Adding upstream version 14.5.upstream/14.5upstream

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

1 files changed, 1409 insertions, 0 deletions

diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
new file mode 100644
index 0000000..b4bca7e
--- /dev/null
+++ b/src/backend/storage/smgr/md.c
@@ -0,0 +1,1409 @@
+/*-------------------------------------------------------------------------
+ *
+ * md.c
+ *	  This code manages relations that reside on magnetic disk.
+ *
+ * Or at least, that was what the Berkeley folk had in mind when they named
+ * this file.  In reality, what this code provides is an interface from
+ * the smgr API to Unix-like filesystem APIs, so it will work with any type
+ * of device for which the operating system provides filesystem support.
+ * It doesn't matter whether the bits are on spinning rust or some other
+ * storage technology.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/storage/smgr/md.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/file.h>
+
+#include "access/xlog.h"
+#include "access/xlogutils.h"
+#include "commands/tablespace.h"
+#include "miscadmin.h"
+#include "pg_trace.h"
+#include "pgstat.h"
+#include "postmaster/bgwriter.h"
+#include "storage/bufmgr.h"
+#include "storage/fd.h"
+#include "storage/md.h"
+#include "storage/relfilenode.h"
+#include "storage/smgr.h"
+#include "storage/sync.h"
+#include "utils/hsearch.h"
+#include "utils/memutils.h"
+
+/*
+ *	The magnetic disk storage manager keeps track of open file
+ *	descriptors in its own descriptor pool.  This is done to make it
+ *	easier to support relations that are larger than the operating
+ *	system's file size limit (often 2GBytes).  In order to do that,
+ *	we break relations up into "segment" files that are each shorter than
+ *	the OS file size limit.  The segment size is set by the RELSEG_SIZE
+ *	configuration constant in pg_config.h.
+ *
+ *	On disk, a relation must consist of consecutively numbered segment
+ *	files in the pattern
+ *		-- Zero or more full segments of exactly RELSEG_SIZE blocks each
+ *		-- Exactly one partial segment of size 0 <= size < RELSEG_SIZE blocks
+ *		-- Optionally, any number of inactive segments of size 0 blocks.
+ *	The full and partial segments are collectively the "active" segments.
+ *	Inactive segments are those that once contained data but are currently
+ *	not needed because of an mdtruncate() operation.  The reason for leaving
+ *	them present at size zero, rather than unlinking them, is that other
+ *	backends and/or the checkpointer might be holding open file references to
+ *	such segments.  If the relation expands again after mdtruncate(), such
+ *	that a deactivated segment becomes active again, it is important that
+ *	such file references still be valid --- else data might get written
+ *	out to an unlinked old copy of a segment file that will eventually
+ *	disappear.
+ *
+ *	File descriptors are stored in the per-fork md_seg_fds arrays inside
+ *	SMgrRelation. The length of these arrays is stored in md_num_open_segs.
+ *	Note that a fork's md_num_open_segs having a specific value does not
+ *	necessarily mean the relation doesn't have additional segments; we may
+ *	just not have opened the next segment yet.  (We could not have "all
+ *	segments are in the array" as an invariant anyway, since another backend
+ *	could extend the relation while we aren't looking.)  We do not have
+ *	entries for inactive segments, however; as soon as we find a partial
+ *	segment, we assume that any subsequent segments are inactive.
+ *
+ *	The entire MdfdVec array is palloc'd in the MdCxt memory context.
+ */
+
+typedef struct _MdfdVec
+{
+	File		mdfd_vfd;		/* fd number in fd.c's pool */
+	BlockNumber mdfd_segno;		/* segment number, from 0 */
+} MdfdVec;
+
+static MemoryContext MdCxt;		/* context for all MdfdVec objects */
+
+
+/* Populate a file tag describing an md.c segment file. */
+#define INIT_MD_FILETAG(a,xx_rnode,xx_forknum,xx_segno) \
+( \
+	memset(&(a), 0, sizeof(FileTag)), \
+	(a).handler = SYNC_HANDLER_MD, \
+	(a).rnode = (xx_rnode), \
+	(a).forknum = (xx_forknum), \
+	(a).segno = (xx_segno) \
+)
+
+
+/*** behavior for mdopen & _mdfd_getseg ***/
+/* ereport if segment not present */
+#define EXTENSION_FAIL				(1 << 0)
+/* return NULL if segment not present */
+#define EXTENSION_RETURN_NULL		(1 << 1)
+/* create new segments as needed */
+#define EXTENSION_CREATE			(1 << 2)
+/* create new segments if needed during recovery */
+#define EXTENSION_CREATE_RECOVERY	(1 << 3)
+/*
+ * Allow opening segments which are preceded by segments smaller than
+ * RELSEG_SIZE, e.g. inactive segments (see above). Note that this breaks
+ * mdnblocks() and related functionality henceforth - which currently is ok,
+ * because this is only required in the checkpointer which never uses
+ * mdnblocks().
+ */
+#define EXTENSION_DONT_CHECK_SIZE	(1 << 4)
+
+
+/* local routines */
+static void mdunlinkfork(RelFileNodeBackend rnode, ForkNumber forkNum,
+						 bool isRedo);
+static MdfdVec *mdopenfork(SMgrRelation reln, ForkNumber forknum, int behavior);
+static void register_dirty_segment(SMgrRelation reln, ForkNumber forknum,
+								   MdfdVec *seg);
+static void register_unlink_segment(RelFileNodeBackend rnode, ForkNumber forknum,
+									BlockNumber segno);
+static void register_forget_request(RelFileNodeBackend rnode, ForkNumber forknum,
+									BlockNumber segno);
+static void _fdvec_resize(SMgrRelation reln,
+						  ForkNumber forknum,
+						  int nseg);
+static char *_mdfd_segpath(SMgrRelation reln, ForkNumber forknum,
+						   BlockNumber segno);
+static MdfdVec *_mdfd_openseg(SMgrRelation reln, ForkNumber forkno,
+							  BlockNumber segno, int oflags);
+static MdfdVec *_mdfd_getseg(SMgrRelation reln, ForkNumber forkno,
+							 BlockNumber blkno, bool skipFsync, int behavior);
+static BlockNumber _mdnblocks(SMgrRelation reln, ForkNumber forknum,
+							  MdfdVec *seg);
+
+
+/*
+ *	mdinit() -- Initialize private state for magnetic disk storage manager.
