From 9e77323fccff6a084115cde3641dbcee86624f14 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Thu, 27 Nov 2025 13:09:59 -0500 Subject: [PATCH] Allow indexscans on partial hash indexes with implied quals. Normally, if a WHERE clause is implied by the predicate of a partial index, we drop that clause from the set of quals used with the index, since it's redundant to test it if we're scanning that index. However, if it's a hash index (or any !amoptionalkey index), this could result in dropping all available quals for the index's first key, preventing us from generating an indexscan. It's fair to question the practical usefulness of this case. Since hash only supports equality quals, the situation could only arise if the index's predicate is "WHERE indexkey = constant", implying that the index contains only one hash value, which would make hash a really poor choice of index type. However, perhaps there are other !amoptionalkey index AMs out there with which such cases are more plausible. To fix, just don't filter the candidate indexquals this way if the index is !amoptionalkey. That's a bit hokey because it may result in testing quals we didn't need to test, but to do it more accurately we'd have to redundantly identify which candidate quals are actually usable with the index, something we don't know at this early stage of planning. Doesn't seem worth the effort. Reported-by: Sergei Glukhov Author: Tom Lane Reviewed-by: David Rowley Discussion: https://postgr.es/m/e200bf38-6b45-446a-83fd-48617211feff@postgrespro.ru Backpatch-through: 14 --- src/backend/optimizer/path/indxpath.c | 10 ++++++++++ src/test/regress/expected/create_index.out | 2 ++ src/test/regress/expected/hash_index.out | 19 +++++++++++++++++++ src/test/regress/sql/create_index.sql | 3 +++ src/test/regress/sql/hash_index.sql | 10 ++++++++++ 5 files changed, 44 insertions(+) diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c index 8c395be3456..2ba687c3256 100644 --- a/src/backend/optimizer/path/indxpath.c +++ b/src/backend/optimizer/path/indxpath.c @@ -3424,6 +3424,16 @@ check_index_predicates(PlannerInfo *root, RelOptInfo *rel) if (is_target_rel) continue; + /* + * If index is !amoptionalkey, also leave indrestrictinfo as set + * above. Otherwise we risk removing all quals for the first index + * key and then not being able to generate an indexscan at all. It + * would be better to be more selective, but we've not yet identified + * which if any of the quals match the first index key. + */ + if (!index->amoptionalkey) + continue; + /* Else compute indrestrictinfo as the non-implied quals */ index->indrestrictinfo = NIL; foreach(lcr, rel->baserestrictinfo) diff --git a/src/test/regress/expected/create_index.out b/src/test/regress/expected/create_index.out index 74507ebd217..be80774dd4f 100644 --- a/src/test/regress/expected/create_index.out +++ b/src/test/regress/expected/create_index.out @@ -1271,6 +1271,8 @@ CREATE INDEX hash_i4_index ON hash_i4_heap USING hash (random int4_ops); CREATE INDEX hash_name_index ON hash_name_heap USING hash (random name_ops); CREATE INDEX hash_txt_index ON hash_txt_heap USING hash (random text_ops); CREATE INDEX hash_f8_index ON hash_f8_heap USING hash (random float8_ops) WITH (fillfactor=60); +CREATE INDEX hash_i4_partial_index ON hash_i4_heap USING hash (seqno) + WHERE seqno = 9999; CREATE UNLOGGED TABLE unlogged_hash_table (id int4); CREATE INDEX unlogged_hash_index ON unlogged_hash_table USING hash (id int4_ops); DROP TABLE unlogged_hash_table; diff --git a/src/test/regress/expected/hash_index.out b/src/test/regress/expected/hash_index.out index e23de21b41c..19bb94921fd 100644 --- a/src/test/regress/expected/hash_index.out +++ b/src/test/regress/expected/hash_index.out @@ -82,6 +82,25 @@ SELECT * FROM hash_f8_heap -------+-------- (0 rows) +-- +-- partial hash index +-- +EXPLAIN (COSTS OFF) +SELECT * FROM hash_i4_heap + WHERE seqno = 9999; + QUERY PLAN +-------------------------------------------------------- + Index Scan using hash_i4_partial_index on hash_i4_heap + Index Cond: (seqno = 9999) +(2 rows) + +SELECT * FROM hash_i4_heap + WHERE seqno = 9999; + seqno | random +-------+------------ + 9999 | 1227676208 +(1 row) + -- -- hash index -- grep '^90[^0-9]' hashovfl.data diff --git a/src/test/regress/sql/create_index.sql b/src/test/regress/sql/create_index.sql index fc73301679a..b4c49405ae2 100644 --- a/src/test/regress/sql/create_index.sql +++ b/src/test/regress/sql/create_index.sql @@ -374,6 +374,9 @@ CREATE INDEX hash_txt_index ON hash_txt_heap USING hash (random text_ops); CREATE INDEX hash_f8_index ON hash_f8_heap USING hash (random float8_ops) WITH (fillfactor=60); +CREATE INDEX hash_i4_partial_index ON hash_i4_heap USING hash (seqno) + WHERE seqno = 9999; + CREATE UNLOGGED TABLE unlogged_hash_table (id int4); CREATE INDEX unlogged_hash_index ON unlogged_hash_table USING hash (id int4_ops); DROP TABLE unlogged_hash_table; diff --git a/src/test/regress/sql/hash_index.sql b/src/test/regress/sql/hash_index.sql index 4d1aa020a96..cf05ec02751 100644 --- a/src/test/regress/sql/hash_index.sql +++ b/src/test/regress/sql/hash_index.sql @@ -55,6 +55,16 @@ SELECT * FROM hash_f8_heap SELECT * FROM hash_f8_heap WHERE hash_f8_heap.random = '88888888'::float8; +-- +-- partial hash index +-- +EXPLAIN (COSTS OFF) +SELECT * FROM hash_i4_heap + WHERE seqno = 9999; + +SELECT * FROM hash_i4_heap + WHERE seqno = 9999; + -- -- hash index -- grep '^90[^0-9]' hashovfl.data -- 2.39.5