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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/path/allpaths.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/optimizer/path/allpaths.c')
| -rw-r--r-- | src/backend/optimizer/path/allpaths.c | 10 |
1 files changed, 6 insertions, 4 deletions
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c index de82c3df8d0..ad55360a853 100644 --- a/src/backend/optimizer/path/allpaths.c +++ b/src/backend/optimizer/path/allpaths.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.146 2006/05/02 04:34:18 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.147 2006/07/01 18:38:32 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -446,7 +446,9 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel, * There are several cases where we cannot push down clauses. Restrictions * involving the subquery are checked by subquery_is_pushdown_safe(). * Restrictions on individual clauses are checked by - * qual_is_pushdown_safe(). + * qual_is_pushdown_safe(). Also, we don't want to push down + * pseudoconstant clauses; better to have the gating node above the + * subquery. * * Non-pushed-down clauses will get evaluated as qpquals of the * SubqueryScan node. @@ -466,7 +468,8 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel, RestrictInfo *rinfo = (RestrictInfo *) lfirst(l); Node *clause = (Node *) rinfo->clause; - if (qual_is_pushdown_safe(subquery, rti, clause, differentTypes)) + if (!rinfo->pseudoconstant && + qual_is_pushdown_safe(subquery, rti, clause, differentTypes)) { /* Push it down */ subquery_push_qual(subquery, rte, rti, clause); @@ -1066,7 +1069,6 @@ print_path(PlannerInfo *root, Path *path, int indent) break; case T_ResultPath: ptype = "Result"; - subpath = ((ResultPath *) path)->subpath; break; case T_MaterialPath: ptype = "Material"; |