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Commit7cb7122

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Remove O(N^2) performance issue with multiple SAVEPOINTs.
Subtransaction locks now released en masse at main commit, rather thanrepeatedly re-scanning for locks as we ascend the nested transaction tree.Split transaction state TBLOCK_SUBEND into two states, TBLOCK_SUBCOMMITand TBLOCK_SUBRELEASE to allow the commit path to be optimised usingthe existing code in ResourceOwnerRelease() which appears to have beenintended for this usage, judging from comments therein.
1 parent8e5ac74 commit7cb7122

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1 file changed

+70
-32
lines changed
  • src/backend/access/transam

1 file changed

+70
-32
lines changed

‎src/backend/access/transam/xact.c

Lines changed: 70 additions & 32 deletions
Original file line numberDiff line numberDiff line change
@@ -118,7 +118,8 @@ typedef enum TBlockState
118118
/* subtransaction states */
119119
TBLOCK_SUBBEGIN,/* starting a subtransaction */
120120
TBLOCK_SUBINPROGRESS,/* live subtransaction */
121-
TBLOCK_SUBEND,/* RELEASE received */
121+
TBLOCK_SUBRELEASE,/* RELEASE received */
122+
TBLOCK_SUBCOMMIT,/* COMMIT received while TBLOCK_SUBINPROGRESS */
122123
TBLOCK_SUBABORT,/* failed subxact, awaiting ROLLBACK */
123124
TBLOCK_SUBABORT_END,/* failed subxact, ROLLBACK received */
124125
TBLOCK_SUBABORT_PENDING,/* live subxact, ROLLBACK received */
@@ -272,7 +273,7 @@ static TransactionId RecordTransactionAbort(bool isSubXact);
272273
staticvoidStartTransaction(void);
273274

274275
staticvoidStartSubTransaction(void);
275-
staticvoidCommitSubTransaction(void);
276+
staticvoidCommitSubTransaction(boolisTopLevel);
276277
staticvoidAbortSubTransaction(void);
277278
staticvoidCleanupSubTransaction(void);
278279
staticvoidPushTransaction(void);
@@ -2442,7 +2443,8 @@ StartTransactionCommand(void)
24422443
caseTBLOCK_BEGIN:
24432444
caseTBLOCK_SUBBEGIN:
24442445
caseTBLOCK_END:
2445-
caseTBLOCK_SUBEND:
2446+
caseTBLOCK_SUBRELEASE:
2447+
caseTBLOCK_SUBCOMMIT:
24462448
caseTBLOCK_ABORT_END:
24472449
caseTBLOCK_SUBABORT_END:
24482450
caseTBLOCK_ABORT_PENDING:
@@ -2572,17 +2574,32 @@ CommitTransactionCommand(void)
25722574
break;
25732575

25742576
/*
2575-
* We were issued aCOMMIT orRELEASE command, so we end the
2577+
* We were issued a RELEASE command, so we end the
25762578
* current subtransaction and return to the parent transaction.
2577-
* The parent might be ended too, so repeat till weare all the
2578-
*way out orfind an INPROGRESS transaction.
2579+
* The parent might be ended too, so repeat till wefind an
2580+
*INPROGRESS transaction orsubtransaction.
25792581
*/
2580-
caseTBLOCK_SUBEND:
2582+
caseTBLOCK_SUBRELEASE:
25812583
do
25822584
{
2583-
CommitSubTransaction();
2585+
CommitSubTransaction(false);
25842586
s=CurrentTransactionState;/* changed by pop */
2585-
}while (s->blockState==TBLOCK_SUBEND);
2587+
}while (s->blockState==TBLOCK_SUBRELEASE);
2588+
2589+
Assert(s->blockState==TBLOCK_INPROGRESS||
2590+
s->blockState==TBLOCK_SUBINPROGRESS);
2591+
break;
2592+
2593+
/*
2594+
* We were issued a COMMIT, so we end the current subtransaction
2595+
* hierarchy and perform final commit.
2596+
*/
2597+
caseTBLOCK_SUBCOMMIT:
2598+
do
2599+
{
2600+
CommitSubTransaction(true);
2601+
s=CurrentTransactionState;/* changed by pop */
2602+
}while (s->blockState==TBLOCK_SUBCOMMIT);
25862603
/* If we had a COMMIT command, finish off the main xact too */
25872604
if (s->blockState==TBLOCK_END)
25882605
{
@@ -2597,10 +2614,8 @@ CommitTransactionCommand(void)
25972614
s->blockState=TBLOCK_DEFAULT;
25982615
}
25992616
else
2600-
{
2601-
Assert(s->blockState==TBLOCK_INPROGRESS||
2602-
s->blockState==TBLOCK_SUBINPROGRESS);
2603-
}
2617+
elog(ERROR,"CommitTransactionCommand: unexpected state %s",
2618+
BlockStateAsString(s->blockState));
26042619
break;
26052620