+ */
+void
+mdinit(void)
+{
+	MdCxt = AllocSetContextCreate(TopMemoryContext,
+								  "MdSmgr",
+								  ALLOCSET_DEFAULT_SIZES);
+}
+
+/*
+ *	mdexists() -- Does the physical file exist?
+ *
+ * Note: this will return true for lingering files, with pending deletions
+ */
+bool
+mdexists(SMgrRelation reln, ForkNumber forkNum)
+{
+	/*
+	 * Close it first, to ensure that we notice if the fork has been unlinked
+	 * since we opened it.
+	 */
+	mdclose(reln, forkNum);
+
+	return (mdopenfork(reln, forkNum, EXTENSION_RETURN_NULL) != NULL);
+}
+
+/*
+ *	mdcreate() -- Create a new relation on magnetic disk.
+ *
+ * If isRedo is true, it's okay for the relation to exist already.
+ */
+void
+mdcreate(SMgrRelation reln, ForkNumber forkNum, bool isRedo)
+{
+	MdfdVec    *mdfd;
+	char	   *path;
+	File		fd;
+
+	if (isRedo && reln->md_num_open_segs[forkNum] > 0)
+		return;					/* created and opened already... */
+
+	Assert(reln->md_num_open_segs[forkNum] == 0);
+
+	/*
+	 * We may be using the target table space for the first time in this
+	 * database, so create a per-database subdirectory if needed.
+	 *
+	 * XXX this is a fairly ugly violation of module layering, but this seems
+	 * to be the best place to put the check.  Maybe TablespaceCreateDbspace
+	 * should be here and not in commands/tablespace.c?  But that would imply
+	 * importing a lot of stuff that smgr.c oughtn't know, either.
+	 */
+	TablespaceCreateDbspace(reln->smgr_rnode.node.spcNode,
+							reln->smgr_rnode.node.dbNode,
+							isRedo);
+
+	path = relpath(reln->smgr_rnode, forkNum);
+
+	fd = PathNameOpenFile(path, O_RDWR | O_CREAT | O_EXCL | PG_BINARY);
+
+	if (fd < 0)
+	{
+		int			save_errno = errno;
+
+		if (isRedo)
+			fd = PathNameOpenFile(path, O_RDWR | PG_BINARY);
+		if (fd < 0)
+		{
+			/* be sure to report the error reported by create, not open */
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not create file \"%s\": %m", path)));
+		}
+	}
+
+	pfree(path);
+
+	_fdvec_resize(reln, forkNum, 1);
+	mdfd = &reln->md_seg_fds[forkNum][0];
+	mdfd->mdfd_vfd = fd;
+	mdfd->mdfd_segno = 0;
+}
+
+/*
+ *	mdunlink() -- Unlink a relation.
+ *
+ * Note that we're passed a RelFileNodeBackend --- by the time this is called,
+ * there won't be an SMgrRelation hashtable entry anymore.
+ *
+ * forkNum can be a fork number to delete a specific fork, or InvalidForkNumber
+ * to delete all forks.
+ *
+ * For regular relations, we don't unlink the first segment file of the rel,
+ * but just truncate it to zero length, and record a request to unlink it after
+ * the next checkpoint.  Additional segments can be unlinked immediately,
+ * however.  Leaving the empty file in place prevents that relfilenode
+ * number from being reused.  The scenario this protects us from is:
+ * 1. We delete a relation (and commit, and actually remove its file).
+ * 2. We create a new relation, which by chance gets the same relfilenode as
+ *	  the just-deleted one (OIDs must've wrapped around for that to happen).
+ * 3. We crash before another checkpoint occurs.
+ * During replay, we would delete the file and then recreate it, which is fine
+ * if the contents of the file were repopulated by subsequent WAL entries.
+ * But if we didn't WAL-log insertions, but instead relied on fsyncing the
+ * file after populating it (as we do at wal_level=minimal), the contents of
+ * the file would be lost forever.  By leaving the empty file until after the
+ * next checkpoint, we prevent reassignment of the relfilenode number until
+ * it's safe, because relfilenode assignment skips over any existing file.
+ *
+ * We do not need to go through this dance for temp relations, though, because
+ * we never make WAL entries for temp rels, and so a temp rel poses no threat
+ * to the health of a regular rel that has taken over its relfilenode number.
+ * The fact that temp rels and regular rels have different file naming
+ * patterns provides additional safety.
+ *
+ * All the above applies only to the relation's main fork; other forks can
+ * just be removed immediately, since they are not needed to prevent the
+ * relfilenode number from being recycled.  Also, we do not carefully
+ * track whether other forks have been created or not, but just attempt to
+ * unlink them unconditionally; so we should never complain about ENOENT.
+ *
+ * If isRedo is true, it's unsurprising for the relation to be already gone.
+ * Also, we should remove the file immediately instead of queuing a request
+ * for later, since during redo there's no possibility of creating a
+ * conflicting relation.
+ *
+ * Note: any failure should be reported as WARNING not ERROR, because
+ * we are usually not in a transaction anymore when this is called.
+ */
+void
+mdunlink(RelFileNodeBackend rnode, ForkNumber forkNum, bool isRedo)
+{
+	/* Now do the per-fork work */
+	if (forkNum == InvalidForkNumber)
+	{
+		for (forkNum = 0; forkNum <= MAX_FORKNUM; forkNum++)
+			mdunlinkfork(rnode, forkNum, isRedo);
+	}
+	else
+		mdunlinkfork(rnode, forkNum, isRedo);
+}
+
+/*
+ * Truncate a file to release disk space.
+ */
+static int
+do_truncate(const char *path)
+{
+	int			save_errno;
+	int			ret;
+
+	ret = pg_truncate(path, 0);
+
+	/* Log a warning here to avoid repetition in callers. */
+	if (ret < 0 && errno != ENOENT)
+	{
+		save_errno = errno;
+		ereport(WARNING,
+				(errcode_for_file_access(),
+				 errmsg("could not truncate file \"%s\": %m", path)));
+		errno = save_errno;
+	}
+
+	return ret;
+}
+
+static void
+mdunlinkfork(RelFileNodeBackend rnode, ForkNumber forkNum, bool isRedo)
+{
+	char	   *path;
+	int			ret;
+
+	path = relpath(rnode, forkNum);
+
+	/*
+	 * Delete or truncate the first segment.
