MYSQL8。为什么事务 2 在这种情况下被锁定？

Question

准备好了

# ready
CREATE TABLE table_a
(
    id int PRIMARY KEY AUTO_INCREMENT,
    col_1 INT,
    INDEX idx_a (col_1)
) ENGINE = innodb;

id	col_a
1	10
2	15
3	20
4	25

交易 1

START TRANSACTION;

SELECT *
FROM table_a
WHERE col_1 = 15
FOR UPDATE;

交易 2

START TRANSACTION;

# LOCK
INSERT INTO table_a (col_1) VALUES (10);

performance_schema.data_locks;

LOCK_TYPE	LOCK_MODE	LOCK_STATUS	LOCK_DATA
TABLE	IX	GRANTED
RECORD	X	GRANTED	15, 2
RECORD	X,REC_NOT_GAP	GRANTED	2
RECORD	X,GAP	GRANTED	20, 3

我想知道为什么 Transaction2 被锁定

LOCK_MODE=x，LOCK_DATA=15,2不是在11-14范围内吗？

Answer 1

这里需要一个 Insert Intention Lock between (10, 15] on Repeatable reads 隔离级别。还需要在索引idx_a 上锁定col_1 value 15

参考https://dev.mysql.com/doc/refman/8.0/en/innodb-locking.html#innodb-insert-intention-locks