From 0e2f3d78bf5ab869da0dbefeba629d74d4078655 Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Thu, 27 Jun 2024 21:06:32 +0300 Subject: Fix MVCC bug with prepared xact with subxacts on standby We did not recover the subtransaction IDs of prepared transactions when starting a hot standby from a shutdown checkpoint. As a result, such subtransactions were considered as aborted, rather than in-progress. That would lead to hint bits being set incorrectly, and the subtransactions suddenly becoming visible to old snapshots when the prepared transaction was committed. To fix, update pg_subtrans with prepared transactions's subxids when starting hot standby from a shutdown checkpoint. The snapshots taken from that state need to be marked as "suboverflowed", so that we also check the pg_subtrans. Backport to all supported versions. Discussion: https://www.postgresql.org/message-id/6b852e98-2d49-4ca1-9e95-db419a2696e0@iki.fi --- src/backend/access/transam/xlog.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) (limited to 'src/backend/access/transam/xlog.c') diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index 7b8e6206459..daad1ff1c3b 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -5273,6 +5273,9 @@ StartupXLOG(void) RunningTransactionsData running; TransactionId latestCompletedXid; + /* Update pg_subtrans entries for any prepared transactions */ + StandbyRecoverPreparedTransactions(); + /* * Construct a RunningTransactions snapshot representing a * shut down server, with only prepared transactions still @@ -5281,7 +5284,7 @@ StartupXLOG(void) */ running.xcnt = nxids; running.subxcnt = 0; - running.subxid_overflow = false; + running.subxid_status = SUBXIDS_IN_SUBTRANS; running.nextXid = XidFromFullTransactionId(checkPoint.nextXid); running.oldestRunningXid = oldestActiveXID; latestCompletedXid = XidFromFullTransactionId(checkPoint.nextXid); @@ -5291,8 +5294,6 @@ StartupXLOG(void) running.xids = xids; ProcArrayApplyRecoveryInfo(&running); - - StandbyRecoverPreparedTransactions(); } } @@ -7647,6 +7648,9 @@ xlog_redo(XLogReaderState *record) oldestActiveXID = PrescanPreparedTransactions(&xids, &nxids); + /* Update pg_subtrans entries for any prepared transactions */ + StandbyRecoverPreparedTransactions(); + /* * Construct a RunningTransactions snapshot representing a shut * down server, with only prepared transactions still alive. We're @@ -7655,7 +7659,7 @@ xlog_redo(XLogReaderState *record) */ running.xcnt = nxids; running.subxcnt = 0; - running.subxid_overflow = false; + running.subxid_status = SUBXIDS_IN_SUBTRANS; running.nextXid = XidFromFullTransactionId(checkPoint.nextXid); running.oldestRunningXid = oldestActiveXID; latestCompletedXid = XidFromFullTransactionId(checkPoint.nextXid); @@ -7665,8 +7669,6 @@ xlog_redo(XLogReaderState *record) running.xids = xids; ProcArrayApplyRecoveryInfo(&running); - - StandbyRecoverPreparedTransactions(); } /* ControlFile->checkPointCopy always tracks the latest ckpt XID */ -- cgit v1.2.3