+	 */
+	if (isRedo || forkNum != MAIN_FORKNUM || RelFileNodeBackendIsTemp(rnode))
+	{
+		if (!RelFileNodeBackendIsTemp(rnode))
+		{
+			/* Prevent other backends' fds from holding on to the disk space */
+			ret = do_truncate(path);
+
+			/* Forget any pending sync requests for the first segment */
+			register_forget_request(rnode, forkNum, 0 /* first seg */ );
+		}
+		else
+			ret = 0;
+
+		/* Next unlink the file, unless it was already found to be missing */
+		if (ret == 0 || errno != ENOENT)
+		{
+			ret = unlink(path);
+			if (ret < 0 && errno != ENOENT)
+				ereport(WARNING,
+						(errcode_for_file_access(),
+						 errmsg("could not remove file \"%s\": %m", path)));
+		}
+	}
+	else
+	{
+		/* Prevent other backends' fds from holding on to the disk space */
+		ret = do_truncate(path);
+
+		/* Register request to unlink first segment later */
+		register_unlink_segment(rnode, forkNum, 0 /* first seg */ );
+	}
+
+	/*
+	 * Delete any additional segments.
+	 */
+	if (ret >= 0)
+	{
+		char	   *segpath = (char *) palloc(strlen(path) + 12);
+		BlockNumber segno;
+
+		/*
+		 * Note that because we loop until getting ENOENT, we will correctly
+		 * remove all inactive segments as well as active ones.
+		 */
+		for (segno = 1;; segno++)
+		{
+			sprintf(segpath, "%s.%u", path, segno);
+
+			if (!RelFileNodeBackendIsTemp(rnode))
+			{
+				/*
+				 * Prevent other backends' fds from holding on to the disk
+				 * space.
+				 */
+				if (do_truncate(segpath) < 0 && errno == ENOENT)
+					break;
+
+				/*
+				 * Forget any pending sync requests for this segment before we
+				 * try to unlink.
+				 */
+				register_forget_request(rnode, forkNum, segno);
+			}
+
+			if (unlink(segpath) < 0)
+			{
+				/* ENOENT is expected after the last segment... */
+				if (errno != ENOENT)
+					ereport(WARNING,
+							(errcode_for_file_access(),
+							 errmsg("could not remove file \"%s\": %m", segpath)));
+				break;
+			}
+		}
+		pfree(segpath);
+	}
+
+	pfree(path);
+}
+
+/*
+ *	mdextend() -- Add a block to the specified relation.
+ *
+ *		The semantics are nearly the same as mdwrite(): write at the
+ *		specified position.  However, this is to be used for the case of
+ *		extending a relation (i.e., blocknum is at or beyond the current
+ *		EOF).  Note that we assume writing a block beyond current EOF
+ *		causes intervening file space to become filled with zeroes.
+ */
+void
+mdextend(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
+		 char *buffer, bool skipFsync)
+{
+	off_t		seekpos;
+	int			nbytes;
+	MdfdVec    *v;
+
+	/* This assert is too expensive to have on normally ... */
+#ifdef CHECK_WRITE_VS_EXTEND
+	Assert(blocknum >= mdnblocks(reln, forknum));
+#endif
+
+	/*
+	 * If a relation manages to grow to 2^32-1 blocks, refuse to extend it any
+	 * more --- we mustn't create a block whose number actually is
+	 * InvalidBlockNumber.  (Note that this failure should be unreachable
+	 * because of upstream checks in bufmgr.c.)
+	 */
+	if (blocknum == InvalidBlockNumber)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+				 errmsg("cannot extend file \"%s\" beyond %u blocks",
+						relpath(reln->smgr_rnode, forknum),
+						InvalidBlockNumber)));
+
+	v = _mdfd_getseg(reln, forknum, blocknum, skipFsync, EXTENSION_CREATE);
+
+	seekpos = (off_t) BLCKSZ * (blocknum % ((BlockNumber) RELSEG_SIZE));
+
+	Assert(seekpos < (off_t) BLCKSZ * RELSEG_SIZE);
+
+	if ((nbytes = FileWrite(v->mdfd_vfd, buffer, BLCKSZ, seekpos, WAIT_EVENT_DATA_FILE_EXTEND)) != BLCKSZ)
+	{
+		if (nbytes < 0)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not extend file \"%s\": %m",
+							FilePathName(v->mdfd_vfd)),
+					 errhint("Check free disk space.")));
+		/* short write: complain appropriately */
+		ereport(ERROR,
+				(errcode(ERRCODE_DISK_FULL),
+				 errmsg("could not extend file \"%s\": wrote only %d of %d bytes at block %u",
+						FilePathName(v->mdfd_vfd),
+						nbytes, BLCKSZ, blocknum),
+				 errhint("Check free disk space.")));
+	}
+
+	if (!skipFsync && !SmgrIsTemp(reln))
+		register_dirty_segment(reln, forknum, v);
+
+	Assert(_mdnblocks(reln, forknum, v) <= ((BlockNumber) RELSEG_SIZE));
+}
+
+/*
+ *	mdopenfork() -- Open one fork of the specified relation.
+ *
+ * Note we only open the first segment, when there are multiple segments.
+ *
+ * If first segment is not present, either ereport or return NULL according
+ * to "behavior".  We treat EXTENSION_CREATE the same as EXTENSION_FAIL;
+ * EXTENSION_CREATE means it's OK to extend an existing relation, not to
+ * invent one out of whole cloth.
+ */
+static MdfdVec *
+mdopenfork(SMgrRelation reln, ForkNumber forknum, int behavior)
+{
+	MdfdVec    *mdfd;
+	char	   *path;
+	File		fd;
+
+	/* No work if already open */
+	if (reln->md_num_open_segs[forknum] > 0)
+		return &reln->md_seg_fds[forknum][0];
+
+	path = relpath(reln->smgr_rnode, forknum);
+
+	fd = PathNameOpenFile(path, O_RDWR | PG_BINARY);
+
+	if (fd < 0)
+	{
+		if ((behavior & EXTENSION_RETURN_NULL) &&
+			FILE_POSSIBLY_DELETED(errno))
+		{
+			pfree(path);
+			return NULL;
+		}
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not open file \"%s\": %m", path)));
+	}
+
+	pfree(path);
+
+	_fdvec_resize(reln, forknum, 1);
+	mdfd = &reln->md_seg_fds[forknum][0];
+	mdfd->mdfd_vfd = fd;
+	mdfd->mdfd_segno = 0;
+
+	Assert(_mdnblocks(reln, forknum, mdfd) <= ((BlockNumber) RELSEG_SIZE));
+
+	return mdfd;
+}
+
+/*
+ *  mdopen() -- Initialize newly-opened relation.
