From 3779f7fd9fed8e77cb02a3ef26ab4311906377ad Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 15 Nov 2002 02:36:53 +0000
Subject: [PATCH] Push qual clauses containing subplans to the back of the qual
 list at each plan node.  Per gripe from Ross Reedstrom.

---
 src/backend/optimizer/plan/createplan.c | 48 +++++++++++++++++++++++--
 1 file changed, 46 insertions(+), 2 deletions(-)

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index cba1b2027d..717fcfa3ce 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/createplan.c,v 1.121 2002/11/06 22:31:24 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/createplan.c,v 1.122 2002/11/15 02:36:53 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -70,6 +70,7 @@ static Node *fix_indxqual_operand(Node *node, int baserelid,
 					 IndexOptInfo *index,
 					 Oid *opclass);
 static List *switch_outer(List *clauses);
+static List *order_qual_clauses(Query *root, List *clauses);
 static void copy_path_costsize(Plan *dest, Path *src);
 static void copy_plan_costsize(Plan *dest, Plan *src);
 static SeqScan *make_seqscan(List *qptlist, List *qpqual, Index scanrelid);
@@ -182,6 +183,9 @@ create_scan_plan(Query *root, Path *best_path)
 	 */
 	scan_clauses = get_actual_clauses(best_path->parent->baserestrictinfo);
 
+	/* Sort clauses into best execution order */
+	scan_clauses = order_qual_clauses(root, scan_clauses);
+
 	switch (best_path->pathtype)
 	{
 		case T_SeqScan:
@@ -359,6 +363,7 @@ create_result_plan(Query *root, ResultPath *best_path)
 {
 	Result	   *plan;
 	List	   *tlist;
+	List	   *constclauses;
 	Plan	   *subplan;
 
 	if (best_path->path.parent)
@@ -371,7 +376,9 @@ create_result_plan(Query *root, ResultPath *best_path)
 	else
 		subplan = NULL;
 
-	plan = make_result(tlist, (Node *) best_path->constantqual, subplan);
+	constclauses = order_qual_clauses(root, best_path->constantqual);
+
+	plan = make_result(tlist, (Node *) constclauses, subplan);
 
 	return plan;
 }
@@ -1212,6 +1219,43 @@ switch_outer(List *clauses)
 	return t_list;
 }
 
+/*
+ * order_qual_clauses
+ *		Given a list of qual clauses that will all be evaluated at the same
+ *		plan node, sort the list into the order we want to check the quals
+ *		in at runtime.
+ *
+ * Ideally the order should be driven by a combination of execution cost and
+ * selectivity, but unfortunately we have so little information about
+ * execution cost of operators that it's really hard to do anything smart.
+ * For now, we just move any quals that contain SubPlan references (but not
+ * InitPlan references) to the end of the list.
+ */
+static List *
+order_qual_clauses(Query *root, List *clauses)
+{
+	List	   *nosubplans;
+	List	   *withsubplans;
+	List	   *l;
+
+	/* No need to work hard if the query is subselect-free */
+	if (!root->hasSubLinks)
+		return clauses;
+
+	nosubplans = withsubplans = NIL;
+	foreach(l, clauses)
+	{
+		Node   *clause = lfirst(l);
+
+		if (contain_subplans(clause))
+			withsubplans = lappend(withsubplans, clause);
+		else
+			nosubplans = lappend(nosubplans, clause);
+	}
+
+	return nconc(nosubplans, withsubplans);
+}
+
 /*
  * Copy cost and size info from a Path node to the Plan node created from it.
  * The executor won't use this info, but it's needed by EXPLAIN.