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Commit9c54cfb

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Fix CLOG truncation code to not do the Wrong Thing when there are already
wrapped-around databases. The unvacuumed databases might be fine, orthey might not, but things will definitely not be fine if we remove thewrong CLOG segments. Per trouble report from Gary Wolfe, 1-Apr-2002.
1 parent688781d commit9c54cfb

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+45
-13
lines changed

1 file changed

+45
-13
lines changed

‎src/backend/commands/vacuum.c

Lines changed: 45 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -13,7 +13,7 @@
1313
*
1414
*
1515
* IDENTIFICATION
16-
* $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.221 2002/04/0201:03:05 tgl Exp $
16+
* $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.222 2002/04/0205:11:55 tgl Exp $
1717
*
1818
*-------------------------------------------------------------------------
1919
*/
@@ -557,10 +557,15 @@ vac_update_dbstats(Oid dbid,
557557
staticvoid
558558
vac_truncate_clog(TransactionIdvacuumXID,TransactionIdfrozenXID)
559559
{
560+
TransactionIdmyXID;
560561
Relationrelation;
561562
HeapScanDescscan;
562563
HeapTupletuple;
563564
int32age;
565+
boolvacuumAlreadyWrapped= false;
566+
boolfrozenAlreadyWrapped= false;
567+
568+
myXID=GetCurrentTransactionId();
564569

565570
relation=heap_openr(DatabaseRelationName,AccessShareLock);
566571

@@ -575,28 +580,55 @@ vac_truncate_clog(TransactionId vacuumXID, TransactionId frozenXID)
575580
if (!dbform->datallowconn)
576581
continue;
577582

578-
if (TransactionIdIsNormal(dbform->datvacuumxid)&&
579-
TransactionIdPrecedes(dbform->datvacuumxid,vacuumXID))
580-
vacuumXID=dbform->datvacuumxid;
581-
if (TransactionIdIsNormal(dbform->datfrozenxid)&&
582-
TransactionIdPrecedes(dbform->datfrozenxid,frozenXID))
583-
frozenXID=dbform->datfrozenxid;
583+
if (TransactionIdIsNormal(dbform->datvacuumxid))
584+
{
585+
if (TransactionIdPrecedes(myXID,dbform->datvacuumxid))
586+
vacuumAlreadyWrapped= true;
587+
elseif (TransactionIdPrecedes(dbform->datvacuumxid,vacuumXID))
588+
vacuumXID=dbform->datvacuumxid;
589+
}
590+
if (TransactionIdIsNormal(dbform->datfrozenxid))
591+
{
592+
if (TransactionIdPrecedes(myXID,dbform->datfrozenxid))
593+
frozenAlreadyWrapped= true;
594+
elseif (TransactionIdPrecedes(dbform->datfrozenxid,frozenXID))
595+
frozenXID=dbform->datfrozenxid;
596+
}
584597
}
585598

586599
heap_endscan(scan);
587600

588601
heap_close(relation,AccessShareLock);
589602

603+
/*
604+
* Do not truncate CLOG if we seem to have suffered wraparound already;
605+
* the computed minimum XID might be bogus.
606+
*/
607+
if (vacuumAlreadyWrapped)
608+
{
609+
elog(WARNING,"Some databases have not been vacuumed in over 2 billion transactions."
610+
"\n\tYou may have already suffered transaction-wraparound data loss.");
611+
return;
612+
}
613+
590614
/* Truncate CLOG to the oldest vacuumxid */
591615
TruncateCLOG(vacuumXID);
592616

593617
/* Give warning about impending wraparound problems */
594-
age= (int32) (GetCurrentTransactionId()-frozenXID);
595-
if (age> (int32) ((MaxTransactionId >>3)*3))
596-
elog(WARNING,"Some databases have not been vacuumed in %d transactions."
597-
"\n\tBetter vacuum them within %d transactions,"
598-
"\n\tor you may have a wraparound failure.",
599-
age, (int32) (MaxTransactionId >>1)-age);
618+
if (frozenAlreadyWrapped)
619+
{
620+
elog(WARNING,"Some databases have not been vacuumed in over 1 billion transactions."
621+
"\n\tBetter vacuum them soon, or you may have a wraparound failure.");
622+
}
623+
else
624+
{
625+
age= (int32) (myXID-frozenXID);
626+
if (age> (int32) ((MaxTransactionId >>3)*3))
627+
elog(WARNING,"Some databases have not been vacuumed in %d transactions."
628+
"\n\tBetter vacuum them within %d transactions,"
629+
"\n\tor you may have a wraparound failure.",
630+
age, (int32) (MaxTransactionId >>1)-age);
631+
}
600632
}
601633

602634

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