+ */
+void
+mdopen(SMgrRelation reln)
+{
+	/* mark it not open */
+	for (int forknum = 0; forknum <= MAX_FORKNUM; forknum++)
+		reln->md_num_open_segs[forknum] = 0;
+}
+
+/*
+ *	mdclose() -- Close the specified relation, if it isn't closed already.
+ */
+void
+mdclose(SMgrRelation reln, ForkNumber forknum)
+{
+	int			nopensegs = reln->md_num_open_segs[forknum];
+
+	/* No work if already closed */
+	if (nopensegs == 0)
+		return;
+
+	/* close segments starting from the end */
+	while (nopensegs > 0)
+	{
+		MdfdVec    *v = &reln->md_seg_fds[forknum][nopensegs - 1];
+
+		FileClose(v->mdfd_vfd);
+		_fdvec_resize(reln, forknum, nopensegs - 1);
+		nopensegs--;
+	}
+}
+
+/*
+ *	mdprefetch() -- Initiate asynchronous read of the specified block of a relation
+ */
+bool
+mdprefetch(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum)
+{
+#ifdef USE_PREFETCH
+	off_t		seekpos;
+	MdfdVec    *v;
+
+	v = _mdfd_getseg(reln, forknum, blocknum, false,
+					 InRecovery ? EXTENSION_RETURN_NULL : EXTENSION_FAIL);
+	if (v == NULL)
+		return false;
+
+	seekpos = (off_t) BLCKSZ * (blocknum % ((BlockNumber) RELSEG_SIZE));
+
+	Assert(seekpos < (off_t) BLCKSZ * RELSEG_SIZE);
+
+	(void) FilePrefetch(v->mdfd_vfd, seekpos, BLCKSZ, WAIT_EVENT_DATA_FILE_PREFETCH);
+#endif							/* USE_PREFETCH */
+
+	return true;
+}
+
+/*
+ * mdwriteback() -- Tell the kernel to write pages back to storage.
+ *
+ * This accepts a range of blocks because flushing several pages at once is
+ * considerably more efficient than doing so individually.
+ */
+void
+mdwriteback(SMgrRelation reln, ForkNumber forknum,
+			BlockNumber blocknum, BlockNumber nblocks)
+{
+	/*
+	 * Issue flush requests in as few requests as possible; have to split at
+	 * segment boundaries though, since those are actually separate files.
+	 */
+	while (nblocks > 0)
+	{
+		BlockNumber nflush = nblocks;
+		off_t		seekpos;
+		MdfdVec    *v;
+		int			segnum_start,
+					segnum_end;
+
+		v = _mdfd_getseg(reln, forknum, blocknum, true /* not used */ ,
+						 EXTENSION_RETURN_NULL);
+
+		/*
+		 * We might be flushing buffers of already removed relations, that's
+		 * ok, just ignore that case.
+		 */
+		if (!v)
+			return;
+
+		/* compute offset inside the current segment */
+		segnum_start = blocknum / RELSEG_SIZE;
+
+		/* compute number of desired writes within the current segment */
+		segnum_end = (blocknum + nblocks - 1) / RELSEG_SIZE;
+		if (segnum_start != segnum_end)
+			nflush = RELSEG_SIZE - (blocknum % ((BlockNumber) RELSEG_SIZE));
+
+		Assert(nflush >= 1);
+		Assert(nflush <= nblocks);
+
+		seekpos = (off_t) BLCKSZ * (blocknum % ((BlockNumber) RELSEG_SIZE));
+
+		FileWriteback(v->mdfd_vfd, seekpos, (off_t) BLCKSZ * nflush, WAIT_EVENT_DATA_FILE_FLUSH);
+
+		nblocks -= nflush;
+		blocknum += nflush;
+	}
+}
+
+/*
+ *	mdread() -- Read the specified block from a relation.
+ */
+void
+mdread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
+	   char *buffer)
+{
+	off_t		seekpos;
+	int			nbytes;
+	MdfdVec    *v;
+
+	TRACE_POSTGRESQL_SMGR_MD_READ_START(forknum, blocknum,
+										reln->smgr_rnode.node.spcNode,
+										reln->smgr_rnode.node.dbNode,
+										reln->smgr_rnode.node.relNode,
+										reln->smgr_rnode.backend);
+
+	v = _mdfd_getseg(reln, forknum, blocknum, false,
+					 EXTENSION_FAIL | EXTENSION_CREATE_RECOVERY);
+
+	seekpos = (off_t) BLCKSZ * (blocknum % ((BlockNumber) RELSEG_SIZE));
+
+	Assert(seekpos < (off_t) BLCKSZ * RELSEG_SIZE);
+
+	nbytes = FileRead(v->mdfd_vfd, buffer, BLCKSZ, seekpos, WAIT_EVENT_DATA_FILE_READ);
+
+	TRACE_POSTGRESQL_SMGR_MD_READ_DONE(forknum, blocknum,
+									   reln->smgr_rnode.node.spcNode,
+									   reln->smgr_rnode.node.dbNode,
+									   reln->smgr_rnode.node.relNode,
+									   reln->smgr_rnode.backend,
+									   nbytes,
+									   BLCKSZ);
+
+	if (nbytes != BLCKSZ)
+	{
+		if (nbytes < 0)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read block %u in file \"%s\": %m",
+							blocknum, FilePathName(v->mdfd_vfd))));
+
+		/*
+		 * Short read: we are at or past EOF, or we read a partial block at
+		 * EOF.  Normally this is an error; upper levels should never try to
+		 * read a nonexistent block.  However, if zero_damaged_pages is ON or
+		 * we are InRecovery, we should instead return zeroes without
+		 * complaining.  This allows, for example, the case of trying to
+		 * update a block that was later truncated away.
+		 */
+		if (zero_damaged_pages || InRecovery)
+			MemSet(buffer, 0, BLCKSZ);
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_DATA_CORRUPTED),
+					 errmsg("could not read block %u in file \"%s\": read only %d of %d bytes",
+							blocknum, FilePathName(v->mdfd_vfd),
+							nbytes, BLCKSZ)));
+	}
+}
+
+/*
+ *	mdwrite() -- Write the supplied block at the appropriate location.
