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

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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.
This commit is contained in:
Tom Lane
2006-07-01 18:38:33 +00:00
parent 68628fc38e
commit cffd89ca73
20 changed files with 464 additions and 294 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
src/include/optimizer/clauses.h
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@@ -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);

5
src/include/optimizer/pathnode.h
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@@ -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);

3
src/include/optimizer/planmain.h
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@@ -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,

10
src/include/optimizer/restrictinfo.h
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@@ -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);