database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-11-03 09:13:20 +03:00
Code Activity

Fix theoretical torn page hazard.

Browse Source 
The original report was concerned with a possible inconsistency
between the heap and the visibility map, which I was unable to
confirm. The concern has been retracted.

However, there did seem to be a torn page hazard when using
checksums. By not setting the heap page LSN during redo, the
protections of minRecoveryPoint were bypassed. Fixed, along with a
misleading comment.

It may have been impossible to hit this problem in practice, because
it would require a page tear between the checksum and the flags, so I
am marking this as a theoretical risk. But, as discussed, it did
violate expectations about the page LSN, so it may have other
consequences.

Backpatch to all supported versions.

Reported-by: Konstantin Knizhnik
Reviewed-by: Konstantin Knizhnik
Discussion: https://postgr.es/m/fed17dac-8cb8-4f5b-d462-1bb4908c029e@garret.ru
Backpatch-through: 11
This commit is contained in:
Jeff Davis
2022-11-10 14:46:30 -08:00
parent 294a2199a3
commit 58a45bb1d8
1 changed files with 4 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
src/backend/access/heap/heapam.c
View File

@@ -7956,8 +7956,7 @@ heap_xlog_visible(XLogReaderState *record)
/* /*
* We don't bump the LSN of the heap page when setting the visibility * We don't bump the LSN of the heap page when setting the visibility
* map bit (unless checksums or wal_hint_bits is enabled, in which * map bit (unless checksums or wal_hint_bits is enabled, in which
* case we must), because that would generate an unworkable volume of * case we must). This exposes us to torn page hazards, but since
* full-page writes. This exposes us to torn page hazards, but since
* we're not inspecting the existing page contents in any way, we * we're not inspecting the existing page contents in any way, we
* don't care. * don't care.
* *
@@ -7971,6 +7970,9 @@ heap_xlog_visible(XLogReaderState *record)
PageSetAllVisible(page); PageSetAllVisible(page);
if (XLogHintBitIsNeeded())
PageSetLSN(page, lsn);
MarkBufferDirty(buffer); MarkBufferDirty(buffer);
} }
else if (action == BLK_RESTORED) else if (action == BLK_RESTORED)