OidReceiveFunctionCall(typreceive, colvalue,
+										   typioparam, att->atttypmod);
+
+				/* Trouble if it didn't eat the whole buffer */
+				if (colvalue->cursor != colvalue->len)
+					ereport(ERROR,
+							(errcode(ERRCODE_INVALID_BINARY_REPRESENTATION),
+							 errmsg("incorrect binary data format in logical replication column %d",
+									remoteattnum + 1)));
+				slot->tts_isnull[i] = false;
+			}
+			else
+			{
+				/*
+				 * NULL value from remote.  (We don't expect to see
+				 * LOGICALREP_COLUMN_UNCHANGED here, but if we do, treat it as
+				 * NULL.)
+				 */
+				slot->tts_values[i] = (Datum) 0;
+				slot->tts_isnull[i] = true;
+			}
+
+			errarg.remote_attnum = -1;
+		}
+		else
+		{
+			/*
+			 * We assign NULL to dropped attributes and missing values
+			 * (missing values should be later filled using
+			 * slot_fill_defaults).
+			 */
+			slot->tts_values[i] = (Datum) 0;
+			slot->tts_isnull[i] = true;
+		}
+	}
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+
+	ExecStoreVirtualTuple(slot);
+}
+
+/*
+ * Replace updated columns with data from the LogicalRepTupleData struct.
+ * This is somewhat similar to heap_modify_tuple but also calls the type
+ * input functions on the user data.
+ *
+ * "slot" is filled with a copy of the tuple in "srcslot", replacing
+ * columns provided in "tupleData" and leaving others as-is.
+ *
+ * Caution: unreplaced pass-by-ref columns in "slot" will point into the
+ * storage for "srcslot".  This is OK for current usage, but someday we may
+ * need to materialize "slot" at the end to make it independent of "srcslot".
+ */
+static void
+slot_modify_data(TupleTableSlot *slot, TupleTableSlot *srcslot,
+				 LogicalRepRelMapEntry *rel,
+				 LogicalRepTupleData *tupleData)
+{
+	int			natts = slot->tts_tupleDescriptor->natts;
+	int			i;
+	SlotErrCallbackArg errarg;
+	ErrorContextCallback errcallback;
+
+	/* We'll fill "slot" with a virtual tuple, so we must start with ... */
+	ExecClearTuple(slot);
+
+	/*
+	 * Copy all the column data from srcslot, so that we'll have valid values
+	 * for unreplaced columns.
+	 */
+	Assert(natts == srcslot->tts_tupleDescriptor->natts);
+	slot_getallattrs(srcslot);
+	memcpy(slot->tts_values, srcslot->tts_values, natts * sizeof(Datum));
+	memcpy(slot->tts_isnull, srcslot->tts_isnull, natts * sizeof(bool));
+
+	/* For error reporting, push callback + info on the error context stack */
+	errarg.rel = rel;
+	errarg.remote_attnum = -1;
+	errcallback.callback = slot_store_error_callback;
+	errcallback.arg = (void *) &errarg;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* Call the "in" function for each replaced attribute */
+	Assert(natts == rel->attrmap->maplen);
+	for (i = 0; i < natts; i++)
+	{
+		Form_pg_attribute att = TupleDescAttr(slot->tts_tupleDescriptor, i);
+		int			remoteattnum = rel->attrmap->attnums[i];
+
+		if (remoteattnum < 0)
+			continue;
+
+		Assert(remoteattnum < tupleData->ncols);
+
+		if (tupleData->colstatus[remoteattnum] != LOGICALREP_COLUMN_UNCHANGED)
+		{
+			StringInfo	colvalue = &tupleData->colvalues[remoteattnum];
+
+			errarg.remote_attnum = remoteattnum;
+
+			if (tupleData->colstatus[remoteattnum] == LOGICALREP_COLUMN_TEXT)
+			{
+				Oid			typinput;
+				Oid			typioparam;
+
+				getTypeInputInfo(att->atttypid, &typinput, &typioparam);
+				slot->tts_values[i] =
+					OidInputFunctionCall(typinput, colvalue->data,
+										 typioparam, att->atttypmod);
+				slot->tts_isnull[i] = false;
+			}
+			else if (tupleData->colstatus[remoteattnum] == LOGICALREP_COLUMN_BINARY)
+			{
+				Oid			typreceive;
+				Oid			typioparam;
+
+				/*
+				 * In some code paths we may be asked to re-parse the same
+				 * tuple data.  Reset the StringInfo's cursor so that works.
+				 */
+				colvalue->cursor = 0;
+
+				getTypeBinaryInputInfo(att->atttypid, &typreceive, &typioparam);
+				slot->tts_values[i] =
+					OidReceiveFunctionCall(typreceive, colvalue,
+										   typioparam, att->atttypmod);
+
+				/* Trouble if it didn't eat the whole buffer */
+				if (colvalue->cursor != colvalue->len)
+					ereport(ERROR,
+							(errcode(ERRCODE_INVALID_BINARY_REPRESENTATION),
+							 errmsg("incorrect binary data format in logical replication column %d",
+									remoteattnum + 1)));
+				slot->tts_isnull[i] = false;
+			}
+			else
+			{
+				/* must be LOGICALREP_COLUMN_NULL */
+				slot->tts_values[i] = (Datum) 0;
+				slot->tts_isnull[i] = true;
+			}
+
+			errarg.remote_attnum = -1;
+		}
+	}
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+
+	/* And finally, declare that "slot" contains a valid virtual tuple */
+	ExecStoreVirtualTuple(slot);
+}
+
+/*
+ * Handle BEGIN message.
+ */
+static void
+apply_handle_begin(StringInfo s)
+{
+	LogicalRepBeginData begin_data;
+
+	logicalrep_read_begin(s, &begin_data);
+
+	remote_final_lsn = begin_data.final_lsn;
+
+	in_remote_transaction = true;
+
+	pgstat_report_activity(STATE_RUNNING, NULL);
+}
+
+/*
+ * Handle COMMIT message.
+ *
+ * TODO, support tracking of multiple origins
+ */
+static void
+apply_handle_commit(StringInfo s)
+{
+	LogicalRepCommitData commit_data;
+
+	logicalrep_read_commit(s, &commit_data);
+
+	if (commit_data.commit_lsn != remote_final_lsn)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("incorrect commit LSN %X/%X in commit message (expected %X/%X)",
+								 LSN_FORMAT_ARGS(commit_data.commit_lsn),
+								 LSN_FORMAT_ARGS(remote_final_lsn))));
+
+	apply_handle_commit_internal(&commit_data);
+
+	/* Process any tables that are being synchronized in parallel. */
+	process_syncing_tables(commit_data.end_lsn);
+
+	pgstat_report_activity(STATE_IDLE, NULL);
+}
+
+/*
+ * Handle ORIGIN message.
+ *
+ * TODO, support tracking of multiple origins
+ */
+static void
+apply_handle_origin(StringInfo s)
+{
+	/*
+	 * ORIGIN message can only come inside streaming transaction or inside
+	 * remote transaction and before any actual writes.
+	 */
+	if (!in_streamed_transaction &&
+		(!in_remote_transaction ||
+		 (IsTransactionState() && !am_tablesync_worker())))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("ORIGIN message sent out of order")));
+}
+
+/*
+ * Handle STREAM START message.
+ */
+static void
+apply_handle_stream_start(StringInfo s)
+{
+	bool		first_segment;
+	HASHCTL		hash_ctl;
+
+	if (in_streamed_transaction)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("duplicate STREAM START message")));
+
+	/*
+	 * Start a transaction on stream start, this transaction will be committed
+	 * on the stream stop unless it is a tablesync worker in which case it
+	 * will be committed after processing all the messages. We need the
+	 * transaction for handling the buffile, used for serializing the
+	 * streaming data and subxact info.
+	 */
+	begin_replication_step();
+
+	/* notify handle methods we're processing a remote transaction */
+	in_streamed_transaction = true;
+
+	/* extract XID of the top-level transaction */
+	stream_xid = logicalrep_read_stream_start(s, &first_segment);
+
+	if (!TransactionIdIsValid(stream_xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid transaction ID in streamed replication transaction")));
+
+	/*
+	 * Initialize the xidhash table if we haven't yet. This will be used for
+	 * the entire duration of the apply worker so create it in permanent
+	 * context.
+	 */
+	if (xidhash == NULL)
+	{
+		hash_ctl.keysize = sizeof(TransactionId);
+		hash_ctl.entrysize = sizeof(StreamXidHash);
+		hash_ctl.hcxt = ApplyContext;
+		xidhash = hash_create("StreamXidHash", 1024, &hash_ctl,
+							  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+	}
+
+	/* open the spool file for this transaction */
+	stream_open_file(MyLogicalRepWorker->subid, stream_xid, first_segment);
+
+	/* if this is not the first segment, open existing subxact file */
+	if (!first_segment)
+		subxact_info_read(MyLogicalRepWorker->subid, stream_xid);
+
+	pgstat_report_activity(STATE_RUNNING, NULL);
+
+	end_replication_step();
+}
+
+/*
+ * Handle STREAM STOP message.
+ */
+static void
+apply_handle_stream_stop(StringInfo s)
+{
+	if (!in_streamed_transaction)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("STREAM STOP message without STREAM START")));
+
+	/*
+	 * Close the file with serialized changes, and serialize information about
+	 * subxacts for the toplevel transaction.
+	 */
+	subxact_info_write(MyLogicalRepWorker->subid, stream_xid);
+	stream_close_file();
+
+	/* We must be in a valid transaction state */
+	Assert(IsTransactionState());
+
+	/* Commit the per-stream transaction */
+	CommitTransactionCommand();
+
+	in_streamed_transaction = false;
+
+	/* Reset per-stream context */
+	MemoryContextReset(LogicalStreamingContext);
+
+	pgstat_report_activity(STATE_IDLE, NULL);
+}
+
+/*
+ * Handle STREAM abort message.
+ */
+static void
+apply_handle_stream_abort(StringInfo s)
+{
+	TransactionId xid;
+	TransactionId subxid;
+
+	if (in_streamed_transaction)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("STREAM ABORT message without STREAM STOP")));
+
+	logicalrep_read_stream_abort(s, &xid, &subxid);
+
+	/*
+	 * If the two XIDs are the same, it's in fact abort of toplevel xact, so
+	 * just delete the files with serialized info.
+	 */
+	if (xid == subxid)
+		stream_cleanup_files(MyLogicalRepWorker->subid, xid);
+	else
+	{
+		/*
+		 * OK, so it's a subxact. We need to read the subxact file for the
+		 * toplevel transaction, determine the offset tracked for the subxact,
+		 * and truncate the file with changes. We also remove the subxacts
+		 * with higher offsets (or rather higher XIDs).
