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Commit6f38c43

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Avoid stack overflow in ShowTransactionStateRec()
The function recurses, but didn't perform stack-depth checks. It'sjust a debugging aid, so instead of the usual check_stack_depth()call, stop the printing if we'd risk stack overflow.Here's an example of how to test this: (n=1000000; printf "BEGIN;"; for ((i=1;i<=$n;i++)); do printf "SAVEPOINT s$i;"; done; printf "SET log_min_messages = 'DEBUG5'; SAVEPOINT sp;") | psql >/dev/nullIn the passing, swap building the list of child XIDs and recursing toparent. That saves memory while recursing, reducing the risk of out ofmemory errors with lots of subtransactions. The saving is not verysignificant in practice, but this order seems more logical anyway.Report by Egor Chindyaskin and Alexander Lakhin.Discussion:https://www.postgresql.org/message-id/1672760457.940462079%40f306.i.mail.ruAuthor: Heikki LinnakangasReviewed-by: Robert Haas, Andres Freund, Alexander Korotkov
1 parentfefd9a3 commit6f38c43

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1 file changed

+15
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lines changed
  • src/backend/access/transam

1 file changed

+15
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‎src/backend/access/transam/xact.c

Lines changed: 15 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -5583,8 +5583,22 @@ ShowTransactionStateRec(const char *str, TransactionState s)
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{
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StringInfoDatabuf;
55855585

5586-
initStringInfo(&buf);
5586+
if (s->parent)
5587+
{
5588+
/*
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* Since this function recurses, it could be driven to stack overflow.
5590+
* This is just a debugging aid, so we can leave out some details
5591+
* instead of erroring out with check_stack_depth().
5592+
*/
5593+
if (stack_is_too_deep())
5594+
ereport(DEBUG5,
5595+
(errmsg_internal("%s(%d): parent omitted to avoid stack overflow",
5596+
str,s->nestingLevel)));
5597+
else
5598+
ShowTransactionStateRec(str,s->parent);
5599+
}
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5601+
initStringInfo(&buf);
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if (s->nChildXids>0)
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{
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inti;
@@ -5593,10 +5607,6 @@ ShowTransactionStateRec(const char *str, TransactionState s)
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for (i=1;i<s->nChildXids;i++)
55945608
appendStringInfo(&buf," %u",s->childXids[i]);
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}
5596-
5597-
if (s->parent)
5598-
ShowTransactionStateRec(str,s->parent);
5599-
56005610
ereport(DEBUG5,
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(errmsg_internal("%s(%d) name: %s; blockState: %s; state: %s, xid/subid/cid: %u/%u/%u%s%s",
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str,s->nestingLevel,
@@ -5608,7 +5618,6 @@ ShowTransactionStateRec(const char *str, TransactionState s)
56085618
(unsignedint)currentCommandId,
56095619
currentCommandIdUsed ?" (used)" :"",
56105620
buf.data)));
5611-
56125621
pfree(buf.data);
56135622
}
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