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Fix MVCC bug with prepared xact with subxacts on standby

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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
This commit is contained in:
Heikki Linnakangas
2024-06-27 21:06:32 +03:00
parent 8b6a7723b5
commit 0e2f3d78bf
7 changed files with 85 additions and 17 deletions
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7
src/backend/access/transam/twophase.c
View File

@@ -2013,9 +2013,8 @@ PrescanPreparedTransactions(TransactionId **xids_p, int *nxids_p)
* This is never called at the end of recovery - we use
* RecoverPreparedTransactions() at that point.
*
* The lack of calls to SubTransSetParent() calls here is by design;
* those calls are made by RecoverPreparedTransactions() at the end of recovery
* for those xacts that need this.
* This updates pg_subtrans, so that any subtransactions will be correctly
* seen as in-progress in snapshots taken during recovery.
*/
void
StandbyRecoverPreparedTransactions(void)
@@ -2035,7 +2034,7 @@ StandbyRecoverPreparedTransactions(void)
buf = ProcessTwoPhaseBuffer(xid,
gxact->prepare_start_lsn,
gxact->ondisk, false, false);
gxact->ondisk, true, false);
if (buf != NULL)
pfree(buf);
}

14
src/backend/access/transam/xlog.c
View File

@@ -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 */