Revise the planner's handling of "pseudoconstant" WHERE clauses, that is

clauses containing no variables and no volatile functions.  Such a clause
can be used as a one-time qual in a gating Result plan node, to suppress
plan execution entirely when it is false.  Even when the clause is true,
putting it in a gating node wins by avoiding repeated evaluation of the
clause.  In previous PG releases, query_planner() would do this for
pseudoconstant clauses appearing at the top level of the jointree, but
there was no ability to generate a gating Result deeper in the plan tree.
To fix it, get rid of the special case in query_planner(), and instead
process pseudoconstant clauses through the normal RestrictInfo qual
distribution mechanism.  When a pseudoconstant clause is found attached to
a path node in create_plan(), pull it out and generate a gating Result at
that point.  This requires special-casing pseudoconstants in selectivity
estimation and cost_qual_eval, but on the whole it's pretty clean.
It probably even makes the planner a bit faster than before for the normal
case of no pseudoconstants, since removing pull_constant_clauses saves one
useless traversal of the qual tree.  Per gripe from Phil Frost.

4 files changed, 11 insertions, 10 deletions

diff --git a/src/include/optimizer/clauses.h b/src/include/optimizer/clauses.h
index d384d2fa16d..b7c960e77a3 100644
--- a/src/include/optimizer/clauses.h
+++ b/src/include/optimizer/clauses.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/clauses.h,v 1.83 2006/03/05 15:58:57 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/clauses.h,v 1.84 2006/07/01 18:38:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -61,7 +61,6 @@ extern Relids find_nonnullable_rels(Node *clause);
 
 extern bool is_pseudo_constant_clause(Node *clause);
 extern bool is_pseudo_constant_clause_relids(Node *clause, Relids relids);
-extern List *pull_constant_clauses(List *quals, List **constantQual);
 
 extern bool has_distinct_clause(Query *query);
 extern bool has_distinct_on_clause(Query *query);
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
index f728489be54..3e7f510b28d 100644
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/pathnode.h,v 1.68 2006/06/06 17:59:58 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/pathnode.h,v 1.69 2006/07/01 18:38:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -47,8 +47,7 @@ extern BitmapOrPath *create_bitmap_or_path(PlannerInfo *root,
 extern TidPath *create_tidscan_path(PlannerInfo *root, RelOptInfo *rel,
 					List *tidquals);
 extern AppendPath *create_append_path(RelOptInfo *rel, List *subpaths);
-extern ResultPath *create_result_path(RelOptInfo *rel, Path *subpath,
-				   List *constantqual);
+extern ResultPath *create_result_path(List *quals);
 extern MaterialPath *create_material_path(RelOptInfo *rel, Path *subpath);
 extern UniquePath *create_unique_path(PlannerInfo *root, RelOptInfo *rel,
 				   Path *subpath);
diff --git a/src/include/optimizer/planmain.h b/src/include/optimizer/planmain.h
index 16948801c5d..30b89d0974d 100644
--- a/src/include/optimizer/planmain.h
+++ b/src/include/optimizer/planmain.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/planmain.h,v 1.92 2006/03/05 15:58:57 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/planmain.h,v 1.93 2006/07/01 18:38:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -42,7 +42,6 @@ extern Sort *make_sort_from_sortclauses(PlannerInfo *root, List *sortcls,
 						   Plan *lefttree);
 extern Sort *make_sort_from_groupcols(PlannerInfo *root, List *groupcls,
 						 AttrNumber *grpColIdx, Plan *lefttree);
-extern List *order_qual_clauses(PlannerInfo *root, List *clauses);
 extern Agg *make_agg(PlannerInfo *root, List *tlist, List *qual,
 		 AggStrategy aggstrategy,
 		 int numGroupCols, AttrNumber *grpColIdx,
diff --git a/src/include/optimizer/restrictinfo.h b/src/include/optimizer/restrictinfo.h
index 17978ba6668..86add791604 100644
--- a/src/include/optimizer/restrictinfo.h
+++ b/src/include/optimizer/restrictinfo.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/restrictinfo.h,v 1.36 2006/03/05 15:58:57 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/restrictinfo.h,v 1.37 2006/07/01 18:38:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -20,14 +20,18 @@
 extern RestrictInfo *make_restrictinfo(Expr *clause,
 				  bool is_pushed_down,
 				  bool outerjoin_delayed,
+				  bool pseudoconstant,
 				  Relids required_relids);
 extern List *make_restrictinfo_from_bitmapqual(Path *bitmapqual,
 								  bool is_pushed_down,
 								  bool include_predicates);
 extern bool restriction_is_or_clause(RestrictInfo *restrictinfo);
 extern List *get_actual_clauses(List *restrictinfo_list);
-extern void get_actual_join_clauses(List *restrictinfo_list,
-						List **joinquals, List **otherquals);
+extern List *extract_actual_clauses(List *restrictinfo_list,
+									bool pseudoconstant);
+extern void extract_actual_join_clauses(List *restrictinfo_list,
+							List **joinquals,
+							List **otherquals);
 extern List *remove_redundant_join_clauses(PlannerInfo *root,
 							  List *restrictinfo_list,
 							  bool isouterjoin);