线上大表新增字段

正常情况下线上大表新增字段是需要停机的，因为这时候mysql会锁表，任何写操作都会被阻塞。不过如果能保证数据库只读就没问题。

下面是一次线上操作记录，没有对网站造成任何影响。

 

mysql> alter table album_album add `cover` varchar(255) DEFAULT NULL;  
Query OK, 3839848 rows affected (4 min 18.95 sec)
Records: 3839848  Duplicates: 0  Warnings: 0

 

mysql> show processlist;
+----------+-------------+----------------------+-------+-------------+---------+----------------------------------------------------------------+------------------------------------------------------------------------------------------------------+
| Id       | User        | Host                 | db    | Command     | Time    | State                                                          | Info                                                                                                 |
+----------+-------------+----------------------+-------+-------------+---------+----------------------------------------------------------------+------------------------------------------------------------------------------------------------------+
| 70003726 | root        | localhost            | zcwdb | Query       |     161 | copy to tmp table                                              | alter table album_album add `cover` varchar(255) DEFAULT NULL