On Fri, Jun 7, 2024 at 3:06 PM Thomas Munro <thomas.mu...@gmail.com> wrote: > On Fri, Jun 7, 2024 at 3:00 PM Alexander Lakhin <exclus...@gmail.com> wrote: > > My bisect run ended with: > > 210622c60e1a9db2e2730140b8106ab57d259d15 is the first bad commit > > > > Author: Thomas Munro <tmu...@postgresql.org> > > Date: Wed Apr 3 00:03:08 2024 +1300 > > > > Provide vectored variant of ReadBuffer(). > > > > Other buildfarm failures with this Assert I could find kind of confirm this: > > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=calliphoridae&dt=2024-04-03%2003%3A32%3A18 > > (presumably a first failure of this sort) > > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=tamandua&dt=2024-04-04%2015%3A38%3A16 > > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=margay&dt=2024-05-07%2004%3A00%3A08 > > Looking...
What Noah described[1] is what should be happening already, I think, but 210622c6 unconditionally zeroed the page. Oops. The attached seems to cure his repro for me. Does it also cure your test? I couldn't see that variant myself for some reason, but it seems to make sense as the explanation. I would probably adjust the function name or perhaps consider refactoring slightly, but first let's confirm that this is the same issue and fix. [1] https://www.postgresql.org/message-id/flat/20240512171658.7e.nmi...@google.com
From f3bb1d69a57bea820895efaf366371463e62235d Mon Sep 17 00:00:00 2001 From: Thomas Munro <thomas.mu...@gmail.com> Date: Fri, 7 Jun 2024 17:49:19 +1200 Subject: [PATCH] Fix RBM_ZERO_AND_LOCK. Commit 210622c6 accidentally zeroed out pages even if they were found in the buffer pool. It should always lock the page, but it should only zero pages that were not already found as an optimization to avoid I/O. Otherwise, concurrent readers that hold only a pin might see corrupted page contents changing under their feet. Reported-by: Noah Misch <n...@leadboat.com> Reported-by: Alexander Lakhin <exclus...@gmail.com> Discussion: https://postgr.es/m/20240512171658.7e.nmi...@google.com Discussion: https://postgr.es/m/7ed10231-ce47-03d5-d3f9-4aea0dc7d5a4%40gmail.com --- src/backend/storage/buffer/bufmgr.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index 49637284f91..238fc0e3547 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1016,7 +1016,7 @@ ExtendBufferedRelTo(BufferManagerRelation bmr, * return. */ static void -ZeroBuffer(Buffer buffer, ReadBufferMode mode) +ZeroBuffer(Buffer buffer, ReadBufferMode mode, bool zero) { BufferDesc *bufHdr; uint32 buf_state; @@ -1034,7 +1034,8 @@ ZeroBuffer(Buffer buffer, ReadBufferMode mode) LockBufferForCleanup(buffer); } - memset(BufferGetPage(buffer), 0, BLCKSZ); + if (zero) + memset(BufferGetPage(buffer), 0, BLCKSZ); if (BufferIsLocal(buffer)) { @@ -1185,7 +1186,7 @@ ReadBuffer_common(Relation rel, SMgrRelation smgr, char smgr_persistence, buffer = PinBufferForBlock(rel, smgr, smgr_persistence, forkNum, blockNum, strategy, &found); - ZeroBuffer(buffer, mode); + ZeroBuffer(buffer, mode, !found); return buffer; } -- 2.45.1
