From ae1b65b5aa17ab96f95f34d258b1cb358f1d9030 Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Fri, 23 Jul 2010 00:43:35 +0000 Subject: [PATCH] Avoid deep recursion when assigning XIDs to multiple levels of subxacts. Backpatch to 8.0. Andres Freund, with cleanup and adjustment for older branches by me. --- src/backend/access/transam/xact.c | 31 +++++++++++++++++++++++++++++-- 1 file changed, 29 insertions(+), 2 deletions(-) diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c index 583f55ddae6..0ec504d26be 100644 --- a/src/backend/access/transam/xact.c +++ b/src/backend/access/transam/xact.c @@ -10,7 +10,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.229.2.7 2010/01/24 21:49:47 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.229.2.8 2010/07/23 00:43:35 rhaas Exp $ * *------------------------------------------------------------------------- */ @@ -351,8 +351,35 @@ AssignSubTransactionId(TransactionState s) Assert(s->parent != NULL); Assert(s->state == TRANS_INPROGRESS); + + /* + * Ensure parent(s) have XIDs, so that a child always has an XID later + * than its parent. Musn't recurse here, or we might get a stack overflow + * if we're at the bottom of a huge stack of subtransactions none of which + * have XIDs yet. + */ if (!TransactionIdIsValid(s->parent->transactionId)) - AssignSubTransactionId(s->parent); + { + TransactionState p = s->parent; + TransactionState *parents; + size_t parentOffset = 0; + + parents = palloc(sizeof(TransactionState) * s->nestingLevel); + while (p != NULL && !TransactionIdIsValid(p->transactionId)) + { + parents[parentOffset++] = p; + p = p->parent; + } + + /* + * This is technically a recursive call, but the recursion will + * never be more than one layer deep. + */ + while (parentOffset != 0) + AssignSubTransactionId(parents[--parentOffset]); + + pfree(parents); + } /* * Generate a new Xid and record it in PG_PROC and pg_subtrans.