replicate-do-db参数引起的MySQL复制错误及处理办法

replicate-do-db配置在MySQL从库的my.cnf文件中，可以指定只复制哪个库的数据。但是这个参数有个问题就是主库如果在其他的schema环境下操作，其binlog不会被从库应用，从而出现异常。可以简单的测试一下 --replicate-do-db参数引起的MySQL复制错误，步骤如下。

从库的my.cnf中有如下配置：

replicate-do-db = maopaodb

首先在主库切换到test这个库并建立maopaodb下的一个表：

mysql> use test;
Database changed

mysql> create table maopaodb.test(id int,name varchar(10));
Query OK, 0 rows affected (0.09 sec)

mysql> use maopaodb;
Database changed
mysql> show tables;

+--------------------------+
| Tables_in_maopaodb |
+--------------------------+
......
| test |
......
+--------------------------+
32 rows in set (0.01 sec)

可见这个表在maopaodb下创建成功，而这时去从库查看，是没有这个表的，因为我们是在test这个库下操作的，而从库的--replicate-do-db指定了maopaodb，因此这些信息不会在从库被应用。

这时主库切换到maopaodb，并写入一条记录：

mysql> use maopaodb;
Database changed
mysql> insert into test values (1,'a');
Query OK, 1 row affected (0.01 sec)

从库这时就会报错了：

mysql> show slave status\G
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.0.33
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000010
Read_Master_Log_Pos: 93731745
Relay_Log_File: mysql-relay-bin.000008
Relay_Log_Pos: 5979038
Relay_Master_Log_File: mysql-bin.000010
Slave_IO_Running: Yes
Slave_SQL_Running: No
Replicate_Do_DB: maopaodb
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno: 1146
Last_Error: Error 'Table 'maopaodb.test' doesn't exist' on query. Default database: 'maopaodb'. Query: 'insert into test values (1,'a')'
Skip_Counter: 0
Exec_Master_Log_Pos: 93709288
Relay_Log_Space: 6001650
Until_Condition: None
Until_Log_File:
Until_Log_Pos: 0
Master_SSL_Allowed: No
Master_SSL_CA_File:
Master_SSL_CA_Path:
Master_SSL_Cert:
Master_SSL_Cipher:
Master_SSL_Key:
Seconds_Behind_Master: NULL
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 1146
Last_SQL_Error: Error 'Table 'maopaodb.test' doesn't exist' on query. Default database: 'maopaodb'. Query: 'insert into test values (1,'a')'
1 row in set (0.00 sec)

对于这种问题复制同步方面的问题，主要都是要在从库这边手动做一些动作，要么补充一些操作，要么跳过一些操作。我们看看如何跳过这个操作。

首先我们要从上边的报错信息关注到以下三点：

Relay_Master_Log_File: mysql-bin.000010

Skip_Counter: 0

Exec_Master_Log_Pos: 93709288

就是我们要明白是主库的哪个日志文件，和日志文件中报错的具体位置，而Skip_Counter参数就是我们要利用的东西。这里我们看到是mysql-bin.000010这个日志文件的93709288位置报错，那么就到主库看看这个位置到底是在执行什么东西：

mysql> SHOW BINLOG EVENTS in 'mysql-bin.000010' from 93709288;
+------------------+----------+------------+-----------+-------------+---------------------------------------------------------------------------------------------------------------------+
| Log_name | Pos | Event_type | Server_id | End_log_pos | Info |
+------------------+----------+------------+-----------+-------------+---------------------------------------------------------------------------------------------------------------------+
| mysql-bin.000010 | 93709288 | Query | 1 | 93709360 | BEGIN |
| mysql-bin.000010 | 93709360 | Query | 1 | 93709458 | use `maopaodb`; insert into test values (1,'a') |
| mysql-bin.000010 | 93709458 | Xid | 1 | 93709485 | COMMIT /* xid=28862936 */ |
| mysql-bin.000010 | 93709485 | Query | 1 | 93709557 | BEGIN |
| mysql-bin.000010 | 93709557 | Query | 1 | 93709723 | use `mogilefs`; UPDATE device SET mb_total = '9564', mb_used = '386', mb_asof = UNIX_TIMESTAMP() WHERE devid = '13' |
| mysql-bin.000010 | 93709723 | Xid | 1 | 93709750 | COMMIT /* xid=28863050 */

......

可见正是导致出错的这个insert语句，MySQL的binary log每个SQL执行实际上是由一些event组成的，我们这里要设置的就是要跳过的event的个数。本例中就是BEGIN、具体SQL语句和COMMIT这3个event，因此我们可以在从库上这样跳过这个语句：

mysql> SET GLOBAL SQL_SLAVE_SKIP_COUNTER = 3;
Query OK, 0 rows affected (0.00 sec)

然后开启同步，一切正常：

mysql> start slave;
Query OK, 0 rows affected (0.00 sec)

mysql> show slave status\G
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.0.33
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000010
Read_Master_Log_Pos: 93733865
Relay_Log_File: mysql-relay-bin.000008
Relay_Log_Pos: 6003615
Relay_Master_Log_File: mysql-bin.000010
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_Do_DB: maopaodb
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno: 0
Last_Error:
Skip_Counter: 0
Exec_Master_Log_Pos: 93733865
Relay_Log_Space: 6003770
Until_Condition: None
Until_Log_File:
Until_Log_Pos: 0
Master_SSL_Allowed: No
Master_SSL_CA_File:
Master_SSL_CA_Path:
Master_SSL_Cert:
Master_SSL_Cipher:
Master_SSL_Key:
Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 0
Last_SQL_Error:
1 row in set (0.00 sec)