26062621
/*
@@ -2814,7 +2829,8 @@ AbortCurrentTransaction(void)
28142829
* applies if we get a failure while ending a subtransaction.
28152830
*/
28162831
caseTBLOCK_SUBBEGIN:
2817-
caseTBLOCK_SUBEND:
2832+
caseTBLOCK_SUBRELEASE:
2833+
caseTBLOCK_SUBCOMMIT:
28182834
caseTBLOCK_SUBABORT_PENDING:
28192835
caseTBLOCK_SUBRESTART:
28202836
AbortSubTransaction();
@@ -3122,7 +3138,8 @@ BeginTransactionBlock(void)
31223138
caseTBLOCK_BEGIN:
31233139
caseTBLOCK_SUBBEGIN:
31243140
caseTBLOCK_END:
3125-
caseTBLOCK_SUBEND:
3141+
caseTBLOCK_SUBRELEASE:
3142+
caseTBLOCK_SUBCOMMIT:
31263143
caseTBLOCK_ABORT_END:
31273144
caseTBLOCK_SUBABORT_END:
31283145
caseTBLOCK_ABORT_PENDING:
@@ -3232,7 +3249,7 @@ EndTransactionBlock(void)
32323249
while (s->parent!=NULL)
32333250
{
32343251
if (s->blockState==TBLOCK_SUBINPROGRESS)
3235-
s->blockState=TBLOCK_SUBEND;
3252+
s->blockState=TBLOCK_SUBCOMMIT;
32363253
else
32373254
elog(FATAL,"EndTransactionBlock: unexpected state %s",
32383255
BlockStateAsString(s->blockState));
@@ -3290,7 +3307,8 @@ EndTransactionBlock(void)
32903307
caseTBLOCK_BEGIN:
32913308
caseTBLOCK_SUBBEGIN:
32923309
caseTBLOCK_END:
3293-
caseTBLOCK_SUBEND:
3310+
caseTBLOCK_SUBRELEASE:
3311+
caseTBLOCK_SUBCOMMIT:
32943312
caseTBLOCK_ABORT_END:
32953313
caseTBLOCK_SUBABORT_END:
32963314
caseTBLOCK_ABORT_PENDING:
@@ -3382,7 +3400,8 @@ UserAbortTransactionBlock(void)
33823400
caseTBLOCK_BEGIN:
33833401
caseTBLOCK_SUBBEGIN:
33843402
caseTBLOCK_END:
3385-
caseTBLOCK_SUBEND:
3403+
caseTBLOCK_SUBRELEASE:
3404+
caseTBLOCK_SUBCOMMIT:
33863405
caseTBLOCK_ABORT_END:
33873406
caseTBLOCK_SUBABORT_END:
33883407
caseTBLOCK_ABORT_PENDING:
@@ -3427,7 +3446,8 @@ DefineSavepoint(char *name)
34273446
caseTBLOCK_BEGIN:
34283447
caseTBLOCK_SUBBEGIN:
34293448
caseTBLOCK_END:
3430-
caseTBLOCK_SUBEND:
3449+
caseTBLOCK_SUBRELEASE:
3450+
caseTBLOCK_SUBCOMMIT:
34313451
caseTBLOCK_ABORT:
34323452
caseTBLOCK_SUBABORT:
34333453
caseTBLOCK_ABORT_END:
@@ -3483,7 +3503,8 @@ ReleaseSavepoint(List *options)
34833503
caseTBLOCK_BEGIN:
34843504
caseTBLOCK_SUBBEGIN:
34853505
caseTBLOCK_END:
3486-
caseTBLOCK_SUBEND:
3506+
caseTBLOCK_SUBRELEASE:
3507+
caseTBLOCK_SUBCOMMIT:
34873508
caseTBLOCK_ABORT:
34883509
caseTBLOCK_SUBABORT:
34893510
caseTBLOCK_ABORT_END:
@@ -3534,7 +3555,7 @@ ReleaseSavepoint(List *options)
35343555
for (;;)
35353556
{
35363557
Assert(xact->blockState==TBLOCK_SUBINPROGRESS);
3537-
xact->blockState=TBLOCK_SUBEND;
3558+
xact->blockState=TBLOCK_SUBRELEASE;
35383559
if (xact==target)
35393560
break;
35403561
xact=xact->parent;
@@ -3583,7 +3604,8 @@ RollbackToSavepoint(List *options)
35833604
caseTBLOCK_BEGIN:
35843605
caseTBLOCK_SUBBEGIN:
35853606
caseTBLOCK_END:
3586-
caseTBLOCK_SUBEND:
3607+
caseTBLOCK_SUBRELEASE:
3608+
caseTBLOCK_SUBCOMMIT:
35873609
caseTBLOCK_ABORT_END:
35883610
caseTBLOCK_SUBABORT_END:
35893611
caseTBLOCK_ABORT_PENDING:
@@ -3691,7 +3713,8 @@ BeginInternalSubTransaction(char *name)
36913713
caseTBLOCK_DEFAULT:
36923714
caseTBLOCK_BEGIN:
36933715
caseTBLOCK_SUBBEGIN:
3694-
caseTBLOCK_SUBEND:
3716+
caseTBLOCK_SUBRELEASE:
3717+
caseTBLOCK_SUBCOMMIT:
36953718
caseTBLOCK_ABORT:
36963719
caseTBLOCK_SUBABORT:
36973720
caseTBLOCK_ABORT_END:
@@ -3726,7 +3749,7 @@ ReleaseCurrentSubTransaction(void)
37263749
BlockStateAsString(s->blockState));
37273750
Assert(s->state==TRANS_INPROGRESS);
37283751
MemoryContextSwitchTo(CurTransactionContext);
3729-
CommitSubTransaction();
3752+
CommitSubTransaction(false);
37303753
s=CurrentTransactionState;/* changed by pop */
37313754
Assert(s->state==TRANS_INPROGRESS);
37323755
}
@@ -3757,7 +3780,8 @@ RollbackAndReleaseCurrentSubTransaction(void)
37573780
caseTBLOCK_SUBBEGIN:
37583781
caseTBLOCK_INPROGRESS:
37593782
caseTBLOCK_END:
3760-
caseTBLOCK_SUBEND:
3783+
caseTBLOCK_SUBRELEASE:
3784+
caseTBLOCK_SUBCOMMIT:
37613785
caseTBLOCK_ABORT:
37623786
caseTBLOCK_ABORT_END:
37633787
caseTBLOCK_SUBABORT_END:
@@ -3831,7 +3855,8 @@ AbortOutOfAnyTransaction(void)
38313855
*/
38323856
caseTBLOCK_SUBBEGIN:
38333857
caseTBLOCK_SUBINPROGRESS:
3834-
caseTBLOCK_SUBEND:
3858+
caseTBLOCK_SUBRELEASE:
3859+
caseTBLOCK_SUBCOMMIT:
38353860
caseTBLOCK_SUBABORT_PENDING:
38363861
caseTBLOCK_SUBRESTART:
38373862
AbortSubTransaction();
@@ -3903,7 +3928,8 @@ TransactionBlockStatusCode(void)
39033928
caseTBLOCK_INPROGRESS:
39043929
caseTBLOCK_SUBINPROGRESS:
39053930
caseTBLOCK_END:
3906-
caseTBLOCK_SUBEND:
3931+
caseTBLOCK_SUBRELEASE:
3932+
caseTBLOCK_SUBCOMMIT:
39073933
caseTBLOCK_PREPARE:
39083934
return'T';/* in transaction */
39093935
caseTBLOCK_ABORT:
@@ -3987,9 +4013,13 @@ StartSubTransaction(void)
39874013
*
39884014
*The caller has to make sure to always reassign CurrentTransactionState
39894015
*if it has a local pointer to it after calling this function.
4016+
*
4017+
*isTopLevel means that this CommitSubTransaction() is being issued as a
4018+
*sequence of actions leading directly to a main transaction commit
4019+
*allowing some actions to be optimised.
39904020
*/
39914021
staticvoid
3992-
CommitSubTransaction(void)
4022+
CommitSubTransaction(boolisTopLevel)
39934023
{
39944024
TransactionStates=CurrentTransactionState;
39954025