+		 *
+		 * We intentionally scan the array from the tail, because we're likely
+		 * aborting a change for the most recent subtransactions.
+		 *
+		 * We can't use the binary search here as subxact XIDs won't
+		 * necessarily arrive in sorted order, consider the case where we have
+		 * released the savepoint for multiple subtransactions and then
+		 * performed rollback to savepoint for one of the earlier
+		 * sub-transaction.
+		 */
+		int64		i;
+		int64		subidx;
+		BufFile    *fd;
+		bool		found = false;
+		char		path[MAXPGPATH];
+		StreamXidHash *ent;
+
+		subidx = -1;
+		begin_replication_step();
+		subxact_info_read(MyLogicalRepWorker->subid, xid);
+
+		for (i = subxact_data.nsubxacts; i > 0; i--)
+		{
+			if (subxact_data.subxacts[i - 1].xid == subxid)
+			{
+				subidx = (i - 1);
+				found = true;
+				break;
+			}
+		}
+
+		/*
+		 * If it's an empty sub-transaction then we will not find the subxid
+		 * here so just cleanup the subxact info and return.
+		 */
+		if (!found)
+		{
+			/* Cleanup the subxact info */
+			cleanup_subxact_info();
+			end_replication_step();
+			CommitTransactionCommand();
+			return;
+		}
+
+		ent = (StreamXidHash *) hash_search(xidhash,
+											(void *) &xid,
+											HASH_FIND,
+											NULL);
+		if (!ent)
+			ereport(ERROR,
+					(errcode(ERRCODE_PROTOCOL_VIOLATION),
+					 errmsg_internal("transaction %u not found in stream XID hash table",
+									 xid)));
+
+		/* open the changes file */
+		changes_filename(path, MyLogicalRepWorker->subid, xid);
+		fd = BufFileOpenShared(ent->stream_fileset, path, O_RDWR);
+
+		/* OK, truncate the file at the right offset */
+		BufFileTruncateShared(fd, subxact_data.subxacts[subidx].fileno,
+							  subxact_data.subxacts[subidx].offset);
+		BufFileClose(fd);
+
+		/* discard the subxacts added later */
+		subxact_data.nsubxacts = subidx;
+
+		/* write the updated subxact list */
+		subxact_info_write(MyLogicalRepWorker->subid, xid);
+
+		end_replication_step();
+		CommitTransactionCommand();
+	}
+}
+
+/*
+ * Handle STREAM COMMIT message.
+ */
+static void
+apply_handle_stream_commit(StringInfo s)
+{
+	TransactionId xid;
+	StringInfoData s2;
+	int			nchanges;
+	char		path[MAXPGPATH];
+	char	   *buffer = NULL;
+	LogicalRepCommitData commit_data;
+	StreamXidHash *ent;
+	MemoryContext oldcxt;
+	BufFile    *fd;
+
+	if (in_streamed_transaction)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("STREAM COMMIT message without STREAM STOP")));
+
+	xid = logicalrep_read_stream_commit(s, &commit_data);
+
+	elog(DEBUG1, "received commit for streamed transaction %u", xid);
+
+	/* Make sure we have an open transaction */
+	begin_replication_step();
+
+	/*
+	 * Allocate file handle and memory required to process all the messages in
+	 * TopTransactionContext to avoid them getting reset after each message is
+	 * processed.
+	 */
+	oldcxt = MemoryContextSwitchTo(TopTransactionContext);
+
+	/* open the spool file for the committed transaction */
+	changes_filename(path, MyLogicalRepWorker->subid, xid);
+	elog(DEBUG1, "replaying changes from file \"%s\"", path);
+
+	ent = (StreamXidHash *) hash_search(xidhash,
+										(void *) &xid,
+										HASH_FIND,
+										NULL);
+	if (!ent)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("transaction %u not found in stream XID hash table",
+								 xid)));
+
+	fd = BufFileOpenShared(ent->stream_fileset, path, O_RDONLY);
+
+	buffer = palloc(BLCKSZ);
+	initStringInfo(&s2);
+
+	MemoryContextSwitchTo(oldcxt);
+
+	remote_final_lsn = commit_data.commit_lsn;
+
+	/*
+	 * Make sure the handle apply_dispatch methods are aware we're in a remote
+	 * transaction.
+	 */
+	in_remote_transaction = true;
+	pgstat_report_activity(STATE_RUNNING, NULL);
+
+	end_replication_step();
+
+	/*
+	 * Read the entries one by one and pass them through the same logic as in
+	 * apply_dispatch.
+	 */
+	nchanges = 0;
+	while (true)
+	{
+		int			nbytes;
+		int			len;
+
+		CHECK_FOR_INTERRUPTS();
+
+		/* read length of the on-disk record */
+		nbytes = BufFileRead(fd, &len, sizeof(len));
+
+		/* have we reached end of the file? */
+		if (nbytes == 0)
+			break;
+
+		/* do we have a correct length? */
+		if (nbytes != sizeof(len))
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read from streaming transaction's changes file \"%s\": %m",
+							path)));
+
+		if (len <= 0)
+			elog(ERROR, "incorrect length %d in streaming transaction's changes file \"%s\"",
+				 len, path);
+
+		/* make sure we have sufficiently large buffer */
+		buffer = repalloc(buffer, len);
+
+		/* and finally read the data into the buffer */
+		if (BufFileRead(fd, buffer, len) != len)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read from streaming transaction's changes file \"%s\": %m",
+							path)));
+
+		/* copy the buffer to the stringinfo and call apply_dispatch */
+		resetStringInfo(&s2);
+		appendBinaryStringInfo(&s2, buffer, len);
+
+		/* Ensure we are reading the data into our memory context. */
+		oldcxt = MemoryContextSwitchTo(ApplyMessageContext);
+
+		apply_dispatch(&s2);
+
+		MemoryContextReset(ApplyMessageContext);
+
+		MemoryContextSwitchTo(oldcxt);
+
+		nchanges++;
+
+		if (nchanges % 1000 == 0)
+			elog(DEBUG1, "replayed %d changes from file \"%s\"",
+				 nchanges, path);
+	}
+
+	BufFileClose(fd);
+
+	pfree(buffer);
+	pfree(s2.data);
+
+	elog(DEBUG1, "replayed %d (all) changes from file \"%s\"",
+		 nchanges, path);
+
+	apply_handle_commit_internal(&commit_data);
+
+	/* unlink the files with serialized changes and subxact info */
+	stream_cleanup_files(MyLogicalRepWorker->subid, xid);
+
+	/* Process any tables that are being synchronized in parallel. */
+	process_syncing_tables(commit_data.end_lsn);
+
+	pgstat_report_activity(STATE_IDLE, NULL);
+}
+
+/*
+ * Helper function for apply_handle_commit and apply_handle_stream_commit.
+ */
+static void
+apply_handle_commit_internal(LogicalRepCommitData *commit_data)
+{
+	if (IsTransactionState())
+	{
+		/*
+		 * Update origin state so we can restart streaming from correct
+		 * position in case of crash.
+		 */
+		replorigin_session_origin_lsn = commit_data->end_lsn;
+		replorigin_session_origin_timestamp = commit_data->committime;
+
+		CommitTransactionCommand();
+		pgstat_report_stat(false);
+
+		store_flush_position(commit_data->end_lsn);
+	}
+	else
+	{
+		/* Process any invalidation messages that might have accumulated. */
+		AcceptInvalidationMessages();
+		maybe_reread_subscription();
+	}
+
+	in_remote_transaction = false;
+}
+
+/*
+ * Handle RELATION message.
+ *
+ * Note we don't do validation against local schema here. The validation
+ * against local schema is postponed until first change for given relation
+ * comes as we only care about it when applying changes for it anyway and we
+ * do less locking this way.
+ */
+static void
+apply_handle_relation(StringInfo s)
+{
+	LogicalRepRelation *rel;
+
+	if (handle_streamed_transaction(LOGICAL_REP_MSG_RELATION, s))
+		return;
+
+	rel = logicalrep_read_rel(s);
+	logicalrep_relmap_update(rel);
+
+	/* Also reset all entries in the partition map that refer to remoterel. */
+	logicalrep_partmap_reset_relmap(rel);
+}
+
+/*
+ * Handle TYPE message.
+ *
+ * This implementation pays no attention to TYPE messages; we expect the user
+ * to have set things up so that the incoming data is acceptable to the input
+ * functions for the locally subscribed tables.  Hence, we just read and
+ * discard the message.
+ */
+static void
+apply_handle_type(StringInfo s)
+{
+	LogicalRepTyp typ;
+
+	if (handle_streamed_transaction(LOGICAL_REP_MSG_TYPE, s))
+		return;
+
+	logicalrep_read_typ(s, &typ);
+}
+
+/*
+ * Get replica identity index or if it is not defined a primary key.
+ *
+ * If neither is defined, returns InvalidOid
+ */
+static Oid
+GetRelationIdentityOrPK(Relation rel)
+{
+	Oid			idxoid;
+
+	idxoid = RelationGetReplicaIndex(rel);
+
+	if (!OidIsValid(idxoid))
+		idxoid = RelationGetPrimaryKeyIndex(rel);
+
+	return idxoid;
+}
+
+/*
+ * Handle INSERT message.
+ */
+
+static void
+apply_handle_insert(StringInfo s)
+{
+	LogicalRepRelMapEntry *rel;
+	LogicalRepTupleData newtup;
+	LogicalRepRelId relid;
+	ApplyExecutionData *edata;
+	EState	   *estate;
+	TupleTableSlot *remoteslot;
+	MemoryContext oldctx;
+
+	if (handle_streamed_transaction(LOGICAL_REP_MSG_INSERT, s))
+		return;
+
+	begin_replication_step();
+
+	relid = logicalrep_read_insert(s, &newtup);
+	rel = logicalrep_rel_open(relid, RowExclusiveLock);
+	if (!should_apply_changes_for_rel(rel))
+	{
+		/*
+		 * The relation can't become interesting in the middle of the
+		 * transaction so it's safe to unlock it.
