[MDEV-19008] Slow EXPLAIN SELECT ... WHERE col IN (const1,const2,(subquery)) Created: 2019-03-21  Updated: 2019-03-22  Resolved: 2019-03-22

Status: Closed
Project: MariaDB Server
Component/s: Optimizer
Affects Version/s: 10.1, 10.2, 10.3, 10.4
Fix Version/s: 10.3.14, 10.4.4

Type: Bug Priority: Major
Reporter: Alexander Barkov Assignee: Alexander Barkov
Resolution: Fixed Votes: 0
Labels: None

Issue Links:
Blocks
blocks MDEV-18319 BIGINT UNSIGNED Performance issue Stalled
blocks MDEV-18898 SELECT using wrong index when using o... Open

 Description   

I run this script:

DROP TABLE IF EXISTS t1;
CREATE TABLE t1 (a INT);
INSERT INTO t1 VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
EXPLAIN SELECT * FROM t1 WHERE a IN (1,2,(SELECT MAX(a) FROM t1));

+------+-------------+-------+------+---------------+------+---------+------+--------+-------------+
| id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows   | Extra       |
+------+-------------+-------+------+---------------+------+---------+------+--------+-------------+
|    1 | PRIMARY     | t1    | ALL  | NULL          | NULL | NULL    | NULL | 328184 | Using where |
|    2 | SUBQUERY    | t1    | ALL  | NULL          | NULL | NULL    | NULL | 328144 |             |
+------+-------------+-------+------+---------------+------+---------+------+--------+-------------+
2 rows in set (6.69 sec)

Notice, the EXPLAIN query was slow.


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