Fix performance problem in fireRIRonSubselect: with nested subqueries,

fireRIRonSubselect was invoked twice at each subselect, leading to an
exponential amount of wasted effort.

diff --git a/src/backend/rewrite/rewriteHandler.c b/src/backend/rewrite/rewriteHandler.c
index 57169d9..0ba42f0 100644 (file)
--- a/src/backend/rewrite/rewriteHandler.c
+++ b/src/backend/rewrite/rewriteHandler.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteHandler.c,v 1.67 2000/01/27 18:11:37 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteHandler.c,v 1.68 2000/03/12 18:57:05 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -958,10 +958,6 @@ fireRIRonSubselect(Node *node, void *context)
                return false;
        if (IsA(node, SubLink))
        {
-               /*
-                * Standard expression_tree_walker will not recurse into subselect,
-                * but here we must do so.
-                */
                SubLink    *sub = (SubLink *) node;
                Query      *qry;
 
@@ -971,14 +967,12 @@ fireRIRonSubselect(Node *node, void *context)
                /* Do what we came for */
                qry = fireRIRrules((Query *) (sub->subselect));
                sub->subselect = (Node *) qry;
-               /* Must recurse to handle any sub-subselects! */
-               if (fireRIRonSubselect((Node *) qry, context))
-                       return true;
+               /* Need not recurse into subselect, because fireRIRrules did it */
                return false;
        }
        if (IsA(node, Query))
        {
-               /* Reach here after recursing down into subselect above... */
+               /* Reach here when called from fireRIRrules */
                Query      *qry = (Query *) node;
 
                if (fireRIRonSubselect((Node *) (qry->targetList), context))
@@ -1107,12 +1101,12 @@ fireRIRrules(Query *parsetree)
                heap_close(rel, AccessShareLock);
        }
 
-       if (parsetree->hasSubLinks)
-               fireRIRonSubselect((Node *) parsetree, NULL);
-
        if (parsetree->hasAggs)
                parsetree->qual = modifyAggrefQual(parsetree->qual, parsetree);
 
+       if (parsetree->hasSubLinks)
+               fireRIRonSubselect((Node *) parsetree, NULL);
+
        return parsetree;
 }