+ *
+ *		This is to be used only for updating already-existing blocks of a
+ *		relation (ie, those before the current EOF).  To extend a relation,
+ *		use mdextend().
+ */
+void
+mdwrite(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
+		char *buffer, bool skipFsync)
+{
+	off_t		seekpos;
+	int			nbytes;
+	MdfdVec    *v;
+
+	/* This assert is too expensive to have on normally ... */
+#ifdef CHECK_WRITE_VS_EXTEND
+	Assert(blocknum < mdnblocks(reln, forknum));
+#endif
+
+	TRACE_POSTGRESQL_SMGR_MD_WRITE_START(forknum, blocknum,
+										 reln->smgr_rnode.node.spcNode,
+										 reln->smgr_rnode.node.dbNode,
+										 reln->smgr_rnode.node.relNode,
+										 reln->smgr_rnode.backend);
+
+	v = _mdfd_getseg(reln, forknum, blocknum, skipFsync,
+					 EXTENSION_FAIL | EXTENSION_CREATE_RECOVERY);
+
+	seekpos = (off_t) BLCKSZ * (blocknum % ((BlockNumber) RELSEG_SIZE));
+
+	Assert(seekpos < (off_t) BLCKSZ * RELSEG_SIZE);
+
+	nbytes = FileWrite(v->mdfd_vfd, buffer, BLCKSZ, seekpos, WAIT_EVENT_DATA_FILE_WRITE);
+
+	TRACE_POSTGRESQL_SMGR_MD_WRITE_DONE(forknum, blocknum,
+										reln->smgr_rnode.node.spcNode,
+										reln->smgr_rnode.node.dbNode,
+										reln->smgr_rnode.node.relNode,
+										reln->smgr_rnode.backend,
+										nbytes,
+										BLCKSZ);
+
+	if (nbytes != BLCKSZ)
+	{
+		if (nbytes < 0)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not write block %u in file \"%s\": %m",
+							blocknum, FilePathName(v->mdfd_vfd))));
+		/* short write: complain appropriately */
+		ereport(ERROR,
+				(errcode(ERRCODE_DISK_FULL),
+				 errmsg("could not write block %u in file \"%s\": wrote only %d of %d bytes",
+						blocknum,
+						FilePathName(v->mdfd_vfd),
+						nbytes, BLCKSZ),
+				 errhint("Check free disk space.")));
+	}
+
+	if (!skipFsync && !SmgrIsTemp(reln))
+		register_dirty_segment(reln, forknum, v);
+}
+
+/*
+ *	mdnblocks() -- Get the number of blocks stored in a relation.
+ *
+ *		Important side effect: all active segments of the relation are opened
+ *		and added to the md_seg_fds array.  If this routine has not been
+ *		called, then only segments up to the last one actually touched
+ *		are present in the array.
+ */
+BlockNumber
+mdnblocks(SMgrRelation reln, ForkNumber forknum)
+{
+	MdfdVec    *v;
+	BlockNumber nblocks;
+	BlockNumber segno;
+
+	mdopenfork(reln, forknum, EXTENSION_FAIL);
+
+	/* mdopen has opened the first segment */
+	Assert(reln->md_num_open_segs[forknum] > 0);
+
+	/*
+	 * Start from the last open segments, to avoid redundant seeks.  We have
+	 * previously verified that these segments are exactly RELSEG_SIZE long,
+	 * and it's useless to recheck that each time.
+	 *
+	 * NOTE: this assumption could only be wrong if another backend has
+	 * truncated the relation.  We rely on higher code levels to handle that
+	 * scenario by closing and re-opening the md fd, which is handled via
+	 * relcache flush.  (Since the checkpointer doesn't participate in
+	 * relcache flush, it could have segment entries for inactive segments;
+	 * that's OK because the checkpointer never needs to compute relation
+	 * size.)
+	 */
+	segno = reln->md_num_open_segs[forknum] - 1;
+	v = &reln->md_seg_fds[forknum][segno];
+
+	for (;;)
+	{
+		nblocks = _mdnblocks(reln, forknum, v);
+		if (nblocks > ((BlockNumber) RELSEG_SIZE))
+			elog(FATAL, "segment too big");
+		if (nblocks < ((BlockNumber) RELSEG_SIZE))
+			return (segno * ((BlockNumber) RELSEG_SIZE)) + nblocks;
+
+		/*
+		 * If segment is exactly RELSEG_SIZE, advance to next one.
+		 */
+		segno++;
+
+		/*
+		 * We used to pass O_CREAT here, but that has the disadvantage that it
+		 * might create a segment which has vanished through some operating
+		 * system misadventure.  In such a case, creating the segment here
+		 * undermines _mdfd_getseg's attempts to notice and report an error
+		 * upon access to a missing segment.
+		 */
+		v = _mdfd_openseg(reln, forknum, segno, 0);
+		if (v == NULL)
+			return segno * ((BlockNumber) RELSEG_SIZE);
+	}
+}
+
+/*
+ *	mdtruncate() -- Truncate relation to specified number of blocks.
+ */
+void
+mdtruncate(SMgrRelation reln, ForkNumber forknum, BlockNumber nblocks)
+{
+	BlockNumber curnblk;
+	BlockNumber priorblocks;
+	int			curopensegs;
+
+	/*
+	 * NOTE: mdnblocks makes sure we have opened all active segments, so that
+	 * truncation loop will get them all!
+	 */
+	curnblk = mdnblocks(reln, forknum);
+	if (nblocks > curnblk)
+	{
+		/* Bogus request ... but no complaint if InRecovery */
+		if (InRecovery)
+			return;
+		ereport(ERROR,
+				(errmsg("could not truncate file \"%s\" to %u blocks: it's only %u blocks now",
+						relpath(reln->smgr_rnode, forknum),
+						nblocks, curnblk)));
+	}
+	if (nblocks == curnblk)
+		return;					/* no work */
+
+	/*
+	 * Truncate segments, starting at the last one. Starting at the end makes
+	 * managing the memory for the fd array easier, should there be errors.
+	 */
+	curopensegs = reln->md_num_open_segs[forknum];
+	while (curopensegs > 0)
+	{
+		MdfdVec    *v;
+
+		priorblocks = (curopensegs - 1) * RELSEG_SIZE;
+
+		v = &reln->md_seg_fds[forknum][curopensegs - 1];
+
+		if (priorblocks > nblocks)
+		{
+			/*
+			 * This segment is no longer active. We truncate the file, but do
+			 * not delete it, for reasons explained in the header comments.
