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Commitfefd9a3

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committed
Turn tail recursion into iteration in CommitTransactionCommand()
Usually the compiler will optimize away the tail recursion anyway, butif it doesn't, you can drive the function into stack overflow. Forexample: (n=1000000; printf "BEGIN;"; for ((i=1;i<=$n;i++)); do printf "SAVEPOINT s$i;"; done; printf "ERROR; COMMIT;") | psql >/dev/nullIn order to get better readability and less changes to the existing code therecursion-replacing loop is implemented as a wrapper function.Report by Egor Chindyaskin and Alexander Lakhin.Discussion:https://postgr.es/m/1672760457.940462079%40f306.i.mail.ruAuthor: Alexander Korotkov, Heikki Linnakangas
1 parent6d9751f commitfefd9a3

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1 file changed

+106
-45
lines changed
  • src/backend/access/transam

1 file changed

+106
-45
lines changed

‎src/backend/access/transam/xact.c

Lines changed: 106 additions & 45 deletions
Original file line numberDiff line numberDiff line change
@@ -341,6 +341,9 @@ static void CommitTransaction(void);
341341
staticTransactionIdRecordTransactionAbort(boolisSubXact);
342342
staticvoidStartTransaction(void);
343343

344+
staticvoidCommitTransactionCommandInternal(void);
345+
staticvoidAbortCurrentTransactionInternal(void);
346+
344347
staticvoidStartSubTransaction(void);
345348
staticvoidCommitSubTransaction(void);
346349
staticvoidAbortSubTransaction(void);
@@ -3041,16 +3044,58 @@ RestoreTransactionCharacteristics(const SavedTransactionCharacteristics *s)
30413044
XactDeferrable=s->save_XactDeferrable;
30423045
}
30433046

3044-
30453047
/*
3046-
*CommitTransactionCommand
3048+
*CommitTransactionCommand -- a wrapper function handling the
3049+
*loop over subtransactions to avoid a potentially dangerous recursion
3050+
*in CommitTransactionCommandInternal().
30473051
*/
30483052
void
30493053
CommitTransactionCommand(void)
3054+
{
3055+
while (true)
3056+
{
3057+
switch (CurrentTransactionState->blockState)
3058+
{
3059+
/*
3060+
* The current already-failed subtransaction is ending due to
3061+
* a ROLLBACK or ROLLBACK TO command, so pop it and
3062+
* recursively examine the parent (which could be in any of
3063+
* several states).
3064+
*/
3065+
caseTBLOCK_SUBABORT_END:
3066+
CleanupSubTransaction();
3067+
continue;
3068+
3069+
/*
3070+
* As above, but it's not dead yet, so abort first.
3071+
*/
3072+
caseTBLOCK_SUBABORT_PENDING:
3073+
AbortSubTransaction();
3074+
CleanupSubTransaction();
3075+
continue;
3076+
default:
3077+
break;
3078+
}
3079+
CommitTransactionCommandInternal();
3080+
break;
3081+
}
3082+
}
3083+
3084+
/*
3085+
*CommitTransactionCommandInternal - a function doing all the material work
3086+
*regarding handling the commit transaction command except for loop over
3087+
*subtransactions.
3088+
*/
3089+
staticvoid
3090+
CommitTransactionCommandInternal(void)
30503091
{
30513092
TransactionStates=CurrentTransactionState;
30523093
SavedTransactionCharacteristicssavetc;
30533094

3095+
/* This states are handled in CommitTransactionCommand() */
3096+
Assert(s->blockState!=TBLOCK_SUBABORT_END&&
3097+
s->blockState!=TBLOCK_SUBABORT_PENDING);
3098+
30543099
/* Must save in case we need to restore below */
30553100
SaveTransactionCharacteristics(&savetc);
30563101

@@ -3234,25 +3279,6 @@ CommitTransactionCommand(void)
32343279
BlockStateAsString(s->blockState));
32353280
break;
32363281

