From 7bf713dd2d0739fbcd4103971ed69c17ebe677ea Mon Sep 17 00:00:00 2001 From: Jeff Davis Date: Thu, 10 Nov 2022 14:46:30 -0800 Subject: [PATCH] Fix theoretical torn page hazard. 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 The concern has been retracted.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 --- src/backend/access/heap/heapam.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c index 23c4b4f901..c74fbd0104 100644 --- a/src/backend/access/heap/heapam.c +++ b/src/backend/access/heap/heapam.c @@ -8823,8 +8823,7 @@ heap_xlog_visible(XLogReaderState *record) /* * 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 - * case we must), because that would generate an unworkable volume of - * full-page writes. This exposes us to torn page hazards, but since + * case we must). This exposes us to torn page hazards, but since * we're not inspecting the existing page contents in any way, we * don't care. * @@ -8838,6 +8837,9 @@ heap_xlog_visible(XLogReaderState *record) PageSetAllVisible(page); + if (XLogHintBitIsNeeded()) + PageSetLSN(page, lsn); + MarkBufferDirty(buffer); } else if (action == BLK_RESTORED)