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Commitd2ee542

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Fix recovery of 2PC transaction during crash recovery
A crash in the middle of a checkpoint with some two-phase state dataalready flushed to disk by this checkpoint could cause a follow-up crashrecovery to recover twice the same transaction, once from what has beenfound in pg_twophase/ at the beginning of recovery and a second timewhen replaying its corresponding record.This would lead to FATAL failures in the startup process duringrecovery, where the same transaction would have a state recovered twiceinstead of once:LOG: recovering prepared transaction 731 from shared memoryLOG: recovering prepared transaction 731 from shared memoryFATAL: lock ExclusiveLock on object 731/0/0 is already heldThis issue is fixed by skipping the addition of any 2PC state comingfrom a record whose equivalent 2PC state file has already been loaded inTwoPhaseState at the beginning of recovery by restoreTwoPhaseData(),which is OK as long as the system has not reached a consistent state.The timing to get a messed up recovery processing is very racy, andwould very unlikely happen. The thread that has reported the issue hasdemonstrated the bug using injection points to force a PANIC in themiddle of a checkpoint.Issue introduced in728bd99, so backpatch all the way down.Reported-by: "suyu.cmj" <mengjuan.cmj@alibaba-inc.com>Author: "suyu.cmj" <mengjuan.cmj@alibaba-inc.com>Author: Michael PaquierDiscussion:https://postgr.es/m/109e6994-b971-48cb-84f6-829646f18b4c.mengjuan.cmj@alibaba-inc.comBackpatch-through: 11
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‎src/backend/access/transam/twophase.c

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Original file line numberDiff line numberDiff line change
@@ -2494,6 +2494,39 @@ PrepareRedoAdd(char *buf, XLogRecPtr start_lsn,
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* that it got added in the redo phase
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*/
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/*
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* In the event of a crash while a checkpoint was running, it may be
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* possible that some two-phase data found its way to disk while its
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* corresponding record needs to be replayed in the follow-up recovery.
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* As the 2PC data was on disk, it has already been restored at the
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* beginning of recovery with restoreTwoPhaseData(), so skip this record
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* to avoid duplicates in TwoPhaseState. If a consistent state has been
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* reached, the record is added to TwoPhaseState and it should have no
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* corresponding file in pg_twophase.
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*/
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if (!XLogRecPtrIsInvalid(start_lsn))
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{
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charpath[MAXPGPATH];
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TwoPhaseFilePath(path,hdr->xid);
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if (access(path,F_OK)==0)
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{
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ereport(reachedConsistency ?ERROR :WARNING,
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(errmsg("could not recover two-phase state file for transaction %u",
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hdr->xid),
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errdetail("Two-phase state file has been found in WAL record %X/%X, but this transaction has already been restored from disk.",
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(uint32) (start_lsn >>32),
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(uint32)start_lsn)));
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return;
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}
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if (errno!=ENOENT)
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ereport(ERROR,
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(errcode_for_file_access(),
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errmsg("could not access file \"%s\": %m",path)));
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}
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/* Get a free gxact from the freelist */
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if (TwoPhaseState->freeGXacts==NULL)
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ereport(ERROR,

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