+			 */
+			if (FileTruncate(v->mdfd_vfd, 0, WAIT_EVENT_DATA_FILE_TRUNCATE) < 0)
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not truncate file \"%s\": %m",
+								FilePathName(v->mdfd_vfd))));
+
+			if (!SmgrIsTemp(reln))
+				register_dirty_segment(reln, forknum, v);
+
+			/* we never drop the 1st segment */
+			Assert(v != &reln->md_seg_fds[forknum][0]);
+
+			FileClose(v->mdfd_vfd);
+			_fdvec_resize(reln, forknum, curopensegs - 1);
+		}
+		else if (priorblocks + ((BlockNumber) RELSEG_SIZE) > nblocks)
+		{
+			/*
+			 * This is the last segment we want to keep. Truncate the file to
+			 * the right length. NOTE: if nblocks is exactly a multiple K of
+			 * RELSEG_SIZE, we will truncate the K+1st segment to 0 length but
+			 * keep it. This adheres to the invariant given in the header
+			 * comments.
+			 */
+			BlockNumber lastsegblocks = nblocks - priorblocks;
+
+			if (FileTruncate(v->mdfd_vfd, (off_t) lastsegblocks * BLCKSZ, WAIT_EVENT_DATA_FILE_TRUNCATE) < 0)
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not truncate file \"%s\" to %u blocks: %m",
+								FilePathName(v->mdfd_vfd),
+								nblocks)));
+			if (!SmgrIsTemp(reln))
+				register_dirty_segment(reln, forknum, v);
+		}
+		else
+		{
+			/*
+			 * We still need this segment, so nothing to do for this and any
+			 * earlier segment.
+			 */
+			break;
+		}
+		curopensegs--;
+	}
+}
+
+/*
+ *	mdimmedsync() -- Immediately sync a relation to stable storage.
+ *
+ * Note that only writes already issued are synced; this routine knows
+ * nothing of dirty buffers that may exist inside the buffer manager.  We
+ * sync active and inactive segments; smgrDoPendingSyncs() relies on this.
+ * Consider a relation skipping WAL.  Suppose a checkpoint syncs blocks of
+ * some segment, then mdtruncate() renders that segment inactive.  If we
+ * crash before the next checkpoint syncs the newly-inactive segment, that
+ * segment may survive recovery, reintroducing unwanted data into the table.
+ */
+void
+mdimmedsync(SMgrRelation reln, ForkNumber forknum)
+{
+	int			segno;
+	int			min_inactive_seg;
+
+	/*
+	 * NOTE: mdnblocks makes sure we have opened all active segments, so that
+	 * fsync loop will get them all!
+	 */
+	mdnblocks(reln, forknum);
+
+	min_inactive_seg = segno = reln->md_num_open_segs[forknum];
+
+	/*
+	 * Temporarily open inactive segments, then close them after sync.  There
+	 * may be some inactive segments left opened after fsync() error, but that
+	 * is harmless.  We don't bother to clean them up and take a risk of
+	 * further trouble.  The next mdclose() will soon close them.
+	 */
+	while (_mdfd_openseg(reln, forknum, segno, 0) != NULL)
+		segno++;
+
+	while (segno > 0)
+	{
+		MdfdVec    *v = &reln->md_seg_fds[forknum][segno - 1];
+
+		if (FileSync(v->mdfd_vfd, WAIT_EVENT_DATA_FILE_IMMEDIATE_SYNC) < 0)
+			ereport(data_sync_elevel(ERROR),
+					(errcode_for_file_access(),
+					 errmsg("could not fsync file \"%s\": %m",
+							FilePathName(v->mdfd_vfd))));
+
+		/* Close inactive segments immediately */
+		if (segno > min_inactive_seg)
+		{
+			FileClose(v->mdfd_vfd);
+			_fdvec_resize(reln, forknum, segno - 1);
+		}
+
+		segno--;
+	}
+}
+
+/*
+ * register_dirty_segment() -- Mark a relation segment as needing fsync
+ *
+ * If there is a local pending-ops table, just make an entry in it for
+ * ProcessSyncRequests to process later.  Otherwise, try to pass off the
+ * fsync request to the checkpointer process.  If that fails, just do the
+ * fsync locally before returning (we hope this will not happen often
+ * enough to be a performance problem).
