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Commit4d94b5f

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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 anythinginto or out of the RHS of a SEMI or ANTI join. An example from PiotrStefaniak showed that join_is_legal() wasn't sufficiently enforcing thisrule, so lock it down a little harder.I couldn't find a reasonably simple example of the optimizer trying todo this, so no new regression test. (Piotr's example involved the randomsearch in GEQO accidentally trying an invalid case and triggering a sanitycheck way downstream in clause selectivity estimation, which did not seemlike a sequence of events that would be useful to memorialize in aregression test as-is.)Back-patch to all active branches.
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‎src/backend/optimizer/path/joinrels.c

Lines changed: 9 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -470,10 +470,14 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
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/*
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* Otherwise, the proposed join overlaps the RHS but isn't a valid
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* implementation of this SJ. It might still be a legal join,
473-
* however, if it does not overlap the LHS.
473+
* however, if it does not overlap the LHS. But we never allow
474+
* violations of the RHS of SEMI or ANTI joins. (In practice,
475+
* therefore, only LEFT joins ever allow RHS violation.)
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*/
475-
if (bms_overlap(joinrelids,sjinfo->min_lefthand))
476-
return false;
477+
if (sjinfo->jointype==JOIN_SEMI||
478+
sjinfo->jointype==JOIN_ANTI||
479+
bms_overlap(joinrelids,sjinfo->min_lefthand))
480+
return false;/* invalid join path */
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/*----------
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* 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,
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* Set flag here to check at bottom of loop.
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*----------
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*/
501-
if (sjinfo->jointype!=JOIN_SEMI&&
502-
bms_overlap(rel1->relids,sjinfo->min_righthand)&&
505+
if (bms_overlap(rel1->relids,sjinfo->min_righthand)&&
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bms_overlap(rel2->relids,sjinfo->min_righthand))
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{
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/* both overlap; assume OK */
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}
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else
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{
509-
/* one overlaps, the other doesn't(or it's a semijoin)*/
512+
/* one overlaps, the other doesn't */
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is_valid_inner= false;
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}
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}

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