From: Melanie Plageman Date: Thu, 16 Apr 2026 16:10:47 +0000 (-0400) Subject: Update FSM during prune/freeze replay even if freespace is zero X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b4c1b2be300e619aebc3a2c00198009af256bfee;p=thirdparty%2Fpostgresql.git Update FSM during prune/freeze replay even if freespace is zero add323da40a 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. add323da40a, 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 In rare cases, this heuristic could lead to pages with 0 freespace having outdated entries in the FSM.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 Reported-by: Alexey Makhmutov Discussion: https://postgr.es/m/ead2f110-c736-48f5-99e1-023dc9acbf0b%40postgrespro.ru --- diff --git a/src/backend/access/heap/heapam_xlog.c b/src/backend/access/heap/heapam_xlog.c index f3f419d3dc1..9ed7024e814 100644 --- a/src/backend/access/heap/heapam_xlog.c +++ b/src/backend/access/heap/heapam_xlog.c @@ -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); }