+ */
+static void
+register_dirty_segment(SMgrRelation reln, ForkNumber forknum, MdfdVec *seg)
+{
+	FileTag		tag;
+
+	INIT_MD_FILETAG(tag, reln->smgr_rnode.node, forknum, seg->mdfd_segno);
+
+	/* Temp relations should never be fsync'd */
+	Assert(!SmgrIsTemp(reln));
+
+	if (!RegisterSyncRequest(&tag, SYNC_REQUEST, false /* retryOnError */ ))
+	{
+		ereport(DEBUG1,
+				(errmsg_internal("could not forward fsync request because request queue is full")));
+
+		if (FileSync(seg->mdfd_vfd, WAIT_EVENT_DATA_FILE_SYNC) < 0)
+			ereport(data_sync_elevel(ERROR),
+					(errcode_for_file_access(),
+					 errmsg("could not fsync file \"%s\": %m",
+							FilePathName(seg->mdfd_vfd))));
+	}
+}
+
+/*
+ * register_unlink_segment() -- Schedule a file to be deleted after next checkpoint
+ */
+static void
+register_unlink_segment(RelFileNodeBackend rnode, ForkNumber forknum,
+						BlockNumber segno)
+{
+	FileTag		tag;
+
+	INIT_MD_FILETAG(tag, rnode.node, forknum, segno);
+
+	/* Should never be used with temp relations */
+	Assert(!RelFileNodeBackendIsTemp(rnode));
+
+	RegisterSyncRequest(&tag, SYNC_UNLINK_REQUEST, true /* retryOnError */ );
+}
+
+/*
+ * register_forget_request() -- forget any fsyncs for a relation fork's segment
+ */
+static void
+register_forget_request(RelFileNodeBackend rnode, ForkNumber forknum,
+						BlockNumber segno)
+{
+	FileTag		tag;
+
+	INIT_MD_FILETAG(tag, rnode.node, forknum, segno);
+
+	RegisterSyncRequest(&tag, SYNC_FORGET_REQUEST, true /* retryOnError */ );
+}
+
+/*
+ * ForgetDatabaseSyncRequests -- forget any fsyncs and unlinks for a DB
+ */
+void
+ForgetDatabaseSyncRequests(Oid dbid)
+{
+	FileTag		tag;
+	RelFileNode rnode;
+
+	rnode.dbNode = dbid;
+	rnode.spcNode = 0;
+	rnode.relNode = 0;
+
+	INIT_MD_FILETAG(tag, rnode, InvalidForkNumber, InvalidBlockNumber);
+
+	RegisterSyncRequest(&tag, SYNC_FILTER_REQUEST, true /* retryOnError */ );
+}
+
+/*
+ * DropRelationFiles -- drop files of all given relations
+ */
+void
+DropRelationFiles(RelFileNode *delrels, int ndelrels, bool isRedo)
+{
+	SMgrRelation *srels;
+	int			i;
+
+	srels = palloc(sizeof(SMgrRelation) * ndelrels);
+	for (i = 0; i < ndelrels; i++)
+	{
+		SMgrRelation srel = smgropen(delrels[i], InvalidBackendId);
+
+		if (isRedo)
+		{
+			ForkNumber	fork;
+
+			for (fork = 0; fork <= MAX_FORKNUM; fork++)
+				XLogDropRelation(delrels[i], fork);
+		}
+		srels[i] = srel;
+	}
+
+	smgrdounlinkall(srels, ndelrels, isRedo);
+
+	for (i = 0; i < ndelrels; i++)
+		smgrclose(srels[i]);
+	pfree(srels);
+}
+
+
+/*
+ *	_fdvec_resize() -- Resize the fork's open segments array
+ */
+static void
+_fdvec_resize(SMgrRelation reln,
+			  ForkNumber forknum,
+			  int nseg)
+{
+	if (nseg == 0)
+	{
+		if (reln->md_num_open_segs[forknum] > 0)
+		{
+			pfree(reln->md_seg_fds[forknum]);
+			reln->md_seg_fds[forknum] = NULL;
+		}
+	}
+	else if (reln->md_num_open_segs[forknum] == 0)
+	{
+		reln->md_seg_fds[forknum] =
+			MemoryContextAlloc(MdCxt, sizeof(MdfdVec) * nseg);
+	}
+	else
+	{
+		/*
+		 * It doesn't seem worthwhile complicating the code to amortize
+		 * repalloc() calls.  Those are far faster than PathNameOpenFile() or
+		 * FileClose(), and the memory context internally will sometimes avoid
+		 * doing an actual reallocation.
+		 */
+		reln->md_seg_fds[forknum] =
+			repalloc(reln->md_seg_fds[forknum],
+					 sizeof(MdfdVec) * nseg);
+	}
+
+	reln->md_num_open_segs[forknum] = nseg;
+}
+
+/*
+ * Return the filename for the specified segment of the relation. The
+ * returned string is palloc'd.
+ */
+static char *
+_mdfd_segpath(SMgrRelation reln, ForkNumber forknum, BlockNumber segno)
+{
+	char	   *path,
+			   *fullpath;
+
+	path = relpath(reln->smgr_rnode, forknum);
+
+	if (segno > 0)
+	{
+		fullpath = psprintf("%s.%u", path, segno);
+		pfree(path);
+	}
+	else
+		fullpath = path;
+
+	return fullpath;
+}
+
+/*
+ * Open the specified segment of the relation,
+ * and make a MdfdVec object for it.  Returns NULL on failure.
+ */
+static MdfdVec *
+_mdfd_openseg(SMgrRelation reln, ForkNumber forknum, BlockNumber segno,
+			  int oflags)
+{
+	MdfdVec    *v;
+	File		fd;
+	char	   *fullpath;
+
+	fullpath = _mdfd_segpath(reln, forknum, segno);
+
+	/* open the file */
+	fd = PathNameOpenFile(fullpath, O_RDWR | PG_BINARY | oflags);
+
+	pfree(fullpath);
+
+	if (fd < 0)
+		return NULL;
+
+	/*
+	 * Segments are always opened in order from lowest to highest, so we must
+	 * be adding a new one at the end.
+	 */
+	Assert(segno == reln->md_num_open_segs[forknum]);
+
+	_fdvec_resize(reln, forknum, segno + 1);
+
+	/* fill the entry */
+	v = &reln->md_seg_fds[forknum][segno];
+	v->mdfd_vfd = fd;
+	v->mdfd_segno = segno;
+
+	Assert(_mdnblocks(reln, forknum, v) <= ((BlockNumber) RELSEG_SIZE));
+
+	/* all done */
+	return v;
+}
+
+/*
+ *	_mdfd_getseg() -- Find the segment of the relation holding the
+ *		specified block.
+ *
+ * If the segment doesn't exist, we ereport, return NULL, or create the
+ * segment, according to "behavior".  Note: skipFsync is only used in the
+ * EXTENSION_CREATE case.
+ */
+static MdfdVec *
+_mdfd_getseg(SMgrRelation reln, ForkNumber forknum, BlockNumber blkno,
+			 bool skipFsync, int behavior)
+{
+	MdfdVec    *v;
+	BlockNumber targetseg;
+	BlockNumber nextsegno;
+
+	/* some way to handle non-existent segments needs to be specified */
+	Assert(behavior &
+		   (EXTENSION_FAIL | EXTENSION_CREATE | EXTENSION_RETURN_NULL));
+
+	targetseg = blkno / ((BlockNumber) RELSEG_SIZE);
+
+	/* if an existing and opened segment, we're done */
+	if (targetseg < reln->md_num_open_segs[forknum])
+	{
+		v = &reln->md_seg_fds[forknum][targetseg];
+		return v;
+	}
+
+	/*
+	 * The target segment is not yet open. Iterate over all the segments
+	 * between the last opened and the target segment. This way missing
+	 * segments either raise an error, or get created (according to
+	 * 'behavior'). Start with either the last opened, or the first segment if
+	 * none was opened before.
