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Commit73f1c17

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Don't use partial unique indexes for unique proofs in the planner
Here we adjust relation_has_unique_index_for() so that it no longer makesuse of partial unique indexes as uniqueness proofs. It is incorrect touse these as the predicates used by check_index_predicates() to setpredOK makes use of not only baserestrictinfo quals as proofs, but alsoqual from join conditions. For relation_has_unique_index_for()'s case, weneed to know the relation is unique for a given set of columns before anyjoins are evaluated, so if predOK was only set to true due to some joinqual, then it's unsafe to use such indexes inrelation_has_unique_index_for(). The final plan may not even make useof that index, which could result in reading tuples that are not asunique as the planner previously expected them to be.Bug: #17975Reported-by: Tor Erik LinnerudBackpatch-through: 11, all supported versionsDiscussion:https://postgr.es/m/17975-98a90c156f25c952%40postgresql.org
1 parent3f157d0 commit73f1c17

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4 files changed

+36
-8
lines changed

4 files changed

+36
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lines changed

‎src/backend/optimizer/path/indxpath.c

Lines changed: 6 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -3569,10 +3569,13 @@ relation_has_unique_index_for(PlannerInfo *root, RelOptInfo *rel,
35693569

35703570
/*
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* If the index is not unique, or not immediately enforced, or if it's
3572-
* a partial index that doesn't match the query, it's useless here.
3572+
* a partial index, it's useless here. We're unable to make use of
3573+
* predOK partial unique indexes due to the fact that
3574+
* check_index_predicates() also makes use of join predicates to
3575+
* determine if the partial index is usable. Here we need proofs that
3576+
* hold true before any joins are evaluated.
35733577
*/
3574-
if (!ind->unique|| !ind->immediate||
3575-
(ind->indpred!=NIL&& !ind->predOK))
3578+
if (!ind->unique|| !ind->immediate||ind->indpred!=NIL)
35763579
continue;
35773580

35783581
/*

‎src/backend/optimizer/plan/analyzejoins.c

Lines changed: 4 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -592,18 +592,17 @@ rel_supports_distinctness(PlannerInfo *root, RelOptInfo *rel)
592592
/*
593593
* For a plain relation, we only know how to prove uniqueness by
594594
* reference to unique indexes. Make sure there's at least one
595-
* suitable unique index. It must be immediately enforced, andif
596-
*it's apartial index, it must match the query.(Keep these
597-
*conditions in sync withrelation_has_unique_index_for!)
595+
* suitable unique index. It must be immediately enforced, andnot a
596+
* partial index.(Keep these conditions in sync with
597+
* relation_has_unique_index_for!)
598598
*/
599599
ListCell*lc;
600600

601601
foreach(lc,rel->indexlist)
602602
{
603603
IndexOptInfo*ind= (IndexOptInfo*)lfirst(lc);
604604

605-
if (ind->unique&&ind->immediate&&
606-
(ind->indpred==NIL||ind->predOK))
605+
if (ind->unique&&ind->immediate&&ind->indpred==NIL)
607606
return true;
608607
}
609608
}

‎src/test/regress/expected/join.out

Lines changed: 17 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -6503,6 +6503,23 @@ left join j2 on j1.id1 = j2.id1 where j1.id2 = 1;
65036503
Output: j2.id1, j2.id2
65046504
(8 rows)
65056505

6506+
create unique index j1_id2_idx on j1(id2) where id2 is not null;
6507+
-- ensure we don't use a partial unique index as unique proofs
6508+
explain (verbose, costs off)
6509+
select * from j1
6510+
inner join j2 on j1.id2 = j2.id2;
6511+
QUERY PLAN
6512+
------------------------------------------
6513+
Nested Loop
6514+
Output: j1.id1, j1.id2, j2.id1, j2.id2
6515+
Join Filter: (j1.id2 = j2.id2)
6516+
-> Seq Scan on public.j2
6517+
Output: j2.id1, j2.id2
6518+
-> Seq Scan on public.j1
6519+
Output: j1.id1, j1.id2
6520+
(7 rows)
6521+
6522+
drop index j1_id2_idx;
65066523
-- validate logic in merge joins which skips mark and restore.
65076524
-- it should only do this if all quals which were used to detect the unique
65086525
-- are present as join quals, and not plain quals.

‎src/test/regress/sql/join.sql

Lines changed: 9 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2263,6 +2263,15 @@ explain (verbose, costs off)
22632263
select*from j1
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left join j2onj1.id1=j2.id1wherej1.id2=1;
22652265

2266+
createunique indexj1_id2_idxon j1(id2)where id2is not null;
2267+
2268+
-- ensure we don't use a partial unique index as unique proofs
2269+
explain (verbose, costs off)
2270+
select*from j1
2271+
inner join j2onj1.id2=j2.id2;
2272+
2273+
dropindex j1_id2_idx;
2274+
22662275
-- validate logic in merge joins which skips mark and restore.
22672276
-- it should only do this if all quals which were used to detect the unique
22682277
-- are present as join quals, and not plain quals.

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