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Fix cost_mergejoin's failure to adjust for rescanning of non-unique merge join

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keys when considering a semi or anti join.  This requires estimating the
selectivity of the merge qual as though it were a regular inner join condition.
To allow caching both that and the real outer-join-aware selectivity, split
RestrictInfo.this_selec into two fields.

This fixes one of the problems reported by Kevin Grittner.
This commit is contained in:
Tom Lane
2009-02-06 23:43:24 +00:00
parent c87c31f10b
commit c473d92351
9 changed files with 86 additions and 53 deletions
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30
src/backend/optimizer/path/clausesel.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.96 2009/01/01 17:23:43 momjian Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.97 2009/02/06 23:43:23 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -516,21 +516,34 @@ clause_selectivity(PlannerInfo *root,
/*
* If the clause is marked redundant, always return 1.0.
*/
if (rinfo->this_selec > 1)
if (rinfo->norm_selec > 1)
return (Selectivity) 1.0;
/*
* If possible, cache the result of the selectivity calculation for
* the clause. We can cache if varRelid is zero or the clause
* contains only vars of that relid --- otherwise varRelid will affect
* the result, so mustn't cache.
* the result, so mustn't cache. Outer join quals might be examined
* with either their join's actual jointype or JOIN_INNER, so we need
* two cache variables to remember both cases. Note: we assume the
* result won't change if we are switching the input relations or
* considering a unique-ified case, so we only need one cache variable
* for all non-JOIN_INNER cases.
*/
if (varRelid == 0 ||
bms_is_subset_singleton(rinfo->clause_relids, varRelid))
{
/* Cacheable --- do we already have the result? */
if (rinfo->this_selec >= 0)
return rinfo->this_selec;
if (jointype == JOIN_INNER)
{
if (rinfo->norm_selec >= 0)
return rinfo->norm_selec;
}
else
{
if (rinfo->outer_selec >= 0)
return rinfo->outer_selec;
}
cacheable = true;
}
@ -753,7 +766,12 @@ clause_selectivity(PlannerInfo *root,
/* Cache the result if possible */
if (cacheable)
rinfo->this_selec = s1;
{
if (jointype == JOIN_INNER)
rinfo->norm_selec = s1;
else
rinfo->outer_selec = s1;
}
#ifdef SELECTIVITY_DEBUG
elog(DEBUG4, "clause_selectivity: s1 %f", s1);

62
src/backend/optimizer/path/costsize.c
View File

@ -54,7 +54,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.203 2009/01/01 17:23:43 momjian Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.204 2009/02/06 23:43:23 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -120,7 +120,7 @@ static MergeScanSelCache *cached_scansel(PlannerInfo *root,
PathKey *pathkey);
static bool cost_qual_eval_walker(Node *node, cost_qual_eval_context *context);
static double approx_tuple_count(PlannerInfo *root, JoinPath *path,
List *quals, SpecialJoinInfo *sjinfo);
List *quals);
static void set_rel_width(PlannerInfo *root, RelOptInfo *rel);
static double relation_byte_size(double tuples, int width);
static double page_size(double tuples, int width);
@ -1507,11 +1507,9 @@ cost_mergejoin(MergePath *path, PlannerInfo *root, SpecialJoinInfo *sjinfo)
/*
* Get approx # tuples passing the mergequals. We use approx_tuple_count
* here for speed --- in most cases, any errors won't affect the result
* much.
* here because we need an estimate done with JOIN_INNER semantics.
*/
mergejointuples = approx_tuple_count(root, &path->jpath,
mergeclauses, sjinfo);
mergejointuples = approx_tuple_count(root, &path->jpath, mergeclauses);
/*
* When there are equal merge keys in the outer relation, the mergejoin
@ -1539,16 +1537,10 @@ cost_mergejoin(MergePath *path, PlannerInfo *root, SpecialJoinInfo *sjinfo)
* when we should not. Can we do better without expensive selectivity
* computations?
*
* For SEMI and ANTI joins, only one inner tuple need be rescanned for
* each group of same-keyed outer tuples (assuming that all joinquals
* are merge quals). This makes the effect small enough to ignore,
* so we just set rescannedtuples = 0. Likewise, the whole issue is
* moot if we are working from a unique-ified outer input.
* The whole issue is moot if we are working from a unique-ified outer
* input.
*/
if (sjinfo->jointype == JOIN_SEMI ||
sjinfo->jointype == JOIN_ANTI)
rescannedtuples = 0;
else if (IsA(outer_path, UniquePath))
if (IsA(outer_path, UniquePath))
rescannedtuples = 0;
else
{
@ -1847,11 +1839,9 @@ cost_hashjoin(HashPath *path, PlannerInfo *root, SpecialJoinInfo *sjinfo)
/*
* Get approx # tuples passing the hashquals. We use approx_tuple_count
* here for speed --- in most cases, any errors won't affect the result
* much.
* here because we need an estimate done with JOIN_INNER semantics.
*/
hashjointuples = approx_tuple_count(root, &path->jpath,
hashclauses, sjinfo);
hashjointuples = approx_tuple_count(root, &path->jpath, hashclauses);
/* cost of source data */
startup_cost += outer_path->startup_cost;
@ -2324,6 +2314,11 @@ cost_qual_eval_walker(Node *node, cost_qual_eval_context *context)
* The quals can be either an implicitly-ANDed list of boolean expressions,
* or a list of RestrictInfo nodes (typically the latter).
*
* We intentionally compute the selectivity under JOIN_INNER rules, even
* if it's some type of outer join. This is appropriate because we are
* trying to figure out how many tuples pass the initial merge or hash
* join step.
*
* This is quick-and-dirty because we bypass clauselist_selectivity, and
* simply multiply the independent clause selectivities together. Now
* clauselist_selectivity often can't do any better than that anyhow, but
@ -2336,31 +2331,40 @@ cost_qual_eval_walker(Node *node, cost_qual_eval_context *context)
* seems OK to live with the approximation.
*/
static double
approx_tuple_count(PlannerInfo *root, JoinPath *path,
List *quals, SpecialJoinInfo *sjinfo)
approx_tuple_count(PlannerInfo *root, JoinPath *path, List *quals)
{
double tuples;
double outer_tuples = path->outerjoinpath->parent->rows;
double inner_tuples = path->innerjoinpath->parent->rows;
SpecialJoinInfo sjinfo;
Selectivity selec = 1.0;
ListCell *l;
/*
* Make up a SpecialJoinInfo for JOIN_INNER semantics.
*/
sjinfo.type = T_SpecialJoinInfo;
sjinfo.min_lefthand = path->outerjoinpath->parent->relids;
sjinfo.min_righthand = path->innerjoinpath->parent->relids;
sjinfo.syn_lefthand = path->outerjoinpath->parent->relids;
sjinfo.syn_righthand = path->innerjoinpath->parent->relids;
sjinfo.jointype = JOIN_INNER;
/* we don't bother trying to make the remaining fields valid */
sjinfo.lhs_strict = false;
sjinfo.delay_upper_joins = false;
sjinfo.join_quals = NIL;
/* Get the approximate selectivity */
foreach(l, quals)
{
Node *qual = (Node *) lfirst(l);
/* Note that clause_selectivity will be able to cache its result */
selec *= clause_selectivity(root, qual, 0, sjinfo->jointype, sjinfo);
selec *= clause_selectivity(root, qual, 0, JOIN_INNER, &sjinfo);
}
/* Apply it correctly using the input relation sizes */
if (sjinfo->jointype == JOIN_SEMI)
tuples = selec * outer_tuples;
else if (sjinfo->jointype == JOIN_ANTI)
tuples = (1.0 - selec) * outer_tuples;
else
tuples = selec * outer_tuples * inner_tuples;
/* Apply it to the input relation sizes */
tuples = selec * outer_tuples * inner_tuples;
return clamp_row_est(tuples);
}