+		 */
+		logicalrep_rel_close(rel, RowExclusiveLock);
+		end_replication_step();
+		return;
+	}
+
+	/* Initialize the executor state. */
+	edata = create_edata_for_relation(rel);
+	estate = edata->estate;
+	remoteslot = ExecInitExtraTupleSlot(estate,
+										RelationGetDescr(rel->localrel),
+										&TTSOpsVirtual);
+
+	/* Process and store remote tuple in the slot */
+	oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
+	slot_store_data(remoteslot, rel, &newtup);
+	slot_fill_defaults(rel, estate, remoteslot);
+	MemoryContextSwitchTo(oldctx);
+
+	/* For a partitioned table, insert the tuple into a partition. */
+	if (rel->localrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+		apply_handle_tuple_routing(edata,
+								   remoteslot, NULL, CMD_INSERT);
+	else
+		apply_handle_insert_internal(edata, edata->targetRelInfo,
+									 remoteslot);
+
+	finish_edata(edata);
+
+	logicalrep_rel_close(rel, NoLock);
+
+	end_replication_step();
+}
+
+/*
+ * Workhorse for apply_handle_insert()
+ * relinfo is for the relation we're actually inserting into
+ * (could be a child partition of edata->targetRelInfo)
+ */
+static void
+apply_handle_insert_internal(ApplyExecutionData *edata,
+							 ResultRelInfo *relinfo,
+							 TupleTableSlot *remoteslot)
+{
+	EState	   *estate = edata->estate;
+
+	/* We must open indexes here. */
+	ExecOpenIndices(relinfo, false);
+
+	/* Do the insert. */
+	ExecSimpleRelationInsert(relinfo, estate, remoteslot);
+
+	/* Cleanup. */
+	ExecCloseIndices(relinfo);
+}
+
+/*
+ * Check if the logical replication relation is updatable and throw
+ * appropriate error if it isn't.
+ */
+static void
+check_relation_updatable(LogicalRepRelMapEntry *rel)
+{
+	/*
+	 * For partitioned tables, we only need to care if the target partition is
+	 * updatable (aka has PK or RI defined for it).
+	 */
+	if (rel->localrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+		return;
+
+	/* Updatable, no error. */
+	if (rel->updatable)
+		return;
+
+	/*
+	 * We are in error mode so it's fine this is somewhat slow. It's better to
+	 * give user correct error.
+	 */
+	if (OidIsValid(GetRelationIdentityOrPK(rel->localrel)))
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("publisher did not send replica identity column "
+						"expected by the logical replication target relation \"%s.%s\"",
+						rel->remoterel.nspname, rel->remoterel.relname)));
+	}
+
+	ereport(ERROR,
+			(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+			 errmsg("logical replication target relation \"%s.%s\" has "
+					"neither REPLICA IDENTITY index nor PRIMARY "
+					"KEY and published relation does not have "
+					"REPLICA IDENTITY FULL",
+					rel->remoterel.nspname, rel->remoterel.relname)));
+}
+
+/*
+ * Handle UPDATE message.
+ *
+ * TODO: FDW support
+ */
+static void
+apply_handle_update(StringInfo s)
+{
+	LogicalRepRelMapEntry *rel;
+	LogicalRepRelId relid;
+	ApplyExecutionData *edata;
+	EState	   *estate;
+	LogicalRepTupleData oldtup;
+	LogicalRepTupleData newtup;
+	bool		has_oldtup;
+	TupleTableSlot *remoteslot;
+	RangeTblEntry *target_rte;
+	MemoryContext oldctx;
+
+	if (handle_streamed_transaction(LOGICAL_REP_MSG_UPDATE, s))
+		return;
+
+	begin_replication_step();
+
+	relid = logicalrep_read_update(s, &has_oldtup, &oldtup,
+								   &newtup);
+	rel = logicalrep_rel_open(relid, RowExclusiveLock);
+	if (!should_apply_changes_for_rel(rel))
+	{
+		/*
+		 * The relation can't become interesting in the middle of the
+		 * transaction so it's safe to unlock it.
+		 */
+		logicalrep_rel_close(rel, RowExclusiveLock);
+		end_replication_step();
+		return;
+	}
+
+	/* Check if we can do the update. */
+	check_relation_updatable(rel);
+
+	/* Initialize the executor state. */
+	edata = create_edata_for_relation(rel);
+	estate = edata->estate;
+	remoteslot = ExecInitExtraTupleSlot(estate,
+										RelationGetDescr(rel->localrel),
+										&TTSOpsVirtual);
+
+	/*
+	 * Populate updatedCols so that per-column triggers can fire, and so
+	 * executor can correctly pass down indexUnchanged hint.  This could
+	 * include more columns than were actually changed on the publisher
+	 * because the logical replication protocol doesn't contain that
+	 * information.  But it would for example exclude columns that only exist
+	 * on the subscriber, since we are not touching those.
+	 */
+	target_rte = list_nth(estate->es_range_table, 0);
+	for (int i = 0; i < remoteslot->tts_tupleDescriptor->natts; i++)
+	{
+		Form_pg_attribute att = TupleDescAttr(remoteslot->tts_tupleDescriptor, i);
+		int			remoteattnum = rel->attrmap->attnums[i];
+
+		if (!att->attisdropped && remoteattnum >= 0)
+		{
+			Assert(remoteattnum < newtup.ncols);
+			if (newtup.colstatus[remoteattnum] != LOGICALREP_COLUMN_UNCHANGED)
+				target_rte->updatedCols =
+					bms_add_member(target_rte->updatedCols,
+								   i + 1 - FirstLowInvalidHeapAttributeNumber);
+		}
+	}
+
+	/* Also populate extraUpdatedCols, in case we have generated columns */
+	fill_extraUpdatedCols(target_rte, rel->localrel);
+
+	/* Build the search tuple. */
+	oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
+	slot_store_data(remoteslot, rel,
+					has_oldtup ? &oldtup : &newtup);
+	MemoryContextSwitchTo(oldctx);
+
+	/* For a partitioned table, apply update to correct partition. */
+	if (rel->localrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+		apply_handle_tuple_routing(edata,
+								   remoteslot, &newtup, CMD_UPDATE);
+	else
+		apply_handle_update_internal(edata, edata->targetRelInfo,
+									 remoteslot, &newtup);
+
+	finish_edata(edata);
+
+	logicalrep_rel_close(rel, NoLock);
+
+	end_replication_step();
+}
+
+/*
+ * Workhorse for apply_handle_update()
+ * relinfo is for the relation we're actually updating in
+ * (could be a child partition of edata->targetRelInfo)
+ */
+static void
+apply_handle_update_internal(ApplyExecutionData *edata,
+							 ResultRelInfo *relinfo,
+							 TupleTableSlot *remoteslot,
+							 LogicalRepTupleData *newtup)
+{
+	EState	   *estate = edata->estate;
+	LogicalRepRelMapEntry *relmapentry = edata->targetRel;
+	Relation	localrel = relinfo->ri_RelationDesc;
+	EPQState	epqstate;
+	TupleTableSlot *localslot;
+	bool		found;
+	MemoryContext oldctx;
+
+	EvalPlanQualInit(&epqstate, estate, NULL, NIL, -1);
+	ExecOpenIndices(relinfo, false);
+
+	found = FindReplTupleInLocalRel(estate, localrel,
+									&relmapentry->remoterel,
+									remoteslot, &localslot);
+	ExecClearTuple(remoteslot);
+
+	/*
+	 * Tuple found.
+	 *
+	 * Note this will fail if there are other conflicting unique indexes.
+	 */
+	if (found)
+	{
+		/* Process and store remote tuple in the slot */
+		oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
+		slot_modify_data(remoteslot, localslot, relmapentry, newtup);
+		MemoryContextSwitchTo(oldctx);
+
+		EvalPlanQualSetSlot(&epqstate, remoteslot);
+
+		/* Do the actual update. */
+		ExecSimpleRelationUpdate(relinfo, estate, &epqstate, localslot,
+								 remoteslot);
+	}
+	else
+	{
+		/*
+		 * The tuple to be updated could not be found.  Do nothing except for
+		 * emitting a log message.
+		 *
+		 * XXX should this be promoted to ereport(LOG) perhaps?
+		 */
+		elog(DEBUG1,
+			 "logical replication did not find row to be updated "
+			 "in replication target relation \"%s\"",
+			 RelationGetRelationName(localrel));
+	}
+
+	/* Cleanup. */
+	ExecCloseIndices(relinfo);
+	EvalPlanQualEnd(&epqstate);
+}
+
+/*
+ * Handle DELETE message.
+ *
+ * TODO: FDW support
+ */
+static void
+apply_handle_delete(StringInfo s)
+{
+	LogicalRepRelMapEntry *rel;
+	LogicalRepTupleData oldtup;
+	LogicalRepRelId relid;
+	ApplyExecutionData *edata;
+	EState	   *estate;
+	TupleTableSlot *remoteslot;
+	MemoryContext oldctx;
+
+	if (handle_streamed_transaction(LOGICAL_REP_MSG_DELETE, s))
+		return;
+
+	begin_replication_step();
+
+	relid = logicalrep_read_delete(s, &oldtup);
+	rel = logicalrep_rel_open(relid, RowExclusiveLock);
+	if (!should_apply_changes_for_rel(rel))
+	{
+		/*
+		 * The relation can't become interesting in the middle of the
+		 * transaction so it's safe to unlock it.
+		 */
+		logicalrep_rel_close(rel, RowExclusiveLock);
+		end_replication_step();
+		return;
+	}
+
+	/* Check if we can do the delete. */
+	check_relation_updatable(rel);
+
+	/* Initialize the executor state. */
+	edata = create_edata_for_relation(rel);
+	estate = edata->estate;
+	remoteslot = ExecInitExtraTupleSlot(estate,
+										RelationGetDescr(rel->localrel),
+										&TTSOpsVirtual);
+
+	/* Build the search tuple. */
+	oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
+	slot_store_data(remoteslot, rel, &oldtup);
+	MemoryContextSwitchTo(oldctx);
+
+	/* For a partitioned table, apply delete to correct partition. */
+	if (rel->localrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+		apply_handle_tuple_routing(edata,
+								   remoteslot, NULL, CMD_DELETE);
+	else
+		apply_handle_delete_internal(edata, edata->targetRelInfo,
+									 remoteslot);
+
+	finish_edata(edata);
+
+	logicalrep_rel_close(rel, NoLock);
+
+	end_replication_step();
+}
+
+/*
+ * Workhorse for apply_handle_delete()
+ * relinfo is for the relation we're actually deleting from
+ * (could be a child partition of edata->targetRelInfo)
+ */
+static void
+apply_handle_delete_internal(ApplyExecutionData *edata,
+							 ResultRelInfo *relinfo,
+							 TupleTableSlot *remoteslot)
+{
+	EState	   *estate = edata->estate;
+	Relation	localrel = relinfo->ri_RelationDesc;
+	LogicalRepRelation *remoterel = &edata->targetRel->remoterel;
+	EPQState	epqstate;
+	TupleTableSlot *localslot;
+	bool		found;
+
+	EvalPlanQualInit(&epqstate, estate, NULL, NIL, -1);
+	ExecOpenIndices(relinfo, false);
+
+	found = FindReplTupleInLocalRel(estate, localrel, remoterel,
+									remoteslot, &localslot);
+
+	/* If found delete it. */
+	if (found)
+	{
+		EvalPlanQualSetSlot(&epqstate, localslot);
+
+		/* Do the actual delete. */
+		ExecSimpleRelationDelete(relinfo, estate, &epqstate, localslot);
+	}
+	else
+	{
+		/*
+		 * The tuple to be deleted could not be found.  Do nothing except for
+		 * emitting a log message.