@@ -4036,15 +4066,21 @@ CommitSubTransaction(void)
40364066

40374067
/*
40384068
* The only lock we actually release here is the subtransaction XID lock.
4039-
* The rest just get transferred to the parent resource owner.
40404069
*/
40414070
CurrentResourceOwner=s->curTransactionOwner;
40424071
if (TransactionIdIsValid(s->transactionId))
40434072
XactLockTableDelete(s->transactionId);
40444073

4074+
/*
4075+
* Other locks should get transferred to their parent resource owner.
4076+
* Doing that is an O(N^2) operation, so if isTopLevel then we can just
4077+
* leave the lock records as they are, knowing they will all get released
4078+
* by the top level commit using ProcReleaseLocks(). We only optimize
4079+
* this for commit; aborts may need to do other cleanup.
4080+
*/
40454081
ResourceOwnerRelease(s->curTransactionOwner,
40464082
RESOURCE_RELEASE_LOCKS,
4047-
true,false);
4083+
true,isTopLevel);
40484084
ResourceOwnerRelease(s->curTransactionOwner,
40494085
RESOURCE_RELEASE_AFTER_LOCKS,
40504086
true, false);
@@ -4398,8 +4434,10 @@ BlockStateAsString(TBlockState blockState)
43984434
return"SUB BEGIN";
43994435
caseTBLOCK_SUBINPROGRESS:
44004436
return"SUB INPROGRS";
4401-
caseTBLOCK_SUBEND:
4402-
return"SUB END";
4437+
caseTBLOCK_SUBRELEASE:
4438+
return"SUB RELEASE";
4439+
caseTBLOCK_SUBCOMMIT:
4440+
return"SUB COMMIT";
44034441
caseTBLOCK_SUBABORT:
44044442
return"SUB ABORT";
44054443
caseTBLOCK_SUBABORT_END:

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