Fix bug #5269: ResetPlanCache mustn't invalidate cached utility statements,

especially not ROLLBACK.  ROLLBACK might need to be executed in an already
aborted transaction, when there is no safe way to revalidate the plan.  But
in general there's no point in marking utility statements invalid, since
they have no plans in the normal sense of the word; so we might as well
work a bit harder here to avoid future revalidation cycles.

Back-patch to 8.4, where the bug was introduced.

src/backend/utils/cache/plancache.c

@@ -35,7 +35,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/cache/plancache.c,v 1.32 2010/01/02 16:57:55 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/cache/plancache.c,v 1.33 2010/01/13 16:56:56 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1068,14 +1068,57 @@ PlanCacheSysCallback(Datum arg, int cacheid, ItemPointer tuplePtr)
 void
 ResetPlanCache(void)
 {
-	ListCell   *lc;
+	ListCell   *lc1;
 
-	foreach(lc, cached_plans_list)
+	foreach(lc1, cached_plans_list)
 	{
-		CachedPlanSource *plansource = (CachedPlanSource *) lfirst(lc);
+		CachedPlanSource *plansource = (CachedPlanSource *) lfirst(lc1);
 		CachedPlan *plan = plansource->plan;
+		ListCell   *lc2;
 
-		if (plan)
-			plan->dead = true;
+		/* No work if it's already invalidated */
+		if (!plan || plan->dead)
+			continue;
+
+		/*
+		 * We *must not* mark transaction control statements as dead,
+		 * particularly not ROLLBACK, because they may need to be executed in
+		 * aborted transactions when we can't revalidate them (cf bug #5269).
+		 * In general there is no point in invalidating utility statements
+		 * since they have no plans anyway.  So mark it dead only if it
+		 * contains at least one non-utility statement.
+		 */
+		if (plan->fully_planned)
+		{
+			/* Search statement list for non-utility statements */
+			foreach(lc2, plan->stmt_list)
+			{
+				PlannedStmt *plannedstmt = (PlannedStmt *) lfirst(lc2);
+
+				Assert(!IsA(plannedstmt, Query));
+				if (IsA(plannedstmt, PlannedStmt))
+				{
+					/* non-utility statement, so invalidate */
+					plan->dead = true;
+					break;		/* out of stmt_list scan */
+				}
+			}
+		}
+		else
+		{
+			/* Search Query list for non-utility statements */
+			foreach(lc2, plan->stmt_list)
+			{
+				Query	   *query = (Query *) lfirst(lc2);
+
+				Assert(IsA(query, Query));
+				if (query->commandType != CMD_UTILITY)
+				{
+					/* non-utility statement, so invalidate */
+					plan->dead = true;
+					break;		/* out of stmt_list scan */
+				}
+			}
+		}
 	}
 }