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Turn tail recursion into iteration in CommitTransactionCommand()

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Usually the compiler will optimize away the tail recursion anyway, but
if it doesn't, you can drive the function into stack overflow. For
example:

    (n=1000000; printf "BEGIN;"; for ((i=1;i<=$n;i++)); do printf "SAVEPOINT s$i;"; done; printf "ERROR; COMMIT;") | psql >/dev/null

In order to get better readability and less changes to the existing code the
recursion-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.ru
Author: Alexander Korotkov, Heikki Linnakangas
pull/159/head
Alexander Korotkov 2 years ago
parent 6d9751fa8f
commit fefd9a3fed
1 changed files with 106 additions and 45 deletions
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
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  1. 151
      src/backend/access/transam/xact.c

151
src/backend/access/transam/xact.c
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@ -341,6 +341,9 @@ static void CommitTransaction(void);
static TransactionId RecordTransactionAbort(bool isSubXact);
static void StartTransaction(void);
static void CommitTransactionCommandInternal(void);
static void AbortCurrentTransactionInternal(void);
static void StartSubTransaction(void);
static void CommitSubTransaction(void);
static void AbortSubTransaction(void);
@ -3041,16 +3044,58 @@ RestoreTransactionCharacteristics(const SavedTransactionCharacteristics *s)
XactDeferrable = s->save_XactDeferrable;
}
/*
* CommitTransactionCommand
* CommitTransactionCommand -- a wrapper function handling the
* loop over subtransactions to avoid a potentially dangerous recursion
* in CommitTransactionCommandInternal().
*/
void
CommitTransactionCommand(void)
{
while (true)
{
switch (CurrentTransactionState->blockState)
{
/*
* The current already-failed subtransaction is ending due to
* a ROLLBACK or ROLLBACK TO command, so pop it and
* recursively examine the parent (which could be in any of
* several states).
*/
case TBLOCK_SUBABORT_END:
CleanupSubTransaction();
continue;
/*
* As above, but it's not dead yet, so abort first.
*/
case TBLOCK_SUBABORT_PENDING:
AbortSubTransaction();
CleanupSubTransaction();
continue;
default:
break;
}
CommitTransactionCommandInternal();
break;
}
}
/*
* CommitTransactionCommandInternal - a function doing all the material work
* regarding handling the commit transaction command except for loop over
* subtransactions.
*/
static void
CommitTransactionCommandInternal(void)
{
TransactionState s = CurrentTransactionState;
SavedTransactionCharacteristics savetc;
/* This states are handled in CommitTransactionCommand() */
Assert(s->blockState != TBLOCK_SUBABORT_END &&
s->blockState != TBLOCK_SUBABORT_PENDING);
/* Must save in case we need to restore below */
SaveTransactionCharacteristics(&savetc);
@ -3234,25 +3279,6 @@ CommitTransactionCommand(void)
BlockStateAsString(s->blockState));
break;
/*
* The current already-failed subtransaction is ending due to a
* ROLLBACK or ROLLBACK TO command, so pop it and recursively
* examine the parent (which could be in any of several states).
*/
case TBLOCK_SUBABORT_END:
CleanupSubTransaction();
CommitTransactionCommand();
break;
/*
* As above, but it's not dead yet, so abort first.
*/
case TBLOCK_SUBABORT_PENDING:
AbortSubTransaction();
CleanupSubTransaction();
CommitTransactionCommand();
break;
/*
* The current subtransaction is the target of a ROLLBACK TO
* command. Abort and pop it, then start a new subtransaction
@ -3310,17 +3336,73 @@ CommitTransactionCommand(void)
s->blockState = TBLOCK_SUBINPROGRESS;
}
break;
default:
/* Keep compiler quiet */
break;
}
}
/*
* AbortCurrentTransaction
* AbortCurrentTransaction -- a wrapper function handling the
* loop over subtransactions to avoid potentially dangerous recursion in
* AbortCurrentTransactionInternal().
*/
void
AbortCurrentTransaction(void)
{
while (true)
{
switch (CurrentTransactionState->blockState)
{
/*
* If we failed while trying to create a subtransaction, clean
* up the broken subtransaction and abort the parent. The
* same applies if we get a failure while ending a
* subtransaction.
*/
case TBLOCK_SUBBEGIN:
case TBLOCK_SUBRELEASE:
case TBLOCK_SUBCOMMIT:
case TBLOCK_SUBABORT_PENDING:
case TBLOCK_SUBRESTART:
AbortSubTransaction();
CleanupSubTransaction();
continue;
/*
* Same as above, except the Abort() was already done.
*/
case TBLOCK_SUBABORT_END:
case TBLOCK_SUBABORT_RESTART:
CleanupSubTransaction();
continue;
default:
break;
}
AbortCurrentTransactionInternal();
break;
}
}
/*
* AbortCurrentTransactionInternal - a function doing all the material work
* regarding handling the abort transaction command except for loop over
* subtransactions.
*/
static void
AbortCurrentTransactionInternal(void)
{
TransactionState s = CurrentTransactionState;
/* This states are handled in AbortCurrentTransaction() */
Assert(s->blockState != TBLOCK_SUBBEGIN &&
s->blockState != TBLOCK_SUBRELEASE &&
s->blockState != TBLOCK_SUBCOMMIT &&
s->blockState != TBLOCK_SUBABORT_PENDING &&
s->blockState != TBLOCK_SUBRESTART &&
s->blockState != TBLOCK_SUBABORT_END &&
s->blockState != TBLOCK_SUBABORT_RESTART);
switch (s->blockState)
{
case TBLOCK_DEFAULT:
@ -3441,29 +3523,8 @@ AbortCurrentTransaction(void)
AbortSubTransaction();
s->blockState = TBLOCK_SUBABORT;
break;
/*
* If we failed while trying to create a subtransaction, clean up
* the broken subtransaction and abort the parent. The same
* applies if we get a failure while ending a subtransaction.
*/
case TBLOCK_SUBBEGIN:
case TBLOCK_SUBRELEASE:
case TBLOCK_SUBCOMMIT:
case TBLOCK_SUBABORT_PENDING:
case TBLOCK_SUBRESTART:
AbortSubTransaction();
CleanupSubTransaction();
AbortCurrentTransaction();
break;
/*
* Same as above, except the Abort() was already done.
*/
case TBLOCK_SUBABORT_END:
case TBLOCK_SUBABORT_RESTART:
CleanupSubTransaction();
AbortCurrentTransaction();
default:
/* Keep compiler quiet */
break;
}
}

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