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？