+		 *
+		 * XXX should this be promoted to ereport(LOG) perhaps?
+		 */
+		elog(DEBUG1,
+			 "logical replication did not find row to be deleted "
+			 "in replication target relation \"%s\"",
+			 RelationGetRelationName(localrel));
+	}
+
+	/* Cleanup. */
+	ExecCloseIndices(relinfo);
+	EvalPlanQualEnd(&epqstate);
+}
+
+/*
+ * Try to find a tuple received from the publication side (in 'remoteslot') in
+ * the corresponding local relation using either replica identity index,
+ * primary key or if needed, sequential scan.
+ *
+ * Local tuple, if found, is returned in '*localslot'.
+ */
+static bool
+FindReplTupleInLocalRel(EState *estate, Relation localrel,
+						LogicalRepRelation *remoterel,
+						TupleTableSlot *remoteslot,
+						TupleTableSlot **localslot)
+{
+	Oid			idxoid;
+	bool		found;
+
+	*localslot = table_slot_create(localrel, &estate->es_tupleTable);
+
+	idxoid = GetRelationIdentityOrPK(localrel);
+	Assert(OidIsValid(idxoid) ||
+		   (remoterel->replident == REPLICA_IDENTITY_FULL));
+
+	if (OidIsValid(idxoid))
+		found = RelationFindReplTupleByIndex(localrel, idxoid,
+											 LockTupleExclusive,
+											 remoteslot, *localslot);
+	else
+		found = RelationFindReplTupleSeq(localrel, LockTupleExclusive,
+										 remoteslot, *localslot);
+
+	return found;
+}
+
+/*
+ * This handles insert, update, delete on a partitioned table.
+ */
+static void
+apply_handle_tuple_routing(ApplyExecutionData *edata,
+						   TupleTableSlot *remoteslot,
+						   LogicalRepTupleData *newtup,
+						   CmdType operation)
+{
+	EState	   *estate = edata->estate;
+	LogicalRepRelMapEntry *relmapentry = edata->targetRel;
+	ResultRelInfo *relinfo = edata->targetRelInfo;
+	Relation	parentrel = relinfo->ri_RelationDesc;
+	ModifyTableState *mtstate;
+	PartitionTupleRouting *proute;
+	ResultRelInfo *partrelinfo;
+	Relation	partrel;
+	TupleTableSlot *remoteslot_part;
+	TupleConversionMap *map;
+	MemoryContext oldctx;
+	LogicalRepRelMapEntry *part_entry = NULL;
+	AttrMap    *attrmap = NULL;
+
+	/* ModifyTableState is needed for ExecFindPartition(). */
+	edata->mtstate = mtstate = makeNode(ModifyTableState);
+	mtstate->ps.plan = NULL;
+	mtstate->ps.state = estate;
+	mtstate->operation = operation;
+	mtstate->resultRelInfo = relinfo;
+
+	/* ... as is PartitionTupleRouting. */
+	edata->proute = proute = ExecSetupPartitionTupleRouting(estate, parentrel);
+
+	/*
+	 * Find the partition to which the "search tuple" belongs.
+	 */
+	Assert(remoteslot != NULL);
+	oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
+	partrelinfo = ExecFindPartition(mtstate, relinfo, proute,
+									remoteslot, estate);
+	Assert(partrelinfo != NULL);
+	partrel = partrelinfo->ri_RelationDesc;
+
+	/*
+	 * To perform any of the operations below, the tuple must match the
+	 * partition's rowtype. Convert if needed or just copy, using a dedicated
+	 * slot to store the tuple in any case.
+	 */
+	remoteslot_part = partrelinfo->ri_PartitionTupleSlot;
+	if (remoteslot_part == NULL)
+		remoteslot_part = table_slot_create(partrel, &estate->es_tupleTable);
+	map = partrelinfo->ri_RootToPartitionMap;
+	if (map != NULL)
+	{
+		attrmap = map->attrMap;
+		remoteslot_part = execute_attr_map_slot(attrmap, remoteslot,
+												remoteslot_part);
+	}
+	else
+	{
+		remoteslot_part = ExecCopySlot(remoteslot_part, remoteslot);
+		slot_getallattrs(remoteslot_part);
+	}
+	MemoryContextSwitchTo(oldctx);
+
+	/* Check if we can do the update or delete on the leaf partition. */
+	if (operation == CMD_UPDATE || operation == CMD_DELETE)
+	{
+		part_entry = logicalrep_partition_open(relmapentry, partrel,
+											   attrmap);
+		check_relation_updatable(part_entry);
+	}
+
+	switch (operation)
+	{
+		case CMD_INSERT:
+			apply_handle_insert_internal(edata, partrelinfo,
+										 remoteslot_part);
+			break;
+
+		case CMD_DELETE:
+			apply_handle_delete_internal(edata, partrelinfo,
+										 remoteslot_part);
+			break;
+
+		case CMD_UPDATE:
+
+			/*
+			 * For UPDATE, depending on whether or not the updated tuple
+			 * satisfies the partition's constraint, perform a simple UPDATE
+			 * of the partition or move the updated tuple into a different
+			 * suitable partition.
+			 */
+			{
+				TupleTableSlot *localslot;
+				ResultRelInfo *partrelinfo_new;
+				bool		found;
+
+				/* Get the matching local tuple from the partition. */
+				found = FindReplTupleInLocalRel(estate, partrel,
+												&part_entry->remoterel,
+												remoteslot_part, &localslot);
+				if (!found)
+				{
+					/*
+					 * The tuple to be updated could not be found.  Do nothing
+					 * except for emitting a log message.
+					 *
+					 * XXX should this be promoted to ereport(LOG) perhaps?
+					 */
+					elog(DEBUG1,
+						 "logical replication did not find row to be updated "
+						 "in replication target relation's partition \"%s\"",
+						 RelationGetRelationName(partrel));
+					return;
+				}
+
+				/*
+				 * Apply the update to the local tuple, putting the result in
+				 * remoteslot_part.
+				 */
+				oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
+				slot_modify_data(remoteslot_part, localslot, part_entry,
+								 newtup);
+				MemoryContextSwitchTo(oldctx);
+
+				/*
+				 * Does the updated tuple still satisfy the current
+				 * partition's constraint?
+				 */
+				if (!partrel->rd_rel->relispartition ||
+					ExecPartitionCheck(partrelinfo, remoteslot_part, estate,
+									   false))
+				{
+					/*
+					 * Yes, so simply UPDATE the partition.  We don't call
+					 * apply_handle_update_internal() here, which would
+					 * normally do the following work, to avoid repeating some
+					 * work already done above to find the local tuple in the
+					 * partition.
+					 */
+					EPQState	epqstate;
+
+					EvalPlanQualInit(&epqstate, estate, NULL, NIL, -1);
+					ExecOpenIndices(partrelinfo, false);
+
+					EvalPlanQualSetSlot(&epqstate, remoteslot_part);
+					ExecSimpleRelationUpdate(partrelinfo, estate, &epqstate,
+											 localslot, remoteslot_part);
+					ExecCloseIndices(partrelinfo);
+					EvalPlanQualEnd(&epqstate);
+				}
+				else
+				{
+					/* Move the tuple into the new partition. */
+
+					/*
+					 * New partition will be found using tuple routing, which
+					 * can only occur via the parent table.  We might need to
+					 * convert the tuple to the parent's rowtype.  Note that
+					 * this is the tuple found in the partition, not the
+					 * original search tuple received by this function.
+					 */
+					if (map)
+					{
+						TupleConversionMap *PartitionToRootMap =
+						convert_tuples_by_name(RelationGetDescr(partrel),
+											   RelationGetDescr(parentrel));
+
+						remoteslot =
+							execute_attr_map_slot(PartitionToRootMap->attrMap,
+												  remoteslot_part, remoteslot);
+					}
+					else
+					{
+						remoteslot = ExecCopySlot(remoteslot, remoteslot_part);
+						slot_getallattrs(remoteslot);
+					}
+
+
+					/* Find the new partition. */
+					oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
+					partrelinfo_new = ExecFindPartition(mtstate, relinfo,
+														proute, remoteslot,
+														estate);
+					MemoryContextSwitchTo(oldctx);
+					Assert(partrelinfo_new != partrelinfo);
+
+					/* DELETE old tuple found in the old partition. */
+					apply_handle_delete_internal(edata, partrelinfo,
+												 localslot);
+
+					/* INSERT new tuple into the new partition. */
+
+					/*
+					 * Convert the replacement tuple to match the destination
+					 * partition rowtype.
+					 */
+					oldctx = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
+					partrel = partrelinfo_new->ri_RelationDesc;
+					remoteslot_part = partrelinfo_new->ri_PartitionTupleSlot;
+					if (remoteslot_part == NULL)
+						remoteslot_part = table_slot_create(partrel,
+															&estate->es_tupleTable);
+					map = partrelinfo_new->ri_RootToPartitionMap;
+					if (map != NULL)
+					{
+						remoteslot_part = execute_attr_map_slot(map->attrMap,
+																remoteslot,
+																remoteslot_part);
+					}
+					else
+					{
+						remoteslot_part = ExecCopySlot(remoteslot_part,
+													   remoteslot);
+						slot_getallattrs(remoteslot);
+					}
+					MemoryContextSwitchTo(oldctx);
+					apply_handle_insert_internal(edata, partrelinfo_new,
+												 remoteslot_part);
+				}
+			}
+			break;
+
+		default:
+			elog(ERROR, "unrecognized CmdType: %d", (int) operation);
+			break;
+	}
+}
+
+/*
+ * Handle TRUNCATE message.
+ *
+ * TODO: FDW support
+ */
+static void
+apply_handle_truncate(StringInfo s)
+{
+	bool		cascade = false;
+	bool		restart_seqs = false;
+	List	   *remote_relids = NIL;
+	List	   *remote_rels = NIL;
+	List	   *rels = NIL;
+	List	   *part_rels = NIL;
+	List	   *relids = NIL;
+	List	   *relids_logged = NIL;
+	ListCell   *lc;
+	LOCKMODE	lockmode = AccessExclusiveLock;
+
+	if (handle_streamed_transaction(LOGICAL_REP_MSG_TRUNCATE, s))
+		return;
+
+	begin_replication_step();
+
+	remote_relids = logicalrep_read_truncate(s, &cascade, &restart_seqs);
+
+	foreach(lc, remote_relids)
+	{
+		LogicalRepRelId relid = lfirst_oid(lc);
+		LogicalRepRelMapEntry *rel;
+
+		rel = logicalrep_rel_open(relid, lockmode);
+		if (!should_apply_changes_for_rel(rel))
+		{
+			/*
+			 * The relation can't become interesting in the middle of the
+			 * transaction so it's safe to unlock it.
