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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
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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);