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Fix set_append_rel_pathlist() to deal intelligently with cases where

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substituting a child rel's output expressions into the appendrel's restriction
clauses yields a pseudoconstant restriction.  We might be able to skip scanning
that child rel entirely (if we get constant FALSE), or generate a one-time
filter.  8.3 more or less accidentally generated plans that weren't completely
stupid in these cases, but that was only because an extra recursive level of
subquery_planner() always occurred and allowed const-simplification to happen.
8.4's ability to pull up appendrel members with non-Var outputs exposes the
fact that we need to work harder here.  Per gripe from Sergey Burladyan.
This commit is contained in:
Tom Lane
2009-07-06 18:26:30 +00:00
parent bf6570abef
commit 9b27eab71c
4 changed files with 114 additions and 58 deletions
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35
src/backend/optimizer/path/allpaths.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.183 2009/06/11 14:48:58 momjian Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.184 2009/07/06 18:26:30 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -29,6 +29,7 @@
#include "optimizer/plancat.h"
#include "optimizer/planner.h"
#include "optimizer/prep.h"
#include "optimizer/restrictinfo.h"
#include "optimizer/var.h"
#include "parser/parse_clause.h"
#include "parser/parsetree.h"
@ -318,6 +319,8 @@ set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
int childRTindex;
RangeTblEntry *childRTE;
RelOptInfo *childrel;
List *childquals;
Node *childqual;
Path *childpath;
ListCell *parentvars;
ListCell *childvars;
@ -342,10 +345,34 @@ set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
* baserestrictinfo quals are needed before we can check for
* constraint exclusion; so do that first and then check to see if we
* can disregard this child.
*
* As of 8.4, the child rel's targetlist might contain non-Var
* expressions, which means that substitution into the quals
* could produce opportunities for const-simplification, and perhaps
* even pseudoconstant quals. To deal with this, we strip the
* RestrictInfo nodes, do the substitution, do const-simplification,
* and then reconstitute the RestrictInfo layer.
*/
childrel->baserestrictinfo = (List *)
adjust_appendrel_attrs((Node *) rel->baserestrictinfo,
appinfo);
childquals = get_all_actual_clauses(rel->baserestrictinfo);
childquals = (List *) adjust_appendrel_attrs((Node *) childquals,
appinfo);
childqual = eval_const_expressions(root, (Node *)
make_ands_explicit(childquals));
if (childqual && IsA(childqual, Const) &&
(((Const *) childqual)->constisnull ||
!DatumGetBool(((Const *) childqual)->constvalue)))
{
/*
* Restriction reduces to constant FALSE or constant NULL after
* substitution, so this child need not be scanned.
*/
set_dummy_rel_pathlist(childrel);
continue;
}
childquals = make_ands_implicit((Expr *) childqual);
childquals = make_restrictinfos_from_actual_clauses(root,
childquals);
childrel->baserestrictinfo = childquals;
if (relation_excluded_by_constraints(root, childrel, childRTE))
{