Fix erroneous memory context switch in autovacuum, which was returning to a

context long after it had been destroyed.

Per problem report from Justin Pasher.  Patch by Tom Lane and me.

8.3 and later do not have this bug, because this code has been restructured for
unrelated reasons.  In 8.2 it does not manifest as a crash, but it still seems
safer fixing it nonetheless.

diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 0e59974b0afed1edfcebf1e67ba89885ba915dd7..31baa5978fb949b9714a5987afdc7f97c58d7af5 100644 (file)
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.5.2.8 2008/01/17 23:47:07 alvherre Exp $
+ *       $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.5.2.9 2009/01/20 12:17:29 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -925,13 +925,12 @@ autovacuum_do_vac_analyze(List *relids, bool dovacuum, bool doanalyze,
                                                  bool freeze)
 {
        VacuumStmt *vacstmt;
-       MemoryContext old_cxt;
 
        /*
         * The node must survive transaction boundaries, so make sure we create it
         * in a long-lived context
         */
-       old_cxt = MemoryContextSwitchTo(AutovacMemCxt);
+       MemoryContextSwitchTo(AutovacMemCxt);
 
        vacstmt = makeNode(VacuumStmt);
 
@@ -957,7 +956,9 @@ autovacuum_do_vac_analyze(List *relids, bool dovacuum, bool doanalyze,
        vacuum(vacstmt, relids);
 
        pfree(vacstmt);
-       MemoryContextSwitchTo(old_cxt);
+
+       /* Make sure we end up pointing to the long-lived context at exit */
+       MemoryContextSwitchTo(AutovacMemCxt);
 }
 
 /*