初识MDL锁
会话1
mysql> begin ;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from tab02;
+----+------+
| id | name |
+----+------+
| 1 | A |
| 3 | A |
| 5 | C |
| 7 | G |
| 10 | I |
+----+------+
5 rows in set (0.00 sec)
会话2
直接执行drop table 操作
mysql> drop table tab02;
hang住
会话3确认当前数据库中的锁
mysql> show processlist;
+----+------+-----------+-------+---------+-------+---------------------------------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+-------+---------+-------+---------------------------------+------------------+
| 1 | root | localhost | myown | Query | 0 | init | show processlist |
| 2 | root | localhost | myown | Query | 152 | Waiting for table metadata lock | drop table tab02 |
| 3 | root | localhost | myown | Sleep | 14125 | | NULL |
+----+------+-----------+-------+---------+-------+---------------------------------+------------------+
drop table tab02操作在等待一个metadata lock，哈哈 搞笑
线上环境尽量不做DDL操作
创建时间：2021-12-22 10:57
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