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Make real sure we don't reassociate joins into or out of SEMI/ANTI joins.

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Per the discussion in optimizer/README, it's unsafe to reassociate anything
into or out of the RHS of a SEMI or ANTI join.  An example from Piotr
Stefaniak showed that join_is_legal() wasn't sufficiently enforcing this
rule, so lock it down a little harder.

I couldn't find a reasonably simple example of the optimizer trying to
do this, so no new regression test.  (Piotr's example involved the random
search in GEQO accidentally trying an invalid case and triggering a sanity
check way downstream in clause selectivity estimation, which did not seem
like a sequence of events that would be useful to memorialize in a
regression test as-is.)

Back-patch to all active branches.
This commit is contained in:
Tom Lane 2015-08-05 14:39:07 -04:00
parent 34a4318e7d
commit 06663971bb
1 changed files with 9 additions and 6 deletions
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15
src/backend/optimizer/path/joinrels.c
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@ -470,10 +470,14 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
/*
* Otherwise, the proposed join overlaps the RHS but isn't a valid
* implementation of this SJ. It might still be a legal join,
* however, if it does not overlap the LHS.
* however, if it does not overlap the LHS. But we never allow
* violations of the RHS of SEMI or ANTI joins. (In practice,
* therefore, only LEFT joins ever allow RHS violation.)
*/
if (bms_overlap(joinrelids, sjinfo->min_lefthand))
return false;
if (sjinfo->jointype == JOIN_SEMI ||
sjinfo->jointype == JOIN_ANTI ||
bms_overlap(joinrelids, sjinfo->min_lefthand))
return false; /* invalid join path */
/*----------
* If both inputs overlap the RHS, assume that it's OK. Since the
@ -498,15 +502,14 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
* Set flag here to check at bottom of loop.
*----------
*/
if (sjinfo->jointype != JOIN_SEMI &&
bms_overlap(rel1->relids, sjinfo->min_righthand) &&
if (bms_overlap(rel1->relids, sjinfo->min_righthand) &&
bms_overlap(rel2->relids, sjinfo->min_righthand))
{
/* both overlap; assume OK */
}
else
{
/* one overlaps, the other doesn't (or it's a semijoin) */
/* one overlaps, the other doesn't */
is_valid_inner = false;
}
}