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Extend code that deduces implied equality clauses to detect whether a

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clause being added to a particular restriction-clause list is redundant
with those already in the list.  This avoids useless work at runtime,
and (perhaps more importantly) keeps the selectivity estimation routines
from generating too-small estimates of numbers of output rows.
Also some minor improvements in OPTIMIZER_DEBUG displays.
This commit is contained in:
Tom Lane
2001-10-18 16:11:42 +00:00
parent 5045004958
commit 6254465d06
9 changed files with 373 additions and 110 deletions
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102
src/backend/optimizer/util/relnode.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/relnode.c,v 1.33 2001/05/20 20:28:19 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/relnode.c,v 1.34 2001/10/18 16:11:42 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -17,6 +17,7 @@
#include "optimizer/cost.h"
#include "optimizer/joininfo.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/plancat.h"
#include "optimizer/tlist.h"
#include "parser/parsetree.h"
@ -24,9 +25,10 @@
static RelOptInfo *make_base_rel(Query *root, int relid);
static List *new_join_tlist(List *tlist, int first_resdomno);
static List *build_joinrel_restrictlist(RelOptInfo *joinrel,
RelOptInfo *outer_rel,
RelOptInfo *inner_rel);
static List *build_joinrel_restrictlist(Query *root,
RelOptInfo *joinrel,
RelOptInfo *outer_rel,
RelOptInfo *inner_rel);
static void build_joinrel_joinlist(RelOptInfo *joinrel,
RelOptInfo *outer_rel,
RelOptInfo *inner_rel);
@ -274,7 +276,8 @@ build_join_rel(Query *root,
* particular pair of component relations.
*/
if (restrictlist_ptr)
*restrictlist_ptr = build_joinrel_restrictlist(joinrel,
*restrictlist_ptr = build_joinrel_restrictlist(root,
joinrel,
outer_rel,
inner_rel);
return joinrel;
@ -326,7 +329,10 @@ build_join_rel(Query *root,
* caller might or might not need the restrictlist, but I need it
* anyway for set_joinrel_size_estimates().)
*/
restrictlist = build_joinrel_restrictlist(joinrel, outer_rel, inner_rel);
restrictlist = build_joinrel_restrictlist(root,
joinrel,
outer_rel,
inner_rel);
if (restrictlist_ptr)
*restrictlist_ptr = restrictlist;
build_joinrel_joinlist(joinrel, outer_rel, inner_rel);
@ -407,6 +413,11 @@ new_join_tlist(List *tlist,
* join paths made from this pair of sub-relations. (It will not need to
* be considered further up the join tree.)
*
* When building a restriction list, we eliminate redundant clauses.
* We don't try to do that for join clause lists, since the join clauses
* aren't really doing anything, just waiting to become part of higher
* levels' restriction lists.
*
* 'joinrel' is a join relation node
* 'outer_rel' and 'inner_rel' are a pair of relations that can be joined
* to form joinrel.
@ -421,19 +432,80 @@ new_join_tlist(List *tlist,
* the original nodes in the lists made for the join relation.
*/
static List *
build_joinrel_restrictlist(RelOptInfo *joinrel,
build_joinrel_restrictlist(Query *root,
RelOptInfo *joinrel,
RelOptInfo *outer_rel,
RelOptInfo *inner_rel)
{
List *result = NIL;
List *rlist;
List *item;
/*
* We must eliminate duplicates, since we will see the same clauses
* arriving from both input relations...
* Collect all the clauses that syntactically belong at this level.
*/
return set_union(subbuild_joinrel_restrictlist(joinrel,
outer_rel->joininfo),
subbuild_joinrel_restrictlist(joinrel,
inner_rel->joininfo));
rlist = nconc(subbuild_joinrel_restrictlist(joinrel,
outer_rel->joininfo),
subbuild_joinrel_restrictlist(joinrel,
inner_rel->joininfo));
/*
* Eliminate duplicate and redundant clauses.
*
* We must eliminate duplicates, since we will see many of the same
* clauses arriving from both input relations. Also, if a clause is
* a mergejoinable clause, it's possible that it is redundant with
* previous clauses (see optimizer/README for discussion). We detect
* that case and omit the redundant clause from the result list.
*
* We can detect redundant mergejoinable clauses very cheaply by using
* their left and right pathkeys, which uniquely identify the sets of
* equijoined variables in question. All the members of a pathkey set
* that are in the left relation have already been forced to be equal;
* likewise for those in the right relation. So, we need to have only
* one clause that checks equality between any set member on the left and
* any member on the right; by transitivity, all the rest are then equal.
*/
foreach(item, rlist)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(item);
/* eliminate duplicates */
if (member(rinfo, result))
continue;
/* check for redundant merge clauses */
if (rinfo->mergejoinoperator != InvalidOid)
{
bool redundant = false;
List *olditem;
cache_mergeclause_pathkeys(root, rinfo);
foreach(olditem, result)
{
RestrictInfo *oldrinfo = (RestrictInfo *) lfirst(olditem);
if (oldrinfo->mergejoinoperator != InvalidOid &&
rinfo->left_pathkey == oldrinfo->left_pathkey &&
rinfo->right_pathkey == oldrinfo->right_pathkey)
{
redundant = true;
break;
}
}
if (redundant)
continue;
}
/* otherwise, add it to result list */
result = lappend(result, rinfo);
}
freeList(rlist);
return result;
}
static void
@ -458,7 +530,6 @@ subbuild_joinrel_restrictlist(RelOptInfo *joinrel,
if (is_subseti(joininfo->unjoined_relids, joinrel->relids))
{
/*
* Clauses in this JoinInfo list become restriction clauses
* for the joinrel, since they refer to no outside rels.
@ -471,7 +542,6 @@ subbuild_joinrel_restrictlist(RelOptInfo *joinrel,
}
else
{
/*
* These clauses are still join clauses at this level, so we
* ignore them in this routine.
@ -497,7 +567,6 @@ subbuild_joinrel_joinlist(RelOptInfo *joinrel,
joinrel->relids);
if (new_unjoined_relids == NIL)
{
/*
* Clauses in this JoinInfo list become restriction clauses
* for the joinrel, since they refer to no outside rels. So we
@ -506,7 +575,6 @@ subbuild_joinrel_joinlist(RelOptInfo *joinrel,
}
else
{
/*
* These clauses are still join clauses at this level, so find
* or make the appropriate JoinInfo item for the joinrel, and