From 45e191e3aa62d47a8bc1a33f784286b2051f45cb Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Thu, 8 Sep 2016 17:02:43 -0700
Subject: [PATCH] Improve scalability of md.c for large relations.
So far md.c used a linked list of segments. That proved to be a problem
when processing large relations, because every smgr.c/md.c level access
to a page incurred walking through a linked list of all preceding
segments. Thus making accessing pages O(#segments).
Replace the linked list of segments hanging off SMgrRelationData with an
array of opened segments. That allows O(1) access to individual
segments, if they've previously been opened.
Discussion: <20140331101001.GE13135@alap3.anarazel.de>
Reviewed-By: Peter Geoghegan, Tom Lane (in an older version)
---
src/backend/storage/smgr/md.c | 393 ++++++++++++++++++--------------
src/backend/storage/smgr/smgr.c | 4 +-
src/include/storage/smgr.h | 8 +-
3 files changed, 229 insertions(+), 176 deletions(-)
diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index a94828b32c7..1360f773df1 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -92,27 +92,23 @@
* out to an unlinked old copy of a segment file that will eventually
* disappear.
*
- * The file descriptor pointer (md_fd field) stored in the SMgrRelation
- * cache is, therefore, just the head of a list of MdfdVec objects, one
- * per segment. But note the md_fd pointer can be NULL, indicating
- * relation not open.
- *
- * Also note that mdfd_chain == NULL does not necessarily mean the relation
- * doesn't have another segment after this one; we may just not have
- * opened the next segment yet. (We could not have "all segments are
- * in the chain" as an invariant anyway, since another backend could
- * extend the relation when we weren't looking.) We do not make chain
+ * 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.
*
- * All MdfdVec objects are palloc'd in the MdCxt memory context.
+ * 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 */
- struct _MdfdVec *mdfd_chain; /* next segment, or NULL */
} MdfdVec;
static MemoryContext MdCxt; /* context for all MdfdVec objects */
@@ -189,7 +185,9 @@ static MdfdVec *mdopen(SMgrRelation reln, ForkNumber forknum, int behavior);
static void register_dirty_segment(SMgrRelation reln, ForkNumber forknum,
MdfdVec *seg);
static void register_unlink(RelFileNodeBackend rnode);
-static MdfdVec *_fdvec_alloc(void);
+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,
@@ -294,13 +292,14 @@ mdexists(SMgrRelation reln, ForkNumber forkNum)
void
mdcreate(SMgrRelation reln, ForkNumber forkNum, bool isRedo)
{
+ MdfdVec *mdfd;
char *path;
File fd;
- if (isRedo && reln->md_fd[forkNum] != NULL)
+ if (isRedo && reln->md_num_open_segs[forkNum] > 0)
return; /* created and opened already... */
- Assert(reln->md_fd[forkNum] == NULL);
+ Assert(reln->md_num_open_segs[forkNum] == 0);
path = relpath(reln->smgr_rnode, forkNum);
@@ -330,11 +329,10 @@ mdcreate(SMgrRelation reln, ForkNumber forkNum, bool isRedo)
pfree(path);
- reln->md_fd[forkNum] = _fdvec_alloc();
-
- reln->md_fd[forkNum]->mdfd_vfd = fd;
- reln->md_fd[forkNum]->mdfd_segno = 0;
- reln->md_fd[forkNum]->mdfd_chain = NULL;
+ _fdvec_resize(reln, forkNum, 1);
+ mdfd = &reln->md_seg_fds[forkNum][0];
+ mdfd->mdfd_vfd = fd;
+ mdfd->mdfd_segno = 0;
}
/*
@@ -579,8 +577,8 @@ mdopen(SMgrRelation reln, ForkNumber forknum, int behavior)
File fd;
/* No work if already open */
- if (reln->md_fd[forknum])
- return reln->md_fd[forknum];
+ if (reln->md_num_open_segs[forknum] > 0)
+ return &reln->md_seg_fds[forknum][0];
path = relpath(reln->smgr_rnode, forknum);
@@ -612,11 +610,11 @@ mdopen(SMgrRelation reln, ForkNumber forknum, int behavior)
pfree(path);
- reln->md_fd[forknum] = mdfd = _fdvec_alloc();
-
+ _fdvec_resize(reln, forknum, 1);
+ mdfd = &reln->md_seg_fds[forknum][0];
