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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/nodes/copyfuncs.c | |
| parent | 68628fc38ea7a3c72f6a813b0193d836731d9c10 (diff) | |
| download | postgresql-cffd89ca736e485309cd51ae056f837bd7e683ad.tar.gz postgresql-cffd89ca736e485309cd51ae056f837bd7e683ad.zip | |
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/nodes/copyfuncs.c')
| -rw-r--r-- | src/backend/nodes/copyfuncs.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c index 2f2111458e0..6cf580c136c 100644 --- a/src/backend/nodes/copyfuncs.c +++ b/src/backend/nodes/copyfuncs.c @@ -15,7 +15,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.337 2006/06/27 03:43:19 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.338 2006/07/01 18:38:32 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -1264,6 +1264,7 @@ _copyRestrictInfo(RestrictInfo *from) COPY_SCALAR_FIELD(is_pushed_down); COPY_SCALAR_FIELD(outerjoin_delayed); COPY_SCALAR_FIELD(can_join); + COPY_SCALAR_FIELD(pseudoconstant); COPY_BITMAPSET_FIELD(clause_relids); COPY_BITMAPSET_FIELD(required_relids); COPY_BITMAPSET_FIELD(left_relids); |