upstream/postgresql
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2026-05-27 20:27:28 -04:00
Code Issues Projects Releases Packages Wiki Activity Actions

Update FSM during prune/freeze replay even if freespace is zero

Browse source 
add323da40 started updating the visibility map in the same WAL record
as pruning and freezing. This included updating the freespace map during
replay of a record setting the VM, which we've done since ab7dbd681.

add323da40, however, conditioned doing so on there being > 0 freespace
on the page, which differed from the previous state for records updating
the VM.

The FSM is not WAL-logged and is instead updated heuristically on
standbys. In rare cases, this heuristic could lead to pages with 0
freespace having outdated entries in the FSM. If the standby is later
promoted and vacuum skips these pages because they are marked
all-visible/all-frozen, overly optimistic values would be propagated up
the FSM tree, causing slowness when searching for freespace for new
tuples.

Fix it by always updating the FSM during replay when setting VM bits.

Author: Melanie Plageman <melanieplageman@gmail.com>
Reported-by: Alexey Makhmutov <a.makhmutov@postgrespro.ru>
Discussion: https://postgr.es/m/ead2f110-c736-48f5-99e1-023dc9acbf0b%40postgrespro.ru
This commit is contained in:
Melanie Plageman 2026-04-16 12:10:47 -04:00
parent af1ed03739
commit b4c1b2be30
1 changed files with 5 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

6
src/backend/access/heap/heapam_xlog.c
View file

@ -38,6 +38,7 @@ heap_xlog_prune_freeze(XLogReaderState *record)
Buffer vmbuffer = InvalidBuffer;
uint8 vmflags = 0;
Size freespace = 0;
bool do_update_fsm = false;
XLogRecGetBlockTag(record, 0, &rlocator, NULL, &blkno);
memcpy(&xlrec, maindataptr, SizeOfHeapPrune);
@ -211,7 +212,10 @@ heap_xlog_prune_freeze(XLogReaderState *record)
XLHP_HAS_DEAD_ITEMS |
XLHP_HAS_NOW_UNUSED_ITEMS)) ||
(vmflags & VISIBILITYMAP_VALID_BITS))
{
freespace = PageGetHeapFreeSpace(BufferGetPage(buffer));
do_update_fsm = true;
}
/*
* We want to avoid holding an exclusive lock on the heap buffer while
@ -248,7 +252,7 @@ heap_xlog_prune_freeze(XLogReaderState *record)
if (BufferIsValid(vmbuffer))
UnlockReleaseBuffer(vmbuffer);
if (freespace > 0)
if (do_update_fsm)
XLogRecordPageWithFreeSpace(rlocator, blkno, freespace);
}