Adding upstream version 14.5.upstream/14.5upstream

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

1 files changed, 1024 insertions, 0 deletions

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;
+}