在 InnoDB 中,为什么不在索引范围内的行会被锁定?

In InnoDB, Why rows which are not in index range are getting locked?

考虑以下查询..

select * from Employee where ID>0 and ID <5.

在执行 explain 时,行数显示为 1。

explain select * from Employee where (ID>0 and ID<5);
+----+-------------+----------+-------+---------------+---------+---------+------+------+-------------+
| id | select_type | table    | type  | possible_keys | key     | key_len | ref  | rows | Extra       |
+----+-------------+----------+-------+---------------+---------+---------+------+------+-------------+
|  1 | SIMPLE      | Employee | range | PRIMARY       | PRIMARY | 8       | NULL |    1 | Using where |
+----+-------------+----------+-------+---------------+---------+---------+------+------+-------------+

但是系统中没有实际的行。

select * from Employee where (ID>0 and ID<5);
Empty set (0.00 sec)

显示引擎 innodb 状态输出:

---TRANSACTION B3D2D, ACTIVE 2109 sec
2 lock struct(s), heap size 376, 1 row lock(s)
MySQL thread id 894932, OS thread handle 0x7f53263e0700, query id 4140397 localhost root

INNODB_LOCKS table 输出:

    +----------------+-------------+-----------+-----------+----------------------+------------+------------+-----------+----------+-----------+
| lock_id        | lock_trx_id | lock_mode | lock_type | lock_table           | lock_index | lock_space | lock_page | lock_rec | lock_data |
+----------------+-------------+-----------+-----------+----------------------+------------+------------+-----------+----------+-----------+
| B42F4:1822:3:7 | B42F4       | X         | RECORD    | `jbossdb`.`Employee` | `PRIMARY`  |       1822 |         3 |        7 | 6         |
| B42ED:1822:3:7 | B42ED       | X         | RECORD    | `jbossdb`.`Employee` | `PRIMARY`  |       1822 |         3 |        7 | 6         |
+----------------+-------------+-----------+-----------+----------------------+------------+------------+-----------+----------+-----------+

INNODB_LOCK_WAITS 输出:

+-------------------+-------------------+-----------------+------------------+
| requesting_trx_id | requested_lock_id | blocking_trx_id | blocking_lock_id |
+-------------------+-------------------+-----------------+------------------+
| B42F4             | B42F4:1822:3:7    | B42ED           | B42ED:1822:3:7   |
+-------------------+-------------------+-----------------+------------------+

PS : 我正在使用 mysql 版本 5.5

有猜想吗?

从 MySQL 8.0.1 开始,您实际上可以看到 innodb 中获取的所有数据锁,它们由性能模式检测:

SELECT * from performance_schema.data_locks;

https://dev.mysql.com/doc/refman/8.0/en/data-locks-table.html

可能相关,来自 8.0.1 发行说明:

InnoDB:在使用 READ COMMITTED 隔离级别时,在外键验证期间不必要地采用了间隙锁。 (漏洞 #25082593)

因此,即使 MySQL 不应该使用 GAP 锁,仍然值得使用性能模式检查实际使用了哪些锁。