这是一个创建于 1602 天前的主题，其中的信息可能已经有所发展或是发生改变。
执行以下代码
create table t(id int primary key);
insert into t values (5),(10);
-- session 1
start transaction;
insert into t values (8);
此时，select * from performance_schema.data_locks的输出是：
+--------+--------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+-----------+-------------+-----------+
| ENGINE | ENGINE_LOCK_ID | ENGINE_TRANSACTION_ID | THREAD_ID | EVENT_ID | OBJECT_SCHEMA | OBJECT_NAME | PARTITION_NAME | SUBPARTITION_NAME | INDEX_NAME | OBJECT_INSTANCE_BEGIN | LOCK_TYPE | LOCK_MODE | LOCK_STATUS | LOCK_DATA |
+--------+--------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+-----------+-------------+-----------+
| INNODB | 139956701343096:1063:139956609693392 | 2070 | 48 | 18 | test | t | NULL | NULL | NULL | 139956609693392 | TABLE | IX | GRANTED | NULL |
+--------+--------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+-----------+-------------+-----------+
session 1 的那个事务只有一个表级别的独占意向锁。
但是执行以下代码之后，
-- session 2
start transaction;
select * from t where id = 8 for share;
select * from performance_schema.data_locks的输出是：
+--------+---------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+
| ENGINE | ENGINE_LOCK_ID | ENGINE_TRANSACTION_ID | THREAD_ID | EVENT_ID | OBJECT_SCHEMA | OBJECT_NAME | PARTITION_NAME | SUBPARTITION_NAME | INDEX_NAME | OBJECT_INSTANCE_BEGIN | LOCK_TYPE | LOCK_MODE | LOCK_STATUS | LOCK_DATA |
+--------+---------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+
| INNODB | 139956701343096:1063:139956609693392 | 2070 | 48 | 18 | test | t | NULL | NULL | NULL | 139956609693392 | TABLE | IX | GRANTED | NULL |
| INNODB | 139956701343096:2:4:4:139956609690400 | 2070 | 49 | 14 | test | t | NULL | NULL | PRIMARY | 139956609690400 | RECORD | X,REC_NOT_GAP | GRANTED | 8 |
| INNODB | 139956701343944:1063:139956609699536 | 421431678054600 | 49 | 14 | test | t | NULL | NULL | NULL | 139956609699536 | TABLE | IS | GRANTED | NULL |
| INNODB | 139956701343944:2:4:4:139956609696624 | 421431678054600 | 49 | 14 | test | t | NULL | NULL | PRIMARY | 139956609696624 | RECORD | S,REC_NOT_GAP | WAITING | 8 |
+--------+---------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+
此时，显示 session 1 的那个事务持有 id 为 8 的那个索引记录的独占锁。但是为什么在第一次输出时没有显示呢？
第 1 条附言 · 2020-07-04 23:20:08 +08:00
在MySQL InnoDB锁介绍及不同SQL语句分别加什么样的锁 - 51CTO.COM中的“五、performance_schema.data_locks中能看到全部的锁吗?”说明了performance_schema.data_locks并未显示全部的锁。
所以只是没有显示出来而已，但是事实上是存在的。
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