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Add comment about keeping PD_ALL_VISIBLE and VM in sync

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The comment above heap_xlog_visible() about the critical integrity
requirement for PD_ALL_VISIBLE and the visibility map should also be in
heap_xlog_prune_freeze() where we set PD_ALL_VISIBLE.

Oversight in add323da40

Author: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://postgr.es/m/flat/CAAKRu_ZMw6Npd_qm2KM%2BFwQ3cMOMx1Dh3VMhp8-V7SOLxdK9-g%40mail.gmail.com
This commit is contained in:
Melanie Plageman
2025-12-10 11:10:13 -05:00
parent bd298f54a0
commit eebec3ca4b
1 changed files with 6 additions and 0 deletions
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6
src/backend/access/heap/heapam_xlog.c
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@@ -157,6 +157,12 @@ heap_xlog_prune_freeze(XLogReaderState *record)
/* There should be no more data */ /* There should be no more data */
Assert((char *) frz_offsets == dataptr + datalen); Assert((char *) frz_offsets == dataptr + datalen);
/*
* The critical integrity requirement here is that we must never end
* up with the visibility map bit set and the page-level
* PD_ALL_VISIBLE bit unset. If that were to occur, a subsequent page
* modification would fail to clear the visibility map bit.
*/
if (vmflags & VISIBILITYMAP_VALID_BITS) if (vmflags & VISIBILITYMAP_VALID_BITS)
PageSetAllVisible(page); PageSetAllVisible(page);