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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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7
src/backend/nodes/outfuncs.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.274 2006/04/30 18:30:39 tgl Exp $
* $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.275 2006/07/01 18:38:32 tgl Exp $
*
* NOTES
* Every node type that can appear in stored rules' parsetrees *must*
@ -1107,8 +1107,7 @@ _outResultPath(StringInfo str, ResultPath *node)
_outPathInfo(str, (Path *) node);
WRITE_NODE_FIELD(subpath);
WRITE_NODE_FIELD(constantqual);
WRITE_NODE_FIELD(quals);
}
static void
@ -1185,6 +1184,7 @@ _outPlannerInfo(StringInfo str, PlannerInfo *node)
WRITE_BOOL_FIELD(hasJoinRTEs);
WRITE_BOOL_FIELD(hasOuterJoins);
WRITE_BOOL_FIELD(hasHavingQual);
WRITE_BOOL_FIELD(hasPseudoConstantQuals);
}
static void
@ -1252,6 +1252,7 @@ _outRestrictInfo(StringInfo str, RestrictInfo *node)
WRITE_BOOL_FIELD(is_pushed_down);
WRITE_BOOL_FIELD(outerjoin_delayed);
WRITE_BOOL_FIELD(can_join);
WRITE_BOOL_FIELD(pseudoconstant);
WRITE_BITMAPSET_FIELD(clause_relids);
WRITE_BITMAPSET_FIELD(required_relids);
WRITE_BITMAPSET_FIELD(left_relids);