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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2006-07-01 18:38:33 +0000 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2006-07-01 18:38:33 +0000 |
| commit | cffd89ca736e485309cd51ae056f837bd7e683ad (patch) | |
| tree | 7ebf13ae5d921d074382d80be66a8d97e7a822e1 /src/backend/optimizer/plan/planner.c | |
| parent | 68628fc38ea7a3c72f6a813b0193d836731d9c10 (diff) | |
| download | postgresql-cffd89ca736e485309cd51ae056f837bd7e683ad.tar.gz | |
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.
Diffstat (limited to 'src/backend/optimizer/plan/planner.c')
| -rw-r--r-- | src/backend/optimizer/plan/planner.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c index da1cadcd0d..160310c56d 100644 --- a/src/backend/optimizer/plan/planner.c +++ b/src/backend/optimizer/plan/planner.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.200 2006/06/28 20:04:38 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.201 2006/07/01 18:38:33 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -270,6 +270,9 @@ subquery_planner(Query *parse, double tuple_fraction, */ root->hasHavingQual = (parse->havingQual != NULL); + /* Clear this flag; might get set in distribute_qual_to_rels */ + root->hasPseudoConstantQuals = false; + /* * Do expression preprocessing on targetlist and quals. */ |