11
src/backend/optimizer/path/equivclass.c
View File

@ -10,7 +10,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/path/equivclass.c,v 1.16 2009/01/01 17:23:43 momjian Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/path/equivclass.c,v 1.17 2009/02/06 23:43:23 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -1200,7 +1200,8 @@ reconsider_outer_join_clauses(PlannerInfo *root)
list_delete_cell(root->left_join_clauses, cell, prev);
/* we throw it back anyway (see notes above) */
/* but the thrown-back clause has no extra selectivity */
rinfo->this_selec = 2.0;
rinfo->norm_selec = 2.0;
rinfo->outer_selec = 1.0;
distribute_restrictinfo_to_rels(root, rinfo);
}
else
@ -1222,7 +1223,8 @@ reconsider_outer_join_clauses(PlannerInfo *root)
list_delete_cell(root->right_join_clauses, cell, prev);
/* we throw it back anyway (see notes above) */
/* but the thrown-back clause has no extra selectivity */
rinfo->this_selec = 2.0;
rinfo->norm_selec = 2.0;
rinfo->outer_selec = 1.0;
distribute_restrictinfo_to_rels(root, rinfo);
}
else
@ -1244,7 +1246,8 @@ reconsider_outer_join_clauses(PlannerInfo *root)
list_delete_cell(root->full_join_clauses, cell, prev);
/* we throw it back anyway (see notes above) */
/* but the thrown-back clause has no extra selectivity */
rinfo->this_selec = 2.0;
rinfo->norm_selec = 2.0;
rinfo->outer_selec = 1.0;
distribute_restrictinfo_to_rels(root, rinfo);
}
else

9
src/backend/optimizer/path/orindxpath.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/path/orindxpath.c,v 1.86 2009/01/01 17:23:44 momjian Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/path/orindxpath.c,v 1.87 2009/02/06 23:43:23 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -174,10 +174,11 @@ create_or_index_quals(PlannerInfo *root, RelOptInfo *rel)
{
orig_selec = clause_selectivity(root, (Node *) bestrinfo,
0, JOIN_INNER, NULL);
bestrinfo->this_selec = orig_selec / or_selec;
bestrinfo->norm_selec = orig_selec / or_selec;
/* clamp result to sane range */
if (bestrinfo->this_selec > 1)
bestrinfo->this_selec = 1;
if (bestrinfo->norm_selec > 1)
bestrinfo->norm_selec = 1;
/* It isn't an outer join clause, so no need to adjust outer_selec */
}
/* Tell caller to recompute rel's rows estimate */