+			 */
+			logicalrep_rel_close(rel, lockmode);
+			continue;
+		}
+
+		remote_rels = lappend(remote_rels, rel);
+		rels = lappend(rels, rel->localrel);
+		relids = lappend_oid(relids, rel->localreloid);
+		if (RelationIsLogicallyLogged(rel->localrel))
+			relids_logged = lappend_oid(relids_logged, rel->localreloid);
+
+		/*
+		 * Truncate partitions if we got a message to truncate a partitioned
+		 * table.
+		 */
+		if (rel->localrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+		{
+			ListCell   *child;
+			List	   *children = find_all_inheritors(rel->localreloid,
+													   lockmode,
+													   NULL);
+
+			foreach(child, children)
+			{
+				Oid			childrelid = lfirst_oid(child);
+				Relation	childrel;
+
+				if (list_member_oid(relids, childrelid))
+					continue;
+
+				/* find_all_inheritors already got lock */
+				childrel = table_open(childrelid, NoLock);
+
+				/*
+				 * Ignore temp tables of other backends.  See similar code in
+				 * ExecuteTruncate().
+				 */
+				if (RELATION_IS_OTHER_TEMP(childrel))
+				{
+					table_close(childrel, lockmode);
+					continue;
+				}
+
+				rels = lappend(rels, childrel);
+				part_rels = lappend(part_rels, childrel);
+				relids = lappend_oid(relids, childrelid);
+				/* Log this relation only if needed for logical decoding */
+				if (RelationIsLogicallyLogged(childrel))
+					relids_logged = lappend_oid(relids_logged, childrelid);
+			}
+		}
+	}
+
+	/*
+	 * Even if we used CASCADE on the upstream primary we explicitly default
+	 * to replaying changes without further cascading. This might be later
+	 * changeable with a user specified option.
+	 */
+	ExecuteTruncateGuts(rels,
+						relids,
+						relids_logged,
+						DROP_RESTRICT,
+						restart_seqs);
+	foreach(lc, remote_rels)
+	{
+		LogicalRepRelMapEntry *rel = lfirst(lc);
+
+		logicalrep_rel_close(rel, NoLock);
+	}
+	foreach(lc, part_rels)
+	{
+		Relation	rel = lfirst(lc);
+
+		table_close(rel, NoLock);
+	}
+
+	end_replication_step();
+}
+
+
+/*
+ * Logical replication protocol message dispatcher.
+ */
+static void
+apply_dispatch(StringInfo s)
+{
+	LogicalRepMsgType action = pq_getmsgbyte(s);
+
+	switch (action)
+	{
+		case LOGICAL_REP_MSG_BEGIN:
+			apply_handle_begin(s);
+			return;
+
+		case LOGICAL_REP_MSG_COMMIT:
+			apply_handle_commit(s);
+			return;
+
+		case LOGICAL_REP_MSG_INSERT:
+			apply_handle_insert(s);
+			return;
+
+		case LOGICAL_REP_MSG_UPDATE:
+			apply_handle_update(s);
+			return;
+
+		case LOGICAL_REP_MSG_DELETE:
+			apply_handle_delete(s);
+			return;
+
+		case LOGICAL_REP_MSG_TRUNCATE:
+			apply_handle_truncate(s);
+			return;
+
+		case LOGICAL_REP_MSG_RELATION:
+			apply_handle_relation(s);
+			return;
+
+		case LOGICAL_REP_MSG_TYPE:
+			apply_handle_type(s);
+			return;
+
+		case LOGICAL_REP_MSG_ORIGIN:
+			apply_handle_origin(s);
+			return;
+
+		case LOGICAL_REP_MSG_MESSAGE:
+
+			/*
+			 * Logical replication does not use generic logical messages yet.
+			 * Although, it could be used by other applications that use this
+			 * output plugin.
+			 */
+			return;
+
+		case LOGICAL_REP_MSG_STREAM_START:
+			apply_handle_stream_start(s);
+			return;
+
+		case LOGICAL_REP_MSG_STREAM_END:
+			apply_handle_stream_stop(s);
+			return;
+
+		case LOGICAL_REP_MSG_STREAM_ABORT:
+			apply_handle_stream_abort(s);
+			return;
+
+		case LOGICAL_REP_MSG_STREAM_COMMIT:
+			apply_handle_stream_commit(s);
+			return;
+	}
+
+	ereport(ERROR,
+			(errcode(ERRCODE_PROTOCOL_VIOLATION),
+			 errmsg_internal("invalid logical replication message type \"%c\"",
+							 action)));
+}
+
+/*
+ * Figure out which write/flush positions to report to the walsender process.
+ *
+ * We can't simply report back the last LSN the walsender sent us because the
+ * local transaction might not yet be flushed to disk locally. Instead we
+ * build a list that associates local with remote LSNs for every commit. When
+ * reporting back the flush position to the sender we iterate that list and
+ * check which entries on it are already locally flushed. Those we can report
+ * as having been flushed.
+ *
+ * The have_pending_txes is true if there are outstanding transactions that
+ * need to be flushed.
+ */
+static void
+get_flush_position(XLogRecPtr *write, XLogRecPtr *flush,
+				   bool *have_pending_txes)
+{
+	dlist_mutable_iter iter;
+	XLogRecPtr	local_flush = GetFlushRecPtr();
+
+	*write = InvalidXLogRecPtr;
+	*flush = InvalidXLogRecPtr;
+
+	dlist_foreach_modify(iter, &lsn_mapping)
+	{
+		FlushPosition *pos =
+		dlist_container(FlushPosition, node, iter.cur);
+
+		*write = pos->remote_end;
+
+		if (pos->local_end <= local_flush)
+		{
+			*flush = pos->remote_end;
+			dlist_delete(iter.cur);
+			pfree(pos);
+		}
+		else
+		{
+			/*
+			 * Don't want to uselessly iterate over the rest of the list which
+			 * could potentially be long. Instead get the last element and
+			 * grab the write position from there.
+			 */
+			pos = dlist_tail_element(FlushPosition, node,
+									 &lsn_mapping);
+			*write = pos->remote_end;
+			*have_pending_txes = true;
+			return;
+		}
+	}
+
+	*have_pending_txes = !dlist_is_empty(&lsn_mapping);
+}
+
+/*
+ * Store current remote/local lsn pair in the tracking list.
+ */
+static void
+store_flush_position(XLogRecPtr remote_lsn)
+{
+	FlushPosition *flushpos;
+
+	/* Need to do this in permanent context */
+	MemoryContextSwitchTo(ApplyContext);
+
+	/* Track commit lsn  */
+	flushpos = (FlushPosition *) palloc(sizeof(FlushPosition));
+	flushpos->local_end = XactLastCommitEnd;
+	flushpos->remote_end = remote_lsn;
+
+	dlist_push_tail(&lsn_mapping, &flushpos->node);
+	MemoryContextSwitchTo(ApplyMessageContext);
+}
+
+
+/* Update statistics of the worker. */
+static void
+UpdateWorkerStats(XLogRecPtr last_lsn, TimestampTz send_time, bool reply)
+{
+	MyLogicalRepWorker->last_lsn = last_lsn;
+	MyLogicalRepWorker->last_send_time = send_time;
+	MyLogicalRepWorker->last_recv_time = GetCurrentTimestamp();
+	if (reply)
+	{
+		MyLogicalRepWorker->reply_lsn = last_lsn;
+		MyLogicalRepWorker->reply_time = send_time;
+	}
+}
+
+/*
+ * Apply main loop.
+ */
+static void
+LogicalRepApplyLoop(XLogRecPtr last_received)
+{
+	TimestampTz last_recv_timestamp = GetCurrentTimestamp();
+	bool		ping_sent = false;
+	TimeLineID	tli;
+
+	/*
+	 * Init the ApplyMessageContext which we clean up after each replication
+	 * protocol message.
+	 */
+	ApplyMessageContext = AllocSetContextCreate(ApplyContext,
+												"ApplyMessageContext",
+												ALLOCSET_DEFAULT_SIZES);
+
+	/*
+	 * This memory context is used for per-stream data when the streaming mode
+	 * is enabled. This context is reset on each stream stop.
+	 */
+	LogicalStreamingContext = AllocSetContextCreate(ApplyContext,
+													"LogicalStreamingContext",
+													ALLOCSET_DEFAULT_SIZES);
+
+	/* mark as idle, before starting to loop */
+	pgstat_report_activity(STATE_IDLE, NULL);
+
+	/* This outer loop iterates once per wait. */
+	for (;;)
+	{
+		pgsocket	fd = PGINVALID_SOCKET;
+		int			rc;
+		int			len;
+		char	   *buf = NULL;
+		bool		endofstream = false;
+		long		wait_time;
+
+		CHECK_FOR_INTERRUPTS();
+
+		MemoryContextSwitchTo(ApplyMessageContext);
+
+		len = walrcv_receive(LogRepWorkerWalRcvConn, &buf, &fd);
+
+		if (len != 0)
+		{
+			/* Loop to process all available data (without blocking). */
+			for (;;)
+			{
+				CHECK_FOR_INTERRUPTS();
+
+				if (len == 0)
+				{
+					break;
+				}
+				else if (len < 0)
+				{
+					ereport(LOG,
+							(errmsg("data stream from publisher has ended")));
+					endofstream = true;
+					break;
+				}
+				else
+				{
+					int			c;
+					StringInfoData s;
+
+					/* Reset timeout. */
+					last_recv_timestamp = GetCurrentTimestamp();
+					ping_sent = false;
+
+					/* Ensure we are reading the data into our memory context. */
+					MemoryContextSwitchTo(ApplyMessageContext);
+
+					s.data = buf;
+					s.len = len;
+					s.cursor = 0;
+					s.maxlen = -1;
+
+					c = pq_getmsgbyte(&s);
+
+					if (c == 'w')
+					{
+						XLogRecPtr	start_lsn;
+						XLogRecPtr	end_lsn;
+						TimestampTz send_time;
+
+						start_lsn = pq_getmsgint64(&s);
+						end_lsn = pq_getmsgint64(&s);
+						send_time = pq_getmsgint64(&s);
+
+						if (last_received < start_lsn)
+							last_received = start_lsn;
+
+						if (last_received < end_lsn)
+							last_received = end_lsn;
+
+						UpdateWorkerStats(last_received, send_time, false);
+
+						apply_dispatch(&s);
+					}
+					else if (c == 'k')
+					{
+						XLogRecPtr	end_lsn;
+						TimestampTz timestamp;
+						bool		reply_requested;
+
+						end_lsn = pq_getmsgint64(&s);
+						timestamp = pq_getmsgint64(&s);
+						reply_requested = pq_getmsgbyte(&s);
+
+						if (last_received < end_lsn)
+							last_received = end_lsn;
+
+						send_feedback(last_received, reply_requested, false);
+						UpdateWorkerStats(last_received, timestamp, true);
+					}
+					/* other message types are purposefully ignored */
+
+					MemoryContextReset(ApplyMessageContext);
+				}
+
+				len = walrcv_receive(LogRepWorkerWalRcvConn, &buf, &fd);
+			}
+		}
+
+		/* confirm all writes so far */
+		send_feedback(last_received, false, false);
+
+		if (!in_remote_transaction && !in_streamed_transaction)
+		{
+			/*
+			 * If we didn't get any transactions for a while there might be
+			 * unconsumed invalidation messages in the queue, consume them
+			 * now.