mdfd->mdfd_vfd = fd;
mdfd->mdfd_segno = 0;
- mdfd->mdfd_chain = NULL;
+
Assert(_mdnblocks(reln, forknum, mdfd) <= ((BlockNumber) RELSEG_SIZE));
return mdfd;
@@ -628,25 +626,29 @@ mdopen(SMgrRelation reln, ForkNumber forknum, int behavior)
void
mdclose(SMgrRelation reln, ForkNumber forknum)
{
- MdfdVec *v = reln->md_fd[forknum];
+ int nopensegs = reln->md_num_open_segs[forknum];
/* No work if already closed */
- if (v == NULL)
+ if (nopensegs == 0)
return;
- reln->md_fd[forknum] = NULL; /* prevent dangling pointer after error */
-
- while (v != NULL)
+ /* close segments starting from the end */
+ while (nopensegs > 0)
{
- MdfdVec *ov = v;
+ MdfdVec *v = &reln->md_seg_fds[forknum][nopensegs - 1];
/* if not closed already */
if (v->mdfd_vfd >= 0)
+ {
FileClose(v->mdfd_vfd);
- /* Now free vector */
- v = v->mdfd_chain;
- pfree(ov);
+ v->mdfd_vfd = -1;
+ }
+
+ nopensegs--;
}
+
+ /* resize just once, avoids pointless reallocations */
+ _fdvec_resize(reln, forknum, 0);
}
/*
@@ -862,9 +864,9 @@ mdwrite(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
* 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 mdfd_chain list. If this routine has not been
+ * and added to the mdfd_seg_fds array. If this routine has not been
* called, then only segments up to the last one actually touched
- * are present in the chain.
+ * are present in the array.
*/
BlockNumber
mdnblocks(SMgrRelation reln, ForkNumber forknum)
@@ -873,24 +875,24 @@ mdnblocks(SMgrRelation reln, ForkNumber forknum)
BlockNumber nblocks;
BlockNumber segno = 0;
+ /* mdopen has opened the first segment */
+ Assert(reln->md_num_open_segs[forknum] > 0);
+
/*
- * Skip through any segments that aren't the last one, to avoid redundant
- * seeks on them. We have previously verified that these segments are
- * exactly RELSEG_SIZE long, and it's useless to recheck that each time.
+ * 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 chain entries for inactive
- * segments; that's OK because the checkpointer never needs to compute
- * relation size.)
+ * relcache flush, it could have segment entries for inactive segments;
+ * that's OK because the checkpointer never needs to compute relation
+ * size.)
*/
- while (v->mdfd_chain != NULL)
- {
- segno++;
- v = v->mdfd_chain;
- }
+ segno = reln->md_num_open_segs[forknum] - 1;
+ v = &reln->md_seg_fds[forknum][segno];
for (;;)
{
@@ -905,21 +907,16 @@ mdnblocks(SMgrRelation reln, ForkNumber forknum)
*/
segno++;
- if (v->mdfd_chain == NULL)
- {
- /*
- * We used to pass O_CREAT here, but that's 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_chain = _mdfd_openseg(reln, forknum, segno, 0);
- if (v->mdfd_chain == NULL)
- return segno * ((BlockNumber) RELSEG_SIZE);
- }
-
- v = v->mdfd_chain;
+ /*
+ * We used to pass O_CREAT here, but that's 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);
}
}
@@ -929,9 +926,9 @@ mdnblocks(SMgrRelation reln, ForkNumber forknum)
void
mdtruncate(SMgrRelation reln, ForkNumber forknum, BlockNumber nblocks)
{
- MdfdVec *v;
BlockNumber curnblk;
BlockNumber priorblocks;
+ int curopensegs;
/*
* NOTE: mdnblocks makes sure we have opened all active segments, so that
@@ -951,19 +948,24 @@ mdtruncate(SMgrRelation reln, ForkNumber forknum, BlockNumber nblocks)
if (nblocks == curnblk)
return; /* no work */
- v = mdopen(reln, forknum, EXTENSION_FAIL);
-
- priorblocks = 0;
- while (v != NULL)
+ /*
+ * 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 *ov = v;
+ MdfdVec *v;
+
+ priorblocks = (curopensegs - 1) * RELSEG_SIZE;
+
+ v = &reln->md_seg_fds[forknum][curopensegs - 1];
if (priorblocks > nblocks)
{
/*
- * This segment is no longer active (and has already been unlinked
- * from the mdfd_chain). We truncate the file, but do not delete
- * it, for reasons explained in the header comments.
