From 6af9ee4c8c8f31cbf2e76166d1d9868876f60aea Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 5 Aug 2015 14:39:07 -0400
Subject: [PATCH] Make real sure we don't reassociate joins into or out of
SEMI/ANTI joins.
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.
---
src/backend/optimizer/path/joinrels.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c
index 02c7c5ea864..475241856bd 100644
--- a/src/backend/optimizer/path/joinrels.c
+++ b/src/backend/optimizer/path/joinrels.c
@@ -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;
}
}
--
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