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Commit5c11725

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Rearrange storage of data in xl_running_xacts.
Previously we stored all xids mixed together.Now we store top-level xids first, followedby all subxids. Also skip logging any subxidsif the snapshot is suboverflowed, since thereare potentially large numbers of them and theyare not useful in that case anyway. Has valuein the envisaged design for decoding of WAL.No planned effect on Hot Standby.Andres Freund, reviewed by me
1 parentc111306 commit5c11725

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4 files changed

+52
-25
lines changed

4 files changed

+52
-25
lines changed

‎src/backend/access/transam/xlog.c‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -5631,6 +5631,7 @@ StartupXLOG(void)
56315631
* subxids are listed with their parent prepared transactions.
56325632
*/
56335633
running.xcnt=nxids;
5634+
running.subxcnt=0;
56345635
running.subxid_overflow= false;
56355636
running.nextXid=checkPoint.nextXid;
56365637
running.oldestRunningXid=oldestActiveXID;
@@ -7834,6 +7835,7 @@ xlog_redo(XLogRecPtr lsn, XLogRecord *record)
78347835
* with their parent prepared transactions.
78357836
*/
78367837
running.xcnt=nxids;
7838+
running.subxcnt=0;
78377839
running.subxid_overflow= false;
78387840
running.nextXid=checkPoint.nextXid;
78397841
running.oldestRunningXid=oldestActiveXID;

‎src/backend/storage/ipc/procarray.c‎

Lines changed: 43 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -501,6 +501,13 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
501501
* Remove stale transactions, if any.
502502
*/
503503
ExpireOldKnownAssignedTransactionIds(running->oldestRunningXid);
504+
505+
/*
506+
* Remove stale locks, if any.
507+
*
508+
* Locks are always assigned to the toplevel xid so we don't need to care
509+
* about subxcnt/subxids (and by extension not about ->suboverflowed).
510+
*/
504511
StandbyReleaseOldLocks(running->xcnt,running->xids);
505512

506513
/*
@@ -581,13 +588,13 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
581588
* Allocate a temporary array to avoid modifying the array passed as
582589
* argument.
583590
*/
584-
xids=palloc(sizeof(TransactionId)*running->xcnt);
591+
xids=palloc(sizeof(TransactionId)*(running->xcnt+running->subxcnt));
585592

586593
/*
587594
* Add to the temp array any xids which have not already completed.
588595
*/
589596
nxids=0;
590-
for (i=0;i<running->xcnt;i++)
597+
for (i=0;i<running->xcnt+running->subxcnt;i++)
591598
{
592599
TransactionIdxid=running->xids[i];
593600

@@ -1627,15 +1634,13 @@ GetRunningTransactionData(void)
16271634
oldestRunningXid=ShmemVariableCache->nextXid;
16281635

16291636
/*
1630-
* Spin over procArray collecting all xids and subxids.
1637+
* Spin over procArray collecting all xids
16311638
*/
16321639
for (index=0;index<arrayP->numProcs;index++)
16331640
{
16341641
intpgprocno=arrayP->pgprocnos[index];
1635-
volatilePGPROC*proc=&allProcs[pgprocno];
16361642
volatilePGXACT*pgxact=&allPgXact[pgprocno];
16371643
TransactionIdxid;
1638-
intnxids;
16391644

16401645
/* Fetch xid just once - see GetNewTransactionId */
16411646
xid=pgxact->xid;
@@ -1652,30 +1657,46 @@ GetRunningTransactionData(void)
16521657
if (TransactionIdPrecedes(xid,oldestRunningXid))
16531658
oldestRunningXid=xid;
16541659

1655-
/*
1656-
* Save subtransaction XIDs. Other backends can't add or remove
1657-
* entries while we're holding XidGenLock.
1658-
*/
1659-
nxids=pgxact->nxids;
1660-
if (nxids>0)
1661-
{
1662-
memcpy(&xids[count], (void*)proc->subxids.xids,
1663-
nxids*sizeof(TransactionId));
1664-
count+=nxids;
1665-
subcount+=nxids;
1660+
if (pgxact->overflowed)
1661+
suboverflowed= true;
1662+
}
16661663

1667-
if (pgxact->overflowed)
1668-
suboverflowed= true;
1664+
/*
1665+
* Spin over procArray collecting all subxids, but only if there hasn't
1666+
* been a suboverflow.
1667+
*/
1668+
if (!suboverflowed)
1669+
{
1670+
for (index=0;index<arrayP->numProcs;index++)
1671+
{
1672+
intpgprocno=arrayP->pgprocnos[index];
1673+
volatilePGPROC*proc=&allProcs[pgprocno];
1674+
volatilePGXACT*pgxact=&allPgXact[pgprocno];
1675+
intnxids;
16691676

