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Re: Hash-based MCV matching for large IN-lists

Zsolt Parragi <zsolt.parragi@percona.com>

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From: Zsolt Parragi <zsolt.parragi@percona.com>
To: Ilia Evdokimov <ilya.evdokimov@tantorlabs.com>
Cc: Tatsuya Kawata <kawatatatsuya0913@gmail.com>, David Geier <geidav.pg@gmail.com>, Chengpeng Yan <chengpeng_yan@outlook.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2026-02-25T21:39:05Z
Lists: pgsql-hackers 
Hello

+ hashContext.hash_fcinfo = hash_fcinfo;
+ hashContext.op_is_reversed = !hash_mcv;
+ hashContext.insert_mode = true;

Are you sure about op_is_reversed, isn't it backwards, shouldn't it be
= hash_mcv instead?

See the following testcase:

CREATE TABLE test_cross_type_bug (val float4);

INSERT INTO test_cross_type_bug
    SELECT v
      FROM generate_series(1, 200) AS v,
           generate_series(1, 50);

ALTER TABLE test_cross_type_bug ALTER COLUMN val SET STATISTICS 200;
ANALYZE test_cross_type_bug;

SELECT string_agg(v::text, ', ') AS in_list
  FROM generate_series(1, 200) AS gs(v) \gset

EXPLAIN SELECT * FROM test_cross_type_bug
 WHERE val = ANY(ARRAY[:in_list]::float4[]);

EXPLAIN SELECT * FROM test_cross_type_bug
 WHERE val = ANY(ARRAY[:in_list]::float8[]);

DROP TABLE test_cross_type_bug;

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Short-circuit row estimation in NOT IN containing NULL consts