+			 */
+			AcceptInvalidationMessages();
+			maybe_reread_subscription();
+
+			/* Process any table synchronization changes. */
+			process_syncing_tables(last_received);
+		}
+
+		/* Cleanup the memory. */
+		MemoryContextResetAndDeleteChildren(ApplyMessageContext);
+		MemoryContextSwitchTo(TopMemoryContext);
+
+		/* Check if we need to exit the streaming loop. */
+		if (endofstream)
+			break;
+
+		/*
+		 * Wait for more data or latch.  If we have unflushed transactions,
+		 * wake up after WalWriterDelay to see if they've been flushed yet (in
+		 * which case we should send a feedback message).  Otherwise, there's
+		 * no particular urgency about waking up unless we get data or a
+		 * signal.
+		 */
+		if (!dlist_is_empty(&lsn_mapping))
+			wait_time = WalWriterDelay;
+		else
+			wait_time = NAPTIME_PER_CYCLE;
+
+		rc = WaitLatchOrSocket(MyLatch,
+							   WL_SOCKET_READABLE | WL_LATCH_SET |
+							   WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+							   fd, wait_time,
+							   WAIT_EVENT_LOGICAL_APPLY_MAIN);
+
+		if (rc & WL_LATCH_SET)
+		{
+			ResetLatch(MyLatch);
+			CHECK_FOR_INTERRUPTS();
+		}
+
+		if (ConfigReloadPending)
+		{
+			ConfigReloadPending = false;
+			ProcessConfigFile(PGC_SIGHUP);
+		}
+
+		if (rc & WL_TIMEOUT)
+		{
+			/*
+			 * We didn't receive anything new. If we haven't heard anything
+			 * from the server for more than wal_receiver_timeout / 2, ping
+			 * the server. Also, if it's been longer than
+			 * wal_receiver_status_interval since the last update we sent,
+			 * send a status update to the primary anyway, to report any
+			 * progress in applying WAL.
+			 */
+			bool		requestReply = false;
+
+			/*
+			 * Check if time since last receive from primary has reached the
+			 * configured limit.
+			 */
+			if (wal_receiver_timeout > 0)
+			{
+				TimestampTz now = GetCurrentTimestamp();
+				TimestampTz timeout;
+
+				timeout =
+					TimestampTzPlusMilliseconds(last_recv_timestamp,
+												wal_receiver_timeout);
+
+				if (now >= timeout)
+					ereport(ERROR,
+							(errcode(ERRCODE_CONNECTION_FAILURE),
+							 errmsg("terminating logical replication worker due to timeout")));
+
+				/* Check to see if it's time for a ping. */
+				if (!ping_sent)
+				{
+					timeout = TimestampTzPlusMilliseconds(last_recv_timestamp,
+														  (wal_receiver_timeout / 2));
+					if (now >= timeout)
+					{
+						requestReply = true;
+						ping_sent = true;
+					}
+				}
+			}
+
+			send_feedback(last_received, requestReply, requestReply);
+		}
+	}
+
+	/* All done */
+	walrcv_endstreaming(LogRepWorkerWalRcvConn, &tli);
+}
+
+/*
+ * Send a Standby Status Update message to server.
+ *
+ * 'recvpos' is the latest LSN we've received data to, force is set if we need
+ * to send a response to avoid timeouts.
+ */
+static void
+send_feedback(XLogRecPtr recvpos, bool force, bool requestReply)
+{
+	static StringInfo reply_message = NULL;
+	static TimestampTz send_time = 0;
+
+	static XLogRecPtr last_recvpos = InvalidXLogRecPtr;
+	static XLogRecPtr last_writepos = InvalidXLogRecPtr;
+	static XLogRecPtr last_flushpos = InvalidXLogRecPtr;
+
+	XLogRecPtr	writepos;
+	XLogRecPtr	flushpos;
+	TimestampTz now;
+	bool		have_pending_txes;
+
+	/*
+	 * If the user doesn't want status to be reported to the publisher, be
+	 * sure to exit before doing anything at all.
+	 */
+	if (!force && wal_receiver_status_interval <= 0)
+		return;
+
+	/* It's legal to not pass a recvpos */
+	if (recvpos < last_recvpos)
+		recvpos = last_recvpos;
+
+	get_flush_position(&writepos, &flushpos, &have_pending_txes);
+
+	/*
+	 * No outstanding transactions to flush, we can report the latest received
+	 * position. This is important for synchronous replication.
+	 */
+	if (!have_pending_txes)
+		flushpos = writepos = recvpos;
+
+	if (writepos < last_writepos)
+		writepos = last_writepos;
+
+	if (flushpos < last_flushpos)
+		flushpos = last_flushpos;
+
+	now = GetCurrentTimestamp();
+
+	/* if we've already reported everything we're good */
+	if (!force &&
+		writepos == last_writepos &&
+		flushpos == last_flushpos &&
+		!TimestampDifferenceExceeds(send_time, now,
+									wal_receiver_status_interval * 1000))
+		return;
+	send_time = now;
+
+	if (!reply_message)
+	{
+		MemoryContext oldctx = MemoryContextSwitchTo(ApplyContext);
+
+		reply_message = makeStringInfo();
+		MemoryContextSwitchTo(oldctx);
+	}
+	else
+		resetStringInfo(reply_message);
+
+	pq_sendbyte(reply_message, 'r');
+	pq_sendint64(reply_message, recvpos);	/* write */
+	pq_sendint64(reply_message, flushpos);	/* flush */
+	pq_sendint64(reply_message, writepos);	/* apply */
+	pq_sendint64(reply_message, now);	/* sendTime */
+	pq_sendbyte(reply_message, requestReply);	/* replyRequested */
+
+	elog(DEBUG2, "sending feedback (force %d) to recv %X/%X, write %X/%X, flush %X/%X",
+		 force,
+		 LSN_FORMAT_ARGS(recvpos),
+		 LSN_FORMAT_ARGS(writepos),
+		 LSN_FORMAT_ARGS(flushpos));
+
+	walrcv_send(LogRepWorkerWalRcvConn,
+				reply_message->data, reply_message->len);
+
+	if (recvpos > last_recvpos)
+		last_recvpos = recvpos;
+	if (writepos > last_writepos)
+		last_writepos = writepos;
+	if (flushpos > last_flushpos)
+		last_flushpos = flushpos;
+}
+
+/*
+ * Reread subscription info if needed. Most changes will be exit.
+ */
+static void
+maybe_reread_subscription(void)
+{
+	MemoryContext oldctx;
+	Subscription *newsub;
+	bool		started_tx = false;
+
+	/* When cache state is valid there is nothing to do here. */
+	if (MySubscriptionValid)
+		return;
+
+	/* This function might be called inside or outside of transaction. */
+	if (!IsTransactionState())
+	{
+		StartTransactionCommand();
+		started_tx = true;
+	}
+
+	/* Ensure allocations in permanent context. */
+	oldctx = MemoryContextSwitchTo(ApplyContext);
+
+	newsub = GetSubscription(MyLogicalRepWorker->subid, true);
+
+	/*
+	 * Exit if the subscription was removed. This normally should not happen
+	 * as the worker gets killed during DROP SUBSCRIPTION.
+	 */
+	if (!newsub)
+	{
+		ereport(LOG,
+				(errmsg("logical replication apply worker for subscription \"%s\" will "
+						"stop because the subscription was removed",
+						MySubscription->name)));
+
+		proc_exit(0);
+	}
+
+	/*
+	 * Exit if the subscription was disabled. This normally should not happen
+	 * as the worker gets killed during ALTER SUBSCRIPTION ... DISABLE.
+	 */
+	if (!newsub->enabled)
+	{
+		ereport(LOG,
+				(errmsg("logical replication apply worker for subscription \"%s\" will "
+						"stop because the subscription was disabled",
+						MySubscription->name)));
+
+		proc_exit(0);
+	}
+
+	/* !slotname should never happen when enabled is true. */
+	Assert(newsub->slotname);
+
+	/*
+	 * Exit if any parameter that affects the remote connection was changed.
+	 * The launcher will start a new worker.
+	 */
+	if (strcmp(newsub->conninfo, MySubscription->conninfo) != 0 ||
+		strcmp(newsub->name, MySubscription->name) != 0 ||
+		strcmp(newsub->slotname, MySubscription->slotname) != 0 ||
+		newsub->binary != MySubscription->binary ||
+		newsub->stream != MySubscription->stream ||
+		!equal(newsub->publications, MySubscription->publications))
+	{
+		ereport(LOG,
+				(errmsg("logical replication apply worker for subscription \"%s\" will restart because of a parameter change",
+						MySubscription->name)));
+
+		proc_exit(0);
+	}
+
+	/* Check for other changes that should never happen too. */
+	if (newsub->dbid != MySubscription->dbid)
+	{
+		elog(ERROR, "subscription %u changed unexpectedly",
+			 MyLogicalRepWorker->subid);
+	}
+
+	/* Clean old subscription info and switch to new one. */
+	FreeSubscription(MySubscription);
+	MySubscription = newsub;
+
+	MemoryContextSwitchTo(oldctx);
+
+	/* Change synchronous commit according to the user's wishes */
+	SetConfigOption("synchronous_commit", MySubscription->synccommit,
+					PGC_BACKEND, PGC_S_OVERRIDE);
+
+	if (started_tx)
+		CommitTransactionCommand();
+
+	MySubscriptionValid = true;
+}
+
+/*
+ * Callback from subscription syscache invalidation.
+ */
+static void
+subscription_change_cb(Datum arg, int cacheid, uint32 hashvalue)
+{
+	MySubscriptionValid = false;
+}
+
+/*
+ * subxact_info_write
+ *	  Store information about subxacts for a toplevel transaction.
+ *
+ * For each subxact we store offset of it's first change in the main file.
+ * The file is always over-written as a whole.
+ *
+ * XXX We should only store subxacts that were not aborted yet.
