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Fix a thinko in join_is_legal: when we decide we can implement a semijoin

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by unique-ifying the RHS and then inner-joining to some other relation,
that is not grounds for violating the RHS of some other outer join.
Noticed while regression-testing new GEQO code, which will blindly follow
any path that join_is_legal says is legal, and then complain later if that
leads to a dead end.

I'm not certain that this can result in any visible failure in 8.4: the
mistake may always be masked by the fact that subsequent attempts to join
the rest of the RHS of the other join will fail.  But I'm not certain it
can't, either, and it's definitely not operating as intended.  So back-patch.

The added regression test depends on the new no-failures-allowed logic
that I'm about to commit in GEQO, so no point back-patching that.
This commit is contained in:
Tom Lane 2009-07-19 20:32:56 +00:00
parent 683706b136
commit 7197706d81
1 changed files with 12 additions and 3 deletions
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15
src/backend/optimizer/path/joinrels.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/path/joinrels.c,v 1.100 2009/06/11 14:48:59 momjian Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/path/joinrels.c,v 1.100.2.1 2009/07/19 20:32:56 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -349,6 +349,7 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
{
SpecialJoinInfo *match_sjinfo;
bool reversed;
bool unique_ified;
bool is_valid_inner;
ListCell *l;
@ -366,6 +367,7 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
*/
match_sjinfo = NULL;
reversed = false;
unique_ified = false;
is_valid_inner = true;
foreach(l, root->join_info_list)
@ -450,6 +452,7 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
return false; /* invalid join path */
match_sjinfo = sjinfo;
reversed = false;
unique_ified = true;
}
else if (sjinfo->jointype == JOIN_SEMI &&
bms_equal(sjinfo->syn_righthand, rel1->relids) &&
@ -461,6 +464,7 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
return false; /* invalid join path */
match_sjinfo = sjinfo;
reversed = true;
unique_ified = true;
}
else
{
@ -510,8 +514,13 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
}
}
/* Fail if violated some SJ's RHS and didn't match to another SJ */
if (match_sjinfo == NULL && !is_valid_inner)
/*
* Fail if violated some SJ's RHS and didn't match to another SJ.
* However, "matching" to a semijoin we are implementing by
* unique-ification doesn't count (think: it's really an inner join).
*/
if (!is_valid_inner &&
(match_sjinfo == NULL || unique_ified))
return false; /* invalid join path */
/* Otherwise, it's a valid join */