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WAL log VM setting for empty pages in XLOG_HEAP2_PRUNE_VACUUM_SCAN

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As part of removing XLOG_HEAP2_VISIBLE records, phase I of VACUUM now
marks empty pages all-visible and all-frozen in a
XLOG_HEAP2_PRUNE_VACUUM_SCAN record.

This has no real independent benefit, but empty pages were the last user
of XLOG_HEAP2_VISIBLE, so by making this change we can next remove all
of the XLOG_HEAP2_VISIBLE code.

Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Kirill Reshke <reshkekirill@gmail.com>
Earlier version Reviewed-by: Robert Haas <robertmhaas@gmail.com>
This commit is contained in:
Melanie Plageman 2026-03-24 17:28:05 -04:00
parent 1252a4ee28
commit a759ced2f1
2 changed files with 50 additions and 29 deletions
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33
src/backend/access/heap/pruneheap.c
View file

@ -2541,6 +2541,8 @@ log_heap_prune_and_freeze(Relation relation, Buffer buffer,
uint8 info;
uint8 regbuf_flags_heap;
Page heap_page = BufferGetPage(buffer);
/* The following local variables hold data registered in the WAL record: */
xlhp_freeze_plan plans[MaxHeapTuplesPerPage];
xlhp_freeze_plans freeze_plans;
@ -2550,6 +2552,7 @@ log_heap_prune_and_freeze(Relation relation, Buffer buffer,
OffsetNumber frz_offsets[MaxHeapTuplesPerPage];
bool do_prune = nredirected > 0 || ndead > 0 || nunused > 0;
bool do_set_vm = vmflags & VISIBILITYMAP_VALID_BITS;
bool heap_fpi_allowed = true;
Assert((vmflags & VISIBILITYMAP_VALID_BITS) == vmflags);
@ -2559,15 +2562,22 @@ log_heap_prune_and_freeze(Relation relation, Buffer buffer,
/*
* We can avoid an FPI of the heap page if the only modification we are
* making to it is to set PD_ALL_VISIBLE and checksums/wal_log_hints are
* disabled. Note that if we explicitly skip an FPI, we must not stamp the
* heap page with this record's LSN. Recovery skips records <= the stamped
* LSN, so this could lead to skipping an earlier FPI needed to repair a
* torn page.
* disabled.
*
* However, if the page has never been WAL-logged (LSN is invalid), we
* must force an FPI regardless. This can happen when another backend
* extends the heap, initializes the page, and then fails before WAL-
* logging it. Since heap extension is not WAL-logged, recovery might try
* to replay our record and find that the page isn't initialized, which
* would cause a PANIC.
*/
if (!do_prune &&
nfrozen == 0 &&
(!do_set_vm || !XLogHintBitIsNeeded()))
if (!XLogRecPtrIsValid(PageGetLSN(heap_page)))
regbuf_flags_heap |= REGBUF_FORCE_IMAGE;
else if (!do_prune && nfrozen == 0 && (!do_set_vm || !XLogHintBitIsNeeded()))
{
regbuf_flags_heap |= REGBUF_NO_IMAGE;
heap_fpi_allowed = false;
}
/*
* Prepare data for the buffer. The arrays are not actually in the
@ -2681,12 +2691,13 @@ log_heap_prune_and_freeze(Relation relation, Buffer buffer,
}
/*
* See comment at the top of the function about regbuf_flags_heap for
* details on when we can advance the page LSN.
* If we explicitly skip an FPI, we must not stamp the heap page with this
* record's LSN. Recovery skips records <= the stamped LSN, so this could
* lead to skipping an earlier FPI needed to repair a torn page.
*/
if (do_prune || nfrozen > 0 || (do_set_vm && XLogHintBitIsNeeded()))
if (heap_fpi_allowed)
{
Assert(BufferIsDirty(buffer));
PageSetLSN(BufferGetPage(buffer), recptr);
PageSetLSN(heap_page, recptr);
}
}

46
src/backend/access/heap/vacuumlazy.c
View file

@ -1929,33 +1929,43 @@ lazy_scan_new_or_empty(LVRelState *vacrel, Buffer buf, BlockNumber blkno,
*/
if (!PageIsAllVisible(page))
{
/* Lock vmbuffer before entering critical section */
LockBuffer(vmbuffer, BUFFER_LOCK_EXCLUSIVE);
START_CRIT_SECTION();
/* mark buffer dirty before writing a WAL record */
MarkBufferDirty(buf);
/*
* It's possible that another backend has extended the heap,
* initialized the page, and then failed to WAL-log the page due
* to an ERROR. Since heap extension is not WAL-logged, recovery
* might try to replay our record setting the page all-visible and
* find that the page isn't initialized, which will cause a PANIC.
* To prevent that, check whether the page has been previously
* WAL-logged, and if not, do that now.
*/
if (RelationNeedsWAL(vacrel->rel) &&
!XLogRecPtrIsValid(PageGetLSN(page)))
log_newpage_buffer(buf, true);
PageSetAllVisible(page);
PageClearPrunable(page);
visibilitymap_set(vacrel->rel, blkno, buf,
InvalidXLogRecPtr,
vmbuffer, InvalidTransactionId,
VISIBILITYMAP_ALL_VISIBLE |
VISIBILITYMAP_ALL_FROZEN);
visibilitymap_set_vmbits(blkno,
vmbuffer,
VISIBILITYMAP_ALL_VISIBLE |
VISIBILITYMAP_ALL_FROZEN,
vacrel->rel->rd_locator);
/*
* Emit WAL for setting PD_ALL_VISIBLE on the heap page and
* setting the VM.
*/
if (RelationNeedsWAL(vacrel->rel))
log_heap_prune_and_freeze(vacrel->rel, buf,
vmbuffer,
VISIBILITYMAP_ALL_VISIBLE |
VISIBILITYMAP_ALL_FROZEN,
InvalidTransactionId, /* conflict xid */
false, /* cleanup lock */
PRUNE_VACUUM_SCAN, /* reason */
NULL, 0,
NULL, 0,
NULL, 0,
NULL, 0);
END_CRIT_SECTION();
LockBuffer(vmbuffer, BUFFER_LOCK_UNLOCK);
/* Count the newly all-frozen pages for logging */
vacrel->new_all_visible_pages++;
vacrel->new_all_visible_all_frozen_pages++;