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Fix set_joinrel_size_estimates() to estimate outer-join sizes more 

accurately: we have to distinguish the effects of the join's own ON
clauses from the effects of pushed-down clauses.  Failing to do so
was a quick hack long ago, but it's time to be smarter.  Per example
from Thomas H.
This commit is contained in:
Tom Lane 2006-11-10 01:21:41 +00:00
parent dcbdf9b1d4
commit d19798e584
1 changed files with 61 additions and 17 deletions
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78
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 1.167 2006/10/04 00:29:53 momjian Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.168 2006/11/10 01:21:41 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -1948,7 +1948,8 @@ set_joinrel_size_estimates(PlannerInfo *root, RelOptInfo *rel,
JoinType jointype,
List *restrictlist)
{
Selectivity selec;
Selectivity jselec;
Selectivity pselec;
double nrows;
UniquePath *upath;
@ -1957,20 +1958,60 @@ set_joinrel_size_estimates(PlannerInfo *root, RelOptInfo *rel,
* clauses that become restriction clauses at this join level; we are not
* double-counting them because they were not considered in estimating the
* sizes of the component rels.
*
* For an outer join, we have to distinguish the selectivity of the
* join's own clauses (JOIN/ON conditions) from any clauses that were
* "pushed down". For inner joins we just count them all as joinclauses.
*/
selec = clauselist_selectivity(root,
restrictlist,
0,
jointype);
if (IS_OUTER_JOIN(jointype))
{
List *joinquals = NIL;
List *pushedquals = NIL;
ListCell *l;
/* Grovel through the clauses to separate into two lists */
foreach(l, restrictlist)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
Assert(IsA(rinfo, RestrictInfo));
if (rinfo->is_pushed_down)
pushedquals = lappend(pushedquals, rinfo);
else
joinquals = lappend(joinquals, rinfo);
}
/* Get the separate selectivities */
jselec = clauselist_selectivity(root,
joinquals,
0,
jointype);
pselec = clauselist_selectivity(root,
pushedquals,
0,
jointype);
/* Avoid leaking a lot of ListCells */
list_free(joinquals);
list_free(pushedquals);
}
else
{
jselec = clauselist_selectivity(root,
restrictlist,
0,
jointype);
pselec = 0.0; /* not used, keep compiler quiet */
}
/*
* Basically, we multiply size of Cartesian product by selectivity.
*
* If we are doing an outer join, take that into account: the output must
* be at least as large as the non-nullable input. (Is there any chance
* of being even smarter?) (XXX this is not really right, because it
* assumes all the restriction clauses are join clauses; we should figure
* pushed-down clauses separately.)
* If we are doing an outer join, take that into account: the joinqual
* selectivity has to be clamped using the knowledge that the output must
* be at least as large as the non-nullable input. However, any
* pushed-down quals are applied after the outer join, so their
* selectivity applies fully.
*
* For JOIN_IN and variants, the Cartesian product is figured with respect
* to a unique-ified input, and then we can clamp to the size of the other
@ -1979,30 +2020,33 @@ set_joinrel_size_estimates(PlannerInfo *root, RelOptInfo *rel,
switch (jointype)
{
case JOIN_INNER:
nrows = outer_rel->rows * inner_rel->rows * selec;
nrows = outer_rel->rows * inner_rel->rows * jselec;
break;
case JOIN_LEFT:
nrows = outer_rel->rows * inner_rel->rows * selec;
nrows = outer_rel->rows * inner_rel->rows * jselec;
if (nrows < outer_rel->rows)
nrows = outer_rel->rows;
nrows *= pselec;
break;
case JOIN_RIGHT:
nrows = outer_rel->rows * inner_rel->rows * selec;
nrows = outer_rel->rows * inner_rel->rows * jselec;
if (nrows < inner_rel->rows)
nrows = inner_rel->rows;
nrows *= pselec;
break;
case JOIN_FULL:
nrows = outer_rel->rows * inner_rel->rows * selec;
nrows = outer_rel->rows * inner_rel->rows * jselec;
if (nrows < outer_rel->rows)
nrows = outer_rel->rows;
if (nrows < inner_rel->rows)
nrows = inner_rel->rows;
nrows *= pselec;
break;
case JOIN_IN:
case JOIN_UNIQUE_INNER:
upath = create_unique_path(root, inner_rel,
inner_rel->cheapest_total_path);
nrows = outer_rel->rows * upath->rows * selec;
nrows = outer_rel->rows * upath->rows * jselec;
if (nrows > outer_rel->rows)
nrows = outer_rel->rows;
break;
@ -2010,7 +2054,7 @@ set_joinrel_size_estimates(PlannerInfo *root, RelOptInfo *rel,
case JOIN_UNIQUE_OUTER:
upath = create_unique_path(root, outer_rel,
outer_rel->cheapest_total_path);
nrows = upath->rows * inner_rel->rows * selec;
nrows = upath->rows * inner_rel->rows * jselec;
if (nrows > inner_rel->rows)
nrows = inner_rel->rows;
break;