+ */
+static void
+subxact_info_write(Oid subid, TransactionId xid)
+{
+	char		path[MAXPGPATH];
+	Size		len;
+	StreamXidHash *ent;
+	BufFile    *fd;
+
+	Assert(TransactionIdIsValid(xid));
+
+	/* Find the xid entry in the xidhash */
+	ent = (StreamXidHash *) hash_search(xidhash,
+										(void *) &xid,
+										HASH_FIND,
+										NULL);
+	/* By this time we must have created the transaction entry */
+	Assert(ent);
+
+	/*
+	 * If there is no subtransaction then nothing to do, but if already have
+	 * subxact file then delete that.
+	 */
+	if (subxact_data.nsubxacts == 0)
+	{
+		if (ent->subxact_fileset)
+		{
+			cleanup_subxact_info();
+			SharedFileSetDeleteAll(ent->subxact_fileset);
+			pfree(ent->subxact_fileset);
+			ent->subxact_fileset = NULL;
+		}
+		return;
+	}
+
+	subxact_filename(path, subid, xid);
+
+	/*
+	 * Create the subxact file if it not already created, otherwise open the
+	 * existing file.
+	 */
+	if (ent->subxact_fileset == NULL)
+	{
+		MemoryContext oldctx;
+
+		/*
+		 * We need to maintain shared fileset across multiple stream
+		 * start/stop calls.  So, need to allocate it in a persistent context.
+		 */
+		oldctx = MemoryContextSwitchTo(ApplyContext);
+		ent->subxact_fileset = palloc(sizeof(SharedFileSet));
+		SharedFileSetInit(ent->subxact_fileset, NULL);
+		MemoryContextSwitchTo(oldctx);
+
+		fd = BufFileCreateShared(ent->subxact_fileset, path);
+	}
+	else
+		fd = BufFileOpenShared(ent->subxact_fileset, path, O_RDWR);
+
+	len = sizeof(SubXactInfo) * subxact_data.nsubxacts;
+
+	/* Write the subxact count and subxact info */
+	BufFileWrite(fd, &subxact_data.nsubxacts, sizeof(subxact_data.nsubxacts));
+	BufFileWrite(fd, subxact_data.subxacts, len);
+
+	BufFileClose(fd);
+
+	/* free the memory allocated for subxact info */
+	cleanup_subxact_info();
+}
+
+/*
+ * subxact_info_read
+ *	  Restore information about subxacts of a streamed transaction.
+ *
+ * Read information about subxacts into the structure subxact_data that can be
+ * used later.
+ */
+static void
+subxact_info_read(Oid subid, TransactionId xid)
+{
+	char		path[MAXPGPATH];
+	Size		len;
+	BufFile    *fd;
+	StreamXidHash *ent;
+	MemoryContext oldctx;
+
+	Assert(!subxact_data.subxacts);
+	Assert(subxact_data.nsubxacts == 0);
+	Assert(subxact_data.nsubxacts_max == 0);
+
+	/* Find the stream xid entry in the xidhash */
+	ent = (StreamXidHash *) hash_search(xidhash,
+										(void *) &xid,
+										HASH_FIND,
+										NULL);
+	if (!ent)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("transaction %u not found in stream XID hash table",
+								 xid)));
+
+	/*
+	 * If subxact_fileset is not valid that mean we don't have any subxact
+	 * info
+	 */
+	if (ent->subxact_fileset == NULL)
+		return;
+
+	subxact_filename(path, subid, xid);
+
+	fd = BufFileOpenShared(ent->subxact_fileset, path, O_RDONLY);
+
+	/* read number of subxact items */
+	if (BufFileRead(fd, &subxact_data.nsubxacts,
+					sizeof(subxact_data.nsubxacts)) !=
+		sizeof(subxact_data.nsubxacts))
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not read from streaming transaction's subxact file \"%s\": %m",
+						path)));
+
+	len = sizeof(SubXactInfo) * subxact_data.nsubxacts;
+
+	/* we keep the maximum as a power of 2 */
+	subxact_data.nsubxacts_max = 1 << my_log2(subxact_data.nsubxacts);
+
+	/*
+	 * Allocate subxact information in the logical streaming context. We need
+	 * this information during the complete stream so that we can add the sub
+	 * transaction info to this. On stream stop we will flush this information
+	 * to the subxact file and reset the logical streaming context.
+	 */
+	oldctx = MemoryContextSwitchTo(LogicalStreamingContext);
+	subxact_data.subxacts = palloc(subxact_data.nsubxacts_max *
+								   sizeof(SubXactInfo));
+	MemoryContextSwitchTo(oldctx);
+
+	if ((len > 0) && ((BufFileRead(fd, subxact_data.subxacts, len)) != len))
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not read from streaming transaction's subxact file \"%s\": %m",
+						path)));
+
+	BufFileClose(fd);
+}
+
+/*
+ * subxact_info_add
+ *	  Add information about a subxact (offset in the main file).
+ */
+static void
+subxact_info_add(TransactionId xid)
+{
+	SubXactInfo *subxacts = subxact_data.subxacts;
+	int64		i;
+
+	/* We must have a valid top level stream xid and a stream fd. */
+	Assert(TransactionIdIsValid(stream_xid));
+	Assert(stream_fd != NULL);
+
+	/*
+	 * If the XID matches the toplevel transaction, we don't want to add it.
+	 */
+	if (stream_xid == xid)
+		return;
+
+	/*
+	 * In most cases we're checking the same subxact as we've already seen in
+	 * the last call, so make sure to ignore it (this change comes later).
+	 */
+	if (subxact_data.subxact_last == xid)
+		return;
+
+	/* OK, remember we're processing this XID. */
+	subxact_data.subxact_last = xid;
+
+	/*
+	 * Check if the transaction is already present in the array of subxact. We
+	 * intentionally scan the array from the tail, because we're likely adding
+	 * a change for the most recent subtransactions.
+	 *
+	 * XXX Can we rely on the subxact XIDs arriving in sorted order? That
+	 * would allow us to use binary search here.
+	 */
+	for (i = subxact_data.nsubxacts; i > 0; i--)
+	{
+		/* found, so we're done */
+		if (subxacts[i - 1].xid == xid)
+			return;
+	}
+
+	/* This is a new subxact, so we need to add it to the array. */
+	if (subxact_data.nsubxacts == 0)
+	{
+		MemoryContext oldctx;
+
+		subxact_data.nsubxacts_max = 128;
+
+		/*
+		 * Allocate this memory for subxacts in per-stream context, see
+		 * subxact_info_read.
+		 */
+		oldctx = MemoryContextSwitchTo(LogicalStreamingContext);
+		subxacts = palloc(subxact_data.nsubxacts_max * sizeof(SubXactInfo));
+		MemoryContextSwitchTo(oldctx);
+	}
+	else if (subxact_data.nsubxacts == subxact_data.nsubxacts_max)
+	{
+		subxact_data.nsubxacts_max *= 2;
+		subxacts = repalloc(subxacts,
+							subxact_data.nsubxacts_max * sizeof(SubXactInfo));
+	}
+
+	subxacts[subxact_data.nsubxacts].xid = xid;
+
+	/*
+	 * Get the current offset of the stream file and store it as offset of
+	 * this subxact.
+	 */
+	BufFileTell(stream_fd,
+				&subxacts[subxact_data.nsubxacts].fileno,
+				&subxacts[subxact_data.nsubxacts].offset);
+
+	subxact_data.nsubxacts++;
+	subxact_data.subxacts = subxacts;
+}
+
+/* format filename for file containing the info about subxacts */
+static inline void
+subxact_filename(char *path, Oid subid, TransactionId xid)
+{
+	snprintf(path, MAXPGPATH, "%u-%u.subxacts", subid, xid);
+}
+
+/* format filename for file containing serialized changes */
+static inline void
+changes_filename(char *path, Oid subid, TransactionId xid)
+{
+	snprintf(path, MAXPGPATH, "%u-%u.changes", subid, xid);
+}
+
+/*
+ * stream_cleanup_files
+ *	  Cleanup files for a subscription / toplevel transaction.
+ *
+ * Remove files with serialized changes and subxact info for a particular
+ * toplevel transaction. Each subscription has a separate set of files.
+ */
+static void
+stream_cleanup_files(Oid subid, TransactionId xid)
+{
+	char		path[MAXPGPATH];
+	StreamXidHash *ent;
+
+	/* Find the xid entry in the xidhash */
+	ent = (StreamXidHash *) hash_search(xidhash,
+										(void *) &xid,
+										HASH_FIND,
+										NULL);
+	if (!ent)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("transaction %u not found in stream XID hash table",
+								 xid)));
+
+	/* Delete the change file and release the stream fileset memory */
+	changes_filename(path, subid, xid);
+	SharedFileSetDeleteAll(ent->stream_fileset);
+	pfree(ent->stream_fileset);
+	ent->stream_fileset = NULL;
+
+	/* Delete the subxact file and release the memory, if it exist */
+	if (ent->subxact_fileset)
+	{
+		subxact_filename(path, subid, xid);
+		SharedFileSetDeleteAll(ent->subxact_fileset);
+		pfree(ent->subxact_fileset);
+		ent->subxact_fileset = NULL;
+	}
+
+	/* Remove the xid entry from the stream xid hash */
+	hash_search(xidhash, (void *) &xid, HASH_REMOVE, NULL);
+}
+
+/*
+ * stream_open_file
+ *	  Open a file that we'll use to serialize changes for a toplevel
+ * transaction.
+ *
+ * Open a file for streamed changes from a toplevel transaction identified
+ * by stream_xid (global variable). If it's the first chunk of streamed
+ * changes for this transaction, initialize the shared fileset and create the
+ * buffile, otherwise open the previously created file.
+ *
+ * This can only be called at the beginning of a "streaming" block, i.e.
+ * between stream_start/stream_stop messages from the upstream.
+ */
+static void
+stream_open_file(Oid subid, TransactionId xid, bool first_segment)
+{
+	char		path[MAXPGPATH];
+	bool		found;
+	MemoryContext oldcxt;
+	StreamXidHash *ent;
+
+	Assert(in_streamed_transaction);
+	Assert(OidIsValid(subid));
+	Assert(TransactionIdIsValid(xid));
+	Assert(stream_fd == NULL);
+
+	/* create or find the xid entry in the xidhash */
+	ent = (StreamXidHash *) hash_search(xidhash,
+										(void *) &xid,
+										HASH_ENTER,
+										&found);
+
+	changes_filename(path, subid, xid);
+	elog(DEBUG1, "opening file \"%s\" for streamed changes", path);
+
+	/*
+	 * Create/open the buffiles under the logical streaming context so that we
+	 * have those files until stream stop.
