From b1f14c9672026a647b826455f03552ca30846e48 Mon Sep 17 00:00:00 2001 From: Tomas Vondra Date: Fri, 13 Mar 2026 22:42:29 +0100 Subject: [PATCH] Use GetXLogInsertEndRecPtr in gistGetFakeLSN The function used GetXLogInsertRecPtr() to generate the fake LSN. Most of the time this is the same as what XLogInsert() would return, and so it works fine with the XLogFlush() call. But if the last record ends at a page boundary, GetXLogInsertRecPtr() returns LSN pointing after the page header. In such case XLogFlush() fails with errors like this: ERROR: xlog flush request 0/01BD2018 is not satisfied --- flushed only to 0/01BD2000 Such failures are very hard to trigger, particularly outside aggressive test scenarios. Fixed by introducing GetXLogInsertEndRecPtr(), returning the correct LSN without skipping the header. This is the same as GetXLogInsertRecPtr(), except that it calls XLogBytePosToEndRecPtr(). Initial investigation by me, root cause identified by Andres Freund. This is a long-standing bug in gistGetFakeLSN(), probably introduced by c6b92041d38 in PG13. Backpatch to all supported versions. Reported-by: Peter Geoghegan Reviewed-by: Andres Freund Reviewed-by: Noah Misch Discussion: https://postgr.es/m/vf4hbwrotvhbgcnknrqmfbqlu75oyjkmausvy66ic7x7vuhafx@e4rvwavtjswo Backpatch-through: 14 --- src/backend/access/gist/gistutil.c | 2 +- src/backend/access/transam/xlog.c | 16 ++++++++++++++++ src/include/access/xlog.h | 1 + 3 files changed, 18 insertions(+), 1 deletion(-) diff --git a/src/backend/access/gist/gistutil.c b/src/backend/access/gist/gistutil.c index 27972fad2b0..e7e4b273e19 100644 --- a/src/backend/access/gist/gistutil.c +++ b/src/backend/access/gist/gistutil.c @@ -1034,7 +1034,7 @@ gistGetFakeLSN(Relation rel) * last call. */ static XLogRecPtr lastlsn = InvalidXLogRecPtr; - XLogRecPtr currlsn = GetXLogInsertRecPtr(); + XLogRecPtr currlsn = GetXLogInsertEndRecPtr(); /* Shouldn't be called for WAL-logging relations */ Assert(!RelationNeedsWAL(rel)); diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index b9b678f3722..f760291e10c 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -9595,6 +9595,22 @@ GetXLogInsertRecPtr(void) return XLogBytePosToRecPtr(current_bytepos); } +/* + * Get latest WAL record end pointer + */ +XLogRecPtr +GetXLogInsertEndRecPtr(void) +{ + XLogCtlInsert *Insert = &XLogCtl->Insert; + uint64 current_bytepos; + + SpinLockAcquire(&Insert->insertpos_lck); + current_bytepos = Insert->CurrBytePos; + SpinLockRelease(&Insert->insertpos_lck); + + return XLogBytePosToEndRecPtr(current_bytepos); +} + /* * Get latest WAL write pointer */ diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h index fdfb572467b..958f39edda4 100644 --- a/src/include/access/xlog.h +++ b/src/include/access/xlog.h @@ -238,6 +238,7 @@ extern bool RecoveryInProgress(void); extern RecoveryState GetRecoveryState(void); extern bool XLogInsertAllowed(void); extern XLogRecPtr GetXLogInsertRecPtr(void); +extern XLogRecPtr GetXLogInsertEndRecPtr(void); extern XLogRecPtr GetXLogWriteRecPtr(void); extern uint64 GetSystemIdentifier(void);