+ * 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) < 0)
ereport(ERROR,
@@ -973,21 +975,21 @@ mdtruncate(SMgrRelation reln, ForkNumber forknum, BlockNumber nblocks)
if (!SmgrIsTemp(reln))
register_dirty_segment(reln, forknum, v);
- v = v->mdfd_chain;
- Assert(ov != reln->md_fd[forknum]); /* we never drop the 1st
- * segment */
- FileClose(ov->mdfd_vfd);
- pfree(ov);
+
+ /* 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, and clear chain link that points to any
- * remaining segments (which we shall zap). 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.
+ * 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;
@@ -999,18 +1001,16 @@ mdtruncate(SMgrRelation reln, ForkNumber forknum, BlockNumber nblocks)
nblocks)));
if (!SmgrIsTemp(reln))
register_dirty_segment(reln, forknum, v);
- v = v->mdfd_chain;
- ov->mdfd_chain = NULL;
}
else
{
/*
- * We still need this segment and 0 or more blocks beyond it, so
- * nothing to do here.
+ * We still need this segment, so nothing to do for this and any
+ * earlier segment.
*/
- v = v->mdfd_chain;
+ break;
}
- priorblocks += RELSEG_SIZE;
+ curopensegs--;
}
}
@@ -1023,7 +1023,7 @@ mdtruncate(SMgrRelation reln, ForkNumber forknum, BlockNumber nblocks)
void
mdimmedsync(SMgrRelation reln, ForkNumber forknum)
{
- MdfdVec *v;
+ int segno;
/*
* NOTE: mdnblocks makes sure we have opened all active segments, so that
@@ -1031,16 +1031,18 @@ mdimmedsync(SMgrRelation reln, ForkNumber forknum)
*/
mdnblocks(reln, forknum);
- v = mdopen(reln, forknum, EXTENSION_FAIL);
+ segno = reln->md_num_open_segs[forknum];
- while (v != NULL)
+ while (segno > 0)
{
+ MdfdVec *v = &reln->md_seg_fds[forknum][segno - 1];
+
if (FileSync(v->mdfd_vfd) < 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not fsync file \"%s\": %m",
FilePathName(v->mdfd_vfd))));
- v = v->mdfd_chain;
+ segno--;
}
}
@@ -1703,12 +1705,40 @@ ForgetDatabaseFsyncRequests(Oid dbid)
/*
- * _fdvec_alloc() -- Make a MdfdVec object.
+ * _fdvec_resize() -- Resize the fork's open segments array
*/
-static MdfdVec *
-_fdvec_alloc(void)
+static void
+_fdvec_resize(SMgrRelation reln,
+ ForkNumber forknum,
+ int nseg)
{
- return (MdfdVec *) MemoryContextAlloc(MdCxt, sizeof(MdfdVec));
+ 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 worthwile complicating the code by having a more
+ * aggressive growth strategy here; the number of segments doesn't
+ * grow that fast, 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;
}
/*
@@ -1756,13 +1786,14 @@ _mdfd_openseg(SMgrRelation reln, ForkNumber forknum, BlockNumber segno,
if (fd < 0)
return NULL;
- /* allocate an mdfdvec entry for it */
- v = _fdvec_alloc();
+ if (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;
- v->mdfd_chain = NULL;
+
Assert(_mdnblocks(reln, forknum, v) <= ((BlockNumber) RELSEG_SIZE));
/* all done */
@@ -1781,7 +1812,7 @@ static MdfdVec *
_mdfd_getseg(SMgrRelation reln, ForkNumber forknum, BlockNumber blkno,
bool skipFsync, int behavior)
{
- MdfdVec *v = mdopen(reln, forknum, behavior);
+ MdfdVec *v;
BlockNumber targetseg;
BlockNumber nextsegno;
@@ -1789,98 +1820,116 @@ _mdfd_getseg(SMgrRelation reln, ForkNumber forknum, BlockNumber blkno,
Assert(behavior &
(EXTENSION_FAIL | EXTENSION_CREATE | EXTENSION_RETURN_NULL));
- if (!v)
- return NULL; /* if behavior & EXTENSION_RETURN_NULL */
-
targetseg = blkno / ((BlockNumber) RELSEG_SIZE);
- for (nextsegno = 1; nextsegno <= targetseg; nextsegno++)
+
+ /* if an existing and opened segment, we're done */
+ if (targetseg < reln->md_num_open_segs[forknum])
{
- Assert(nextsegno == v->mdfd_segno + 1);
+ v = &reln->md_seg_fds[forknum][targetseg];
+ return v;
+ }
- if (v->mdfd_chain == NULL)
- {
- BlockNumber nblocks = _mdnblocks(reln, forknum, v);
- int flags = 0;
+ /*
+ * 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 = mdopen(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;
- if (nblocks > ((BlockNumber) RELSEG_SIZE))
- elog(FATAL, "segment too big");
+ 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)))
+ 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.
