From 8f2ec8cc7e3de918988a49302dddc64deca16c02 Mon Sep 17 00:00:00 2001 From: David Rowley Date: Mon, 19 Jun 2023 13:01:29 +1200 Subject: [PATCH] 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 makes use of partial unique indexes as uniqueness proofs. It is incorrect to use these as the predicates used by check_index_predicates() to set predOK makes use of not only baserestrictinfo quals as proofs, but also qual from join conditions. For relation_has_unique_index_for()'s case, we need to know the relation is unique for a given set of columns before any joins are evaluated, so if predOK was only set to true due to some join qual, then it's unsafe to use such indexes in relation_has_unique_index_for(). The final plan may not even make use of that index, which could result in reading tuples that are not as unique as the planner previously expected them to be. Bug: #17975 Reported-by: Tor Erik Linnerud Backpatch-through: 11, all supported versions Discussion: https://postgr.es/m/17975-98a90c156f25c952%40postgresql.org --- src/backend/optimizer/path/indxpath.c | 9 ++++++--- src/backend/optimizer/plan/analyzejoins.c | 9 ++++----- src/test/regress/expected/join.out | 17 +++++++++++++++++ src/test/regress/sql/join.sql | 9 +++++++++ 4 files changed, 36 insertions(+), 8 deletions(-) diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c index b8000da56d9..3800f0cdfb7 100644 --- a/src/backend/optimizer/path/indxpath.c +++ b/src/backend/optimizer/path/indxpath.c @@ -3557,10 +3557,13 @@ relation_has_unique_index_for(PlannerInfo *root, RelOptInfo *rel, /* * If the index is not unique, or not immediately enforced, or if it's - * a partial index that doesn't match the query, it's useless here. + * a partial index, it's useless here. We're unable to make use of + * predOK partial unique indexes due to the fact that + * check_index_predicates() also makes use of join predicates to + * determine if the partial index is usable. Here we need proofs that + * hold true before any joins are evaluated. */ - if (!ind->unique || !ind->immediate || - (ind->indpred != NIL && !ind->predOK)) + if (!ind->unique || !ind->immediate || ind->indpred != NIL) continue; /* diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c index 7ea6e26fecd..34efeee93f9 100644 --- a/src/backend/optimizer/plan/analyzejoins.c +++ b/src/backend/optimizer/plan/analyzejoins.c @@ -600,9 +600,9 @@ rel_supports_distinctness(PlannerInfo *root, RelOptInfo *rel) /* * For a plain relation, we only know how to prove uniqueness by * reference to unique indexes. Make sure there's at least one - * suitable unique index. It must be immediately enforced, and if - * it's a partial index, it must match the query. (Keep these - * conditions in sync with relation_has_unique_index_for!) + * suitable unique index. It must be immediately enforced, and not a + * partial index. (Keep these conditions in sync with + * relation_has_unique_index_for!) */ ListCell *lc; @@ -610,8 +610,7 @@ rel_supports_distinctness(PlannerInfo *root, RelOptInfo *rel) { IndexOptInfo *ind = (IndexOptInfo *) lfirst(lc); - if (ind->unique && ind->immediate && - (ind->indpred == NIL || ind->predOK)) + if (ind->unique && ind->immediate && ind->indpred == NIL) return true; } } diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out index f635d296c27..0eb6339f608 100644 --- a/src/test/regress/expected/join.out +++ b/src/test/regress/expected/join.out @@ -6503,6 +6503,23 @@ left join j2 on j1.id1 = j2.id1 where j1.id2 = 1; Output: j2.id1, j2.id2 (8 rows) +create unique index j1_id2_idx on j1(id2) where id2 is not null; +-- ensure we don't use a partial unique index as unique proofs +explain (verbose, costs off) +select * from j1 +inner join j2 on j1.id2 = j2.id2; + QUERY PLAN +------------------------------------------ + Nested Loop + Output: j1.id1, j1.id2, j2.id1, j2.id2 + Join Filter: (j1.id2 = j2.id2) + -> Seq Scan on public.j2 + Output: j2.id1, j2.id2 + -> Seq Scan on public.j1 + Output: j1.id1, j1.id2 +(7 rows) + +drop index j1_id2_idx; -- validate logic in merge joins which skips mark and restore. -- it should only do this if all quals which were used to detect the unique -- are present as join quals, and not plain quals. diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql index ea9410199e9..5fdacce91df 100644 --- a/src/test/regress/sql/join.sql +++ b/src/test/regress/sql/join.sql @@ -2263,6 +2263,15 @@ explain (verbose, costs off) select * from j1 left join j2 on j1.id1 = j2.id1 where j1.id2 = 1; +create unique index j1_id2_idx on j1(id2) where id2 is not null; + +-- ensure we don't use a partial unique index as unique proofs +explain (verbose, costs off) +select * from j1 +inner join j2 on j1.id2 = j2.id2; + +drop index j1_id2_idx; + -- validate logic in merge joins which skips mark and restore. -- it should only do this if all quals which were used to detect the unique -- are present as join quals, and not plain quals.