16701677
/*
1671-
* Top-level XID of a transaction is always less than any of its
1672-
* subxids, so we don't need to check if any of the subxids are
1673-
* smaller than oldestRunningXid
1678+
* Save subtransaction XIDs. Other backends can't add or remove
1679+
* entries while we're holding XidGenLock.
16741680
*/
1681+
nxids=pgxact->nxids;
1682+
if (nxids>0)
1683+
{
1684+
memcpy(&xids[count], (void*)proc->subxids.xids,
1685+
nxids*sizeof(TransactionId));
1686+
count+=nxids;
1687+
subcount+=nxids;
1688+
1689+
/*
1690+
* Top-level XID of a transaction is always less than any of
1691+
* its subxids, so we don't need to check if any of the subxids
1692+
* are smaller than oldestRunningXid
1693+
*/
1694+
}
16751695
}
16761696
}
16771697

1678-
CurrentRunningXacts->xcnt=count;
1698+
CurrentRunningXacts->xcnt=count-subcount;
1699+
CurrentRunningXacts->subxcnt=subcount;
16791700
CurrentRunningXacts->subxid_overflow=suboverflowed;
16801701
CurrentRunningXacts->nextXid=ShmemVariableCache->nextXid;
16811702
CurrentRunningXacts->oldestRunningXid=oldestRunningXid;

‎src/backend/storage/ipc/standby.c‎

Lines changed: 5 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -778,6 +778,7 @@ standby_redo(XLogRecPtr lsn, XLogRecord *record)
778778
RunningTransactionsDatarunning;
779779

780780
running.xcnt=xlrec->xcnt;
781+
running.subxcnt=xlrec->subxcnt;
781782
running.subxid_overflow=xlrec->subxid_overflow;
782783
running.nextXid=xlrec->nextXid;
783784
running.latestCompletedXid=xlrec->latestCompletedXid;
@@ -897,6 +898,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
897898
XLogRecPtrrecptr;
898899

899900
xlrec.xcnt=CurrRunningXacts->xcnt;
901+
xlrec.subxcnt=CurrRunningXacts->subxcnt;
900902
xlrec.subxid_overflow=CurrRunningXacts->subxid_overflow;
901903
xlrec.nextXid=CurrRunningXacts->nextXid;
902904
xlrec.oldestRunningXid=CurrRunningXacts->oldestRunningXid;
@@ -912,7 +914,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
912914
{
913915
rdata[0].next=&(rdata[1]);
914916
rdata[1].data= (char*)CurrRunningXacts->xids;
915-
rdata[1].len=xlrec.xcnt*sizeof(TransactionId);
917+
rdata[1].len=(xlrec.xcnt+xlrec.subxcnt)*sizeof(TransactionId);
916918
rdata[1].buffer=InvalidBuffer;
917919
lastrdata=1;
918920
}
@@ -931,8 +933,8 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
931933
CurrRunningXacts->nextXid);
932934
else
933935
elog(trace_recovery(DEBUG2),
934-
"snapshot of %u running transaction ids (lsn %X/%X oldest xid %u latest complete %u next xid %u)",
935-
CurrRunningXacts->xcnt,
936+
"snapshot of %u+%u running transaction ids (lsn %X/%X oldest xid %u latest complete %u next xid %u)",
937+
CurrRunningXacts->xcnt,CurrRunningXacts->subxcnt,
936938
(uint32) (recptr >>32), (uint32)recptr,
937939
CurrRunningXacts->oldestRunningXid,
938940
CurrRunningXacts->latestCompletedXid,

‎src/include/storage/standby.h‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -68,6 +68,7 @@ typedef struct xl_standby_locks
6868
typedefstructxl_running_xacts
6969
{
7070
intxcnt;/* # of xact ids in xids[] */
71+
intsubxcnt;/* # of subxact ids in xids[] */
7172
boolsubxid_overflow;/* snapshot overflowed, subxids missing */
7273
TransactionIdnextXid;/* copy of ShmemVariableCache->nextXid */
7374
TransactionIdoldestRunningXid;/* *not* oldestXmin */
@@ -98,6 +99,7 @@ extern void standby_desc(StringInfo buf, uint8 xl_info, char *rec);
9899
typedefstructRunningTransactionsData
99100
{
100101
intxcnt;/* # of xact ids in xids[] */
102+
intsubxcnt;/* # of subxact ids in xids[] */
101103
boolsubxid_overflow;/* snapshot overflowed, subxids missing */
102104
TransactionIdnextXid;/* copy of ShmemVariableCache->nextXid */
103105
TransactionIdoldestRunningXid;/* *not* oldestXmin */

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