表级锁：分为读锁和写锁:
lock tables table_name read;//其他事务只能读，不能加写锁，要等待更新。
SESSION 50 执行:
mysql> update test set name='ccc' where id=1;
mysql> show full processlist;
+----+---------+----------------------+--------+---------+------+------------------------------+---------------------------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+---------+----------------------+--------+---------+------+------------------------------+---------------------------------------+
| 20 | monitor | 115.236.160.82:56186 | NULL | Sleep | 162 | | NULL |
| 21 | monitor | 115.236.160.82:56187 | NULL | Sleep | 162 | | NULL |
| 23 | monitor | 115.236.160.82:56208 | NULL | Sleep | 43 | | NULL |
| 24 | monitor | 115.236.160.82:56209 | NULL | Sleep | 43 | | NULL |
| 47 | monitor | 115.236.160.82:54858 | NULL | Sleep | 66 | | NULL |
| 48 | monitor | 115.236.160.82:54859 | NULL | Sleep | 67 | | NULL |
| 49 | root | localhost | DEVOPS | Query | 0 | init | show full processlist |
| 50 | root | localhost | DEVOPS | Query | 27 | Waiting for table level lock | update test set name='ccc' where id=1 |
+----+---------+----------------------+--------+---------+------+------------------------------+---------------------------------------+
8 rows in set (0.00 sec)
lock tables table_name write;//其他事务不能读
解锁:
unlock tables;
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行级锁：行锁是对索引加锁
目前对于表级锁查找持有的thread id 没有好的办法