3237-
/*
3238-
* The current already-failed subtransaction is ending due to a
3239-
* ROLLBACK or ROLLBACK TO command, so pop it and recursively
3240-
* examine the parent (which could be in any of several states).
3241-
*/
3242-
caseTBLOCK_SUBABORT_END:
3243-
CleanupSubTransaction();
3244-
CommitTransactionCommand();
3245-
break;
3246-
3247-
/*
3248-
* As above, but it's not dead yet, so abort first.
3249-
*/
3250-
caseTBLOCK_SUBABORT_PENDING:
3251-
AbortSubTransaction();
3252-
CleanupSubTransaction();
3253-
CommitTransactionCommand();
3254-
break;
3255-
32563282
/*
32573283
* The current subtransaction is the target of a ROLLBACK TO
32583284
* command. Abort and pop it, then start a new subtransaction
@@ -3310,17 +3336,73 @@ CommitTransactionCommand(void)
33103336
s->blockState=TBLOCK_SUBINPROGRESS;
33113337
}
33123338
break;
3339+
default:
3340+
/* Keep compiler quiet */
3341+
break;
33133342
}
33143343
}
33153344

33163345
/*
3317-
*AbortCurrentTransaction
3346+
*AbortCurrentTransaction -- a wrapper function handling the
3347+
*loop over subtransactions to avoid potentially dangerous recursion in
3348+
*AbortCurrentTransactionInternal().
33183349
*/
33193350
void
33203351
AbortCurrentTransaction(void)
3352+
{
3353+
while (true)
3354+
{
3355+
switch (CurrentTransactionState->blockState)
3356+
{
3357+
/*
3358+
* If we failed while trying to create a subtransaction, clean
3359+
* up the broken subtransaction and abort the parent. The
3360+
* same applies if we get a failure while ending a
3361+
* subtransaction.
3362+
*/
3363+
caseTBLOCK_SUBBEGIN:
3364+
caseTBLOCK_SUBRELEASE:
3365+
caseTBLOCK_SUBCOMMIT:
3366+
caseTBLOCK_SUBABORT_PENDING:
3367+
caseTBLOCK_SUBRESTART:
3368+
AbortSubTransaction();
3369+
CleanupSubTransaction();
3370+
continue;
3371+
3372+
/*
3373+
* Same as above, except the Abort() was already done.
3374+
*/
3375+
caseTBLOCK_SUBABORT_END:
3376+
caseTBLOCK_SUBABORT_RESTART:
3377+
CleanupSubTransaction();
3378+
continue;
3379+
default:
3380+
break;
3381+
}
3382+
AbortCurrentTransactionInternal();
3383+
break;
3384+
}
3385+
}
3386+
3387+
/*
3388+
*AbortCurrentTransactionInternal - a function doing all the material work
3389+
*regarding handling the abort transaction command except for loop over
3390+
*subtransactions.
3391+
*/
3392+
staticvoid
3393+
AbortCurrentTransactionInternal(void)
33213394
{
33223395
TransactionStates=CurrentTransactionState;
33233396

3397+
/* This states are handled in AbortCurrentTransaction() */
3398+
Assert(s->blockState!=TBLOCK_SUBBEGIN&&
3399+
s->blockState!=TBLOCK_SUBRELEASE&&
3400+
s->blockState!=TBLOCK_SUBCOMMIT&&
3401+
s->blockState!=TBLOCK_SUBABORT_PENDING&&
3402+
s->blockState!=TBLOCK_SUBRESTART&&
3403+
s->blockState!=TBLOCK_SUBABORT_END&&
3404+
s->blockState!=TBLOCK_SUBABORT_RESTART);
3405+
33243406
switch (s->blockState)
33253407
{
33263408
caseTBLOCK_DEFAULT:
@@ -3441,29 +3523,8 @@ AbortCurrentTransaction(void)
34413523
AbortSubTransaction();
34423524
s->blockState=TBLOCK_SUBABORT;
34433525
break;
3444-
3445-
/*
3446-
* If we failed while trying to create a subtransaction, clean up
3447-
* the broken subtransaction and abort the parent. The same
3448-
* applies if we get a failure while ending a subtransaction.
3449-
*/
3450-
caseTBLOCK_SUBBEGIN:
3451-
caseTBLOCK_SUBRELEASE:
3452-
caseTBLOCK_SUBCOMMIT:
3453-
caseTBLOCK_SUBABORT_PENDING:
3454-
caseTBLOCK_SUBRESTART:
3455-
AbortSubTransaction();
3456-
CleanupSubTransaction();
3457-
AbortCurrentTransaction();
3458-
break;
3459-
3460-
/*
3461-
* Same as above, except the Abort() was already done.
3462-
*/
3463-
caseTBLOCK_SUBABORT_END:
3464-
caseTBLOCK_SUBABORT_RESTART:
3465-
CleanupSubTransaction();
3466-
AbortCurrentTransaction();
3526+
default:
3527+
/* Keep compiler quiet */
34673528
break;
34683529
}
34693530
}

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