+	 */
+	oldcxt = MemoryContextSwitchTo(LogicalStreamingContext);
+
+	/*
+	 * If this is the first streamed segment, the file must not exist, so make
+	 * sure we're the ones creating it. Otherwise just open the file for
+	 * writing, in append mode.
+	 */
+	if (first_segment)
+	{
+		MemoryContext savectx;
+		SharedFileSet *fileset;
+
+		if (found)
+			ereport(ERROR,
+					(errcode(ERRCODE_PROTOCOL_VIOLATION),
+					 errmsg_internal("incorrect first-segment flag for streamed replication transaction")));
+
+		/*
+		 * We need to maintain shared fileset across multiple stream
+		 * start/stop calls. So, need to allocate it in a persistent context.
+		 */
+		savectx = MemoryContextSwitchTo(ApplyContext);
+		fileset = palloc(sizeof(SharedFileSet));
+
+		SharedFileSetInit(fileset, NULL);
+		MemoryContextSwitchTo(savectx);
+
+		stream_fd = BufFileCreateShared(fileset, path);
+
+		/* Remember the fileset for the next stream of the same transaction */
+		ent->xid = xid;
+		ent->stream_fileset = fileset;
+		ent->subxact_fileset = NULL;
+	}
+	else
+	{
+		if (!found)
+			ereport(ERROR,
+					(errcode(ERRCODE_PROTOCOL_VIOLATION),
+					 errmsg_internal("incorrect first-segment flag for streamed replication transaction")));
+
+		/*
+		 * Open the file and seek to the end of the file because we always
+		 * append the changes file.
+		 */
+		stream_fd = BufFileOpenShared(ent->stream_fileset, path, O_RDWR);
+		BufFileSeek(stream_fd, 0, 0, SEEK_END);
+	}
+
+	MemoryContextSwitchTo(oldcxt);
+}
+
+/*
+ * stream_close_file
+ *	  Close the currently open file with streamed changes.
+ *
+ * This can only be called at the end of a streaming block, i.e. at stream_stop
+ * message from the upstream.
+ */
+static void
+stream_close_file(void)
+{
+	Assert(in_streamed_transaction);
+	Assert(TransactionIdIsValid(stream_xid));
+	Assert(stream_fd != NULL);
+
+	BufFileClose(stream_fd);
+
+	stream_xid = InvalidTransactionId;
+	stream_fd = NULL;
+}
+
+/*
+ * stream_write_change
+ *	  Serialize a change to a file for the current toplevel transaction.
+ *
+ * The change is serialized in a simple format, with length (not including
+ * the length), action code (identifying the message type) and message
+ * contents (without the subxact TransactionId value).
+ */
+static void
+stream_write_change(char action, StringInfo s)
+{
+	int			len;
+
+	Assert(in_streamed_transaction);
+	Assert(TransactionIdIsValid(stream_xid));
+	Assert(stream_fd != NULL);
+
+	/* total on-disk size, including the action type character */
+	len = (s->len - s->cursor) + sizeof(char);
+
+	/* first write the size */
+	BufFileWrite(stream_fd, &len, sizeof(len));
+
+	/* then the action */
+	BufFileWrite(stream_fd, &action, sizeof(action));
+
+	/* and finally the remaining part of the buffer (after the XID) */
+	len = (s->len - s->cursor);
+
+	BufFileWrite(stream_fd, &s->data[s->cursor], len);
+}
+
+/*
+ * Cleanup the memory for subxacts and reset the related variables.
+ */
+static inline void
+cleanup_subxact_info()
+{
+	if (subxact_data.subxacts)
+		pfree(subxact_data.subxacts);
+
+	subxact_data.subxacts = NULL;
+	subxact_data.subxact_last = InvalidTransactionId;
+	subxact_data.nsubxacts = 0;
+	subxact_data.nsubxacts_max = 0;
+}
+
+/* Logical Replication Apply worker entry point */
+void
+ApplyWorkerMain(Datum main_arg)
+{
+	int			worker_slot = DatumGetInt32(main_arg);
+	MemoryContext oldctx;
+	char		originname[NAMEDATALEN];
+	XLogRecPtr	origin_startpos;
+	char	   *myslotname;
+	WalRcvStreamOptions options;
+
+	/* Attach to slot */
+	logicalrep_worker_attach(worker_slot);
+
+	/* Setup signal handling */
+	pqsignal(SIGHUP, SignalHandlerForConfigReload);
+	pqsignal(SIGTERM, die);
+	BackgroundWorkerUnblockSignals();
+
+	/*
+	 * We don't currently need any ResourceOwner in a walreceiver process, but
+	 * if we did, we could call CreateAuxProcessResourceOwner here.
+	 */
+
+	/* Initialise stats to a sanish value */
+	MyLogicalRepWorker->last_send_time = MyLogicalRepWorker->last_recv_time =
+		MyLogicalRepWorker->reply_time = GetCurrentTimestamp();
+
+	/* Load the libpq-specific functions */
+	load_file("libpqwalreceiver", false);
+
+	/* Run as replica session replication role. */
+	SetConfigOption("session_replication_role", "replica",
+					PGC_SUSET, PGC_S_OVERRIDE);
+
+	/* Connect to our database. */
+	BackgroundWorkerInitializeConnectionByOid(MyLogicalRepWorker->dbid,
+											  MyLogicalRepWorker->userid,
+											  0);
+
+	/*
+	 * Set always-secure search path, so malicious users can't redirect user
+	 * code (e.g. pg_index.indexprs).
+	 */
+	SetConfigOption("search_path", "", PGC_SUSET, PGC_S_OVERRIDE);
+
+	/* Load the subscription into persistent memory context. */
+	ApplyContext = AllocSetContextCreate(TopMemoryContext,
+										 "ApplyContext",
+										 ALLOCSET_DEFAULT_SIZES);
+	StartTransactionCommand();
+	oldctx = MemoryContextSwitchTo(ApplyContext);
+
+	MySubscription = GetSubscription(MyLogicalRepWorker->subid, true);
+	if (!MySubscription)
+	{
+		ereport(LOG,
+				(errmsg("logical replication apply worker for subscription %u will not "
+						"start because the subscription was removed during startup",
+						MyLogicalRepWorker->subid)));
+		proc_exit(0);
+	}
+
+	MySubscriptionValid = true;
+	MemoryContextSwitchTo(oldctx);
+
+	if (!MySubscription->enabled)
+	{
+		ereport(LOG,
+				(errmsg("logical replication apply worker for subscription \"%s\" will not "
+						"start because the subscription was disabled during startup",
+						MySubscription->name)));
+
+		proc_exit(0);
+	}
+
+	/* Setup synchronous commit according to the user's wishes */
+	SetConfigOption("synchronous_commit", MySubscription->synccommit,
+					PGC_BACKEND, PGC_S_OVERRIDE);
+
+	/* Keep us informed about subscription changes. */
+	CacheRegisterSyscacheCallback(SUBSCRIPTIONOID,
+								  subscription_change_cb,
+								  (Datum) 0);
+
+	if (am_tablesync_worker())
+		ereport(LOG,
+				(errmsg("logical replication table synchronization worker for subscription \"%s\", table \"%s\" has started",
+						MySubscription->name, get_rel_name(MyLogicalRepWorker->relid))));
+	else
+		ereport(LOG,
+				(errmsg("logical replication apply worker for subscription \"%s\" has started",
+						MySubscription->name)));
+
+	CommitTransactionCommand();
+
+	/* Connect to the origin and start the replication. */
+	elog(DEBUG1, "connecting to publisher using connection string \"%s\"",
+		 MySubscription->conninfo);
+
+	if (am_tablesync_worker())
+	{
+		char	   *syncslotname;
+
+		/* This is table synchronization worker, call initial sync. */
+		syncslotname = LogicalRepSyncTableStart(&origin_startpos);
+
+		/* allocate slot name in long-lived context */
+		myslotname = MemoryContextStrdup(ApplyContext, syncslotname);
+
+		pfree(syncslotname);
+	}
+	else
+	{
+		/* This is main apply worker */
+		RepOriginId originid;
+		TimeLineID	startpointTLI;
+		char	   *err;
+
+		myslotname = MySubscription->slotname;
+
+		/*
+		 * This shouldn't happen if the subscription is enabled, but guard
+		 * against DDL bugs or manual catalog changes.  (libpqwalreceiver will
+		 * crash if slot is NULL.)
+		 */
+		if (!myslotname)
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("subscription has no replication slot set")));
+
+		/* Setup replication origin tracking. */
+		StartTransactionCommand();
+		snprintf(originname, sizeof(originname), "pg_%u", MySubscription->oid);
+		originid = replorigin_by_name(originname, true);
+		if (!OidIsValid(originid))
+			originid = replorigin_create(originname);
+		replorigin_session_setup(originid);
+		replorigin_session_origin = originid;
+		origin_startpos = replorigin_session_get_progress(false);
+		CommitTransactionCommand();
+
+		LogRepWorkerWalRcvConn = walrcv_connect(MySubscription->conninfo, true,
+												MySubscription->name, &err);
+		if (LogRepWorkerWalRcvConn == NULL)
+			ereport(ERROR,
+					(errcode(ERRCODE_CONNECTION_FAILURE),
+					 errmsg("could not connect to the publisher: %s", err)));
+
+		/*
+		 * We don't really use the output identify_system for anything but it
+		 * does some initializations on the upstream so let's still call it.
+		 */
+		(void) walrcv_identify_system(LogRepWorkerWalRcvConn, &startpointTLI);
+	}
+
+	/*
+	 * Setup callback for syscache so that we know when something changes in
+	 * the subscription relation state.
+	 */
+	CacheRegisterSyscacheCallback(SUBSCRIPTIONRELMAP,
+								  invalidate_syncing_table_states,
+								  (Datum) 0);
+
+	/* Build logical replication streaming options. */
+	options.logical = true;
+	options.startpoint = origin_startpos;
+	options.slotname = myslotname;
+	options.proto.logical.proto_version =
+		walrcv_server_version(LogRepWorkerWalRcvConn) >= 140000 ?
+		LOGICALREP_PROTO_STREAM_VERSION_NUM : LOGICALREP_PROTO_VERSION_NUM;
+	options.proto.logical.publication_names = MySubscription->publications;
+	options.proto.logical.binary = MySubscription->binary;
+	options.proto.logical.streaming = MySubscription->stream;
+
+	/* Start normal logical streaming replication. */
+	walrcv_startstreaming(LogRepWorkerWalRcvConn, &options);
+
+	/* Run the main loop. */
+	LogicalRepApplyLoop(origin_startpos);
+
+	proc_exit(0);
+}
+
+/*
+ * Is current process a logical replication worker?
+ */
+bool
+IsLogicalWorker(void)
+{
+	return MyLogicalRepWorker != NULL;
+}