+ * However if the caller has specified
+ * EXTENSION_REALLY_RETURN_NULL, then extension is not desired
+ * even in recovery; we won't reach this point in that case.
+ *
+ * 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))
{
- /*
- * 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. However if the caller has specified
- * EXTENSION_REALLY_RETURN_NULL, then extension is not desired
- * even in recovery; we won't reach this point in that case.
- *
- * 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);
+ char *zerobuf = palloc0(BLCKSZ);
- mdextend(reln, forknum,
- nextsegno * ((BlockNumber) RELSEG_SIZE) - 1,
- zerobuf, skipFsync);
- pfree(zerobuf);
- }
- flags = O_CREAT;
+ mdextend(reln, forknum,
+ nextsegno * ((BlockNumber) RELSEG_SIZE) - 1,
+ zerobuf, skipFsync);
+ pfree(zerobuf);
}
- else if (!(behavior & EXTENSION_DONT_CHECK_SIZE) &&
- nblocks < ((BlockNumber) RELSEG_SIZE))
+ 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)
{
/*
- * 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.
+ * 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.
*/
- 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)));
+ errno = ENOENT;
+ return NULL;
}
- v->mdfd_chain = _mdfd_openseg(reln, forknum, nextsegno, flags);
+ 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)));
+ }
- if (v->mdfd_chain == NULL)
- {
- if ((behavior & EXTENSION_RETURN_NULL) &&
- FILE_POSSIBLY_DELETED(errno))
- return NULL;
- ereport(ERROR,
- (errcode_for_file_access(),
+ 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)));
- }
}
- v = v->mdfd_chain;
}
+
return v;
}
diff --git a/src/backend/storage/smgr/smgr.c b/src/backend/storage/smgr/smgr.c
index 94aa952bcc8..93f0080a60c 100644
--- a/src/backend/storage/smgr/smgr.c
+++ b/src/backend/storage/smgr/smgr.c
@@ -174,7 +174,7 @@ smgropen(RelFileNode rnode, BackendId backend)
/* mark it not open */
for (forknum = 0; forknum <= MAX_FORKNUM; forknum++)
- reln->md_fd[forknum] = NULL;
+ reln->md_num_open_segs[forknum] = 0;
/* it has no owner yet */
add_to_unowned_list(reln);
@@ -379,7 +379,7 @@ smgrcreate(SMgrRelation reln, ForkNumber forknum, bool isRedo)
* Exit quickly in WAL replay mode if we've already opened the file. If
* it's open, it surely must exist.
*/
- if (isRedo && reln->md_fd[forknum] != NULL)
+ if (isRedo && reln->md_num_open_segs[forknum] > 0)
return;
/*
diff --git a/src/include/storage/smgr.h b/src/include/storage/smgr.h
index a8e7877f704..3430d8665e4 100644
--- a/src/include/storage/smgr.h
+++ b/src/include/storage/smgr.h
@@ -64,8 +64,12 @@ typedef struct SMgrRelationData
*/
int smgr_which; /* storage manager selector */
- /* for md.c; NULL for forks that are not open */
- struct _MdfdVec *md_fd[MAX_FORKNUM + 1];
+ /*
+ * for md.c; per-fork arrays of the number of open segments
+ * (md_num_open_segs) and the segments themselves (md_seg_fds).
+ */
+ int md_num_open_segs[MAX_FORKNUM + 1];
+ struct _MdfdVec *md_seg_fds[MAX_FORKNUM + 1];
/* if unowned, list link in list of all unowned SMgrRelations */
struct SMgrRelationData *next_unowned_reln;
--
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