From 578a7fe7b6f8484f6d7caa2fda288abb3fe87aa0 Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Sat, 21 Dec 2024 23:42:39 +0200 Subject: [PATCH] Update TransactionXmin when MyProc->xmin is updated GetSnapshotData() set TransactionXmin = MyProc->xmin, but when SnapshotResetXmin() advanced MyProc->xmin, it did not advance TransactionXmin correspondingly. That meant that TransactionXmin could be older than MyProc->xmin, and XIDs between than TransactionXmin and the real MyProc->xmin could be vacuumed away. One known consequence is in pg_subtrans lookups: we might try to look up the status of an XID that was already truncated away. Back-patch to all supported versions. Reviewed-by: Andres Freund Discussion: https://www.postgresql.org/message-id/d27a046d-a1e4-47d1-a95c-fbabe41debb4@iki.fi --- src/backend/utils/time/snapmgr.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c index e60360338d..e002d0c136 100644 --- a/src/backend/utils/time/snapmgr.c +++ b/src/backend/utils/time/snapmgr.c @@ -875,7 +875,7 @@ SnapshotResetXmin(void) if (pairingheap_is_empty(&RegisteredSnapshots)) { - MyProc->xmin = InvalidTransactionId; + MyProc->xmin = TransactionXmin = InvalidTransactionId; return; } @@ -883,7 +883,7 @@ SnapshotResetXmin(void) pairingheap_first(&RegisteredSnapshots)); if (TransactionIdPrecedes(MyProc->xmin, minSnapshot->xmin)) - MyProc->xmin = minSnapshot->xmin; + MyProc->xmin = TransactionXmin = minSnapshot->xmin; } /* -- 2.39.5