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.

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 33a862c8ef61fd2cfdbaa4191c7996e693d2ac5f..562cd39ce8742801e09990664c6c5e21e9508db9 100644 (file)
--- 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 1.215.2.7 2010/01/24 21:49:58 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.215.2.8 2010/07/23 00:43:44 rhaas Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -346,8 +346,35 @@ 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.