+	 */
+	if (reln->md_num_open_segs[forknum] > 0)
+		v = &reln->md_seg_fds[forknum][reln->md_num_open_segs[forknum] - 1];
+	else
+	{
+		v = mdopenfork(reln, forknum, behavior);
+		if (!v)
+			return NULL;		/* if behavior & EXTENSION_RETURN_NULL */
+	}
+
+	for (nextsegno = reln->md_num_open_segs[forknum];
+		 nextsegno <= targetseg; nextsegno++)
+	{
+		BlockNumber nblocks = _mdnblocks(reln, forknum, v);
+		int			flags = 0;
+
+		Assert(nextsegno == v->mdfd_segno + 1);
+
+		if (nblocks > ((BlockNumber) RELSEG_SIZE))
+			elog(FATAL, "segment too big");
+
+		if ((behavior & EXTENSION_CREATE) ||
+			(InRecovery && (behavior & EXTENSION_CREATE_RECOVERY)))
+		{
+			/*
+			 * Normally we will create new segments only if authorized by the
+			 * caller (i.e., we are doing mdextend()).  But when doing WAL
+			 * recovery, create segments anyway; this allows cases such as
+			 * replaying WAL data that has a write into a high-numbered
+			 * segment of a relation that was later deleted. We want to go
+			 * ahead and create the segments so we can finish out the replay.
+			 *
+			 * We have to maintain the invariant that segments before the last
+			 * active segment are of size RELSEG_SIZE; therefore, if
+			 * extending, pad them out with zeroes if needed.  (This only
+			 * matters if in recovery, or if the caller is extending the
+			 * relation discontiguously, but that can happen in hash indexes.)
+			 */
+			if (nblocks < ((BlockNumber) RELSEG_SIZE))
+			{
+				char	   *zerobuf = palloc0(BLCKSZ);
+
+				mdextend(reln, forknum,
+						 nextsegno * ((BlockNumber) RELSEG_SIZE) - 1,
+						 zerobuf, skipFsync);
+				pfree(zerobuf);
+			}
+			flags = O_CREAT;
+		}
+		else if (!(behavior & EXTENSION_DONT_CHECK_SIZE) &&
+				 nblocks < ((BlockNumber) RELSEG_SIZE))
+		{
+			/*
+			 * When not extending (or explicitly including truncated
+			 * segments), only open the next segment if the current one is
+			 * exactly RELSEG_SIZE.  If not (this branch), either return NULL
+			 * or fail.
+			 */
+			if (behavior & EXTENSION_RETURN_NULL)
+			{
+				/*
+				 * Some callers discern between reasons for _mdfd_getseg()
+				 * returning NULL based on errno. As there's no failing
+				 * syscall involved in this case, explicitly set errno to
+				 * ENOENT, as that seems the closest interpretation.
+				 */
+				errno = ENOENT;
+				return NULL;
+			}
+
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not open file \"%s\" (target block %u): previous segment is only %u blocks",
+							_mdfd_segpath(reln, forknum, nextsegno),
+							blkno, nblocks)));
+		}
+
+		v = _mdfd_openseg(reln, forknum, nextsegno, flags);
+
+		if (v == NULL)
+		{
+			if ((behavior & EXTENSION_RETURN_NULL) &&
+				FILE_POSSIBLY_DELETED(errno))
+				return NULL;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not open file \"%s\" (target block %u): %m",
+							_mdfd_segpath(reln, forknum, nextsegno),
+							blkno)));
+		}
+	}
+
+	return v;
+}
+
+/*
+ * Get number of blocks present in a single disk file
+ */
+static BlockNumber
+_mdnblocks(SMgrRelation reln, ForkNumber forknum, MdfdVec *seg)
+{
+	off_t		len;
+
+	len = FileSize(seg->mdfd_vfd);
+	if (len < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not seek to end of file \"%s\": %m",
+						FilePathName(seg->mdfd_vfd))));
+	/* note that this calculation will ignore any partial block at EOF */
+	return (BlockNumber) (len / BLCKSZ);
+}
+
+/*
+ * Sync a file to disk, given a file tag.  Write the path into an output
+ * buffer so the caller can use it in error messages.
+ *
+ * Return 0 on success, -1 on failure, with errno set.
+ */
+int
+mdsyncfiletag(const FileTag *ftag, char *path)
+{
+	SMgrRelation reln = smgropen(ftag->rnode, InvalidBackendId);
+	File		file;
+	bool		need_to_close;
+	int			result,
+				save_errno;
+
+	/* See if we already have the file open, or need to open it. */
+	if (ftag->segno < reln->md_num_open_segs[ftag->forknum])
+	{
+		file = reln->md_seg_fds[ftag->forknum][ftag->segno].mdfd_vfd;
+		strlcpy(path, FilePathName(file), MAXPGPATH);
+		need_to_close = false;
+	}
+	else
+	{
+		char	   *p;
+
+		p = _mdfd_segpath(reln, ftag->forknum, ftag->segno);
+		strlcpy(path, p, MAXPGPATH);
+		pfree(p);
+
+		file = PathNameOpenFile(path, O_RDWR | PG_BINARY);
+		if (file < 0)
+			return -1;
+		need_to_close = true;
+	}
+
+	/* Sync the file. */
+	result = FileSync(file, WAIT_EVENT_DATA_FILE_SYNC);
+	save_errno = errno;
+
+	if (need_to_close)
+		FileClose(file);
+
+	errno = save_errno;
+	return result;
+}
+
+/*
+ * Unlink a file, given a file tag.  Write the path into an output
+ * buffer so the caller can use it in error messages.
+ *
+ * Return 0 on success, -1 on failure, with errno set.
+ */
+int
+mdunlinkfiletag(const FileTag *ftag, char *path)
+{
+	char	   *p;
+
+	/* Compute the path. */
+	p = relpathperm(ftag->rnode, MAIN_FORKNUM);
+	strlcpy(path, p, MAXPGPATH);
+	pfree(p);
+
+	/* Try to unlink the file. */
+	return unlink(path);
+}
+
+/*
+ * Check if a given candidate request matches a given tag, when processing
+ * a SYNC_FILTER_REQUEST request.  This will be called for all pending
+ * requests to find out whether to forget them.
+ */
+bool
+mdfiletagmatches(const FileTag *ftag, const FileTag *candidate)
+{
+	/*
+	 * For now we only use filter requests as a way to drop all scheduled
+	 * callbacks relating to a given database, when dropping the database.
+	 * We'll return true for all candidates that have the same database OID as
+	 * the ftag from the SYNC_FILTER_REQUEST request, so they're forgotten.
+	 */
+	return ftag->rnode.dbNode == candidate->rnode.dbNode;
+}