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Fix planner to do the right thing when a degenerate outer join (one whose

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joinclause doesn't use any outer-side vars) requires a "bushy" plan to be
created.  The normal heuristic to avoid joins with no joinclause has to be
overridden in that case.  Problem is new in 8.2; before that we forced the
outer join order anyway.  Per example from Teodor.
This commit is contained in:
Tom Lane
2006-12-12 21:31:02 +00:00
parent 0afabecbfd
commit f18c57fdf1
4 changed files with 52 additions and 11 deletions
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39
src/backend/optimizer/util/joininfo.c
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@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/joininfo.c,v 1.44 2006/03/05 15:58:31 momjian Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/joininfo.c,v 1.45 2006/12/12 21:31:02 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -24,7 +24,8 @@
* the two given relations.
*/
bool
have_relevant_joinclause(RelOptInfo *rel1, RelOptInfo *rel2)
have_relevant_joinclause(PlannerInfo *root,
RelOptInfo *rel1, RelOptInfo *rel2)
{
bool result = false;
Relids join_relids;
@@ -53,6 +54,40 @@ have_relevant_joinclause(RelOptInfo *rel1, RelOptInfo *rel2)
}
}
/*
* It's possible that the rels correspond to the left and right sides
* of a degenerate outer join, that is, one with no joinclause mentioning
* the non-nullable side. The above scan will then have failed to locate
* any joinclause indicating we should join, but nonetheless we must
* allow the join to occur.
*
* Note: we need no comparable check for IN-joins because we can handle
* sequential buildup of an IN-join to multiple outer-side rels; therefore
* the "last ditch" case in make_rels_by_joins() always succeeds. We
* could dispense with this hack if we were willing to try bushy plans
* in the "last ditch" case, but that seems too expensive.
*/
if (!result)
{
foreach(l, root->oj_info_list)
{
OuterJoinInfo *ojinfo = (OuterJoinInfo *) lfirst(l);
/* ignore full joins --- other mechanisms handle them */
if (ojinfo->is_full_join)
continue;
if ((bms_is_subset(ojinfo->min_lefthand, rel1->relids) &&
bms_is_subset(ojinfo->min_righthand, rel2->relids)) ||
(bms_is_subset(ojinfo->min_lefthand, rel2->relids) &&
bms_is_subset(ojinfo->min_righthand, rel1->relids)))
{
result = true;
break;
}
}
}
bms_free(join_relids);
return result;