比如，在有些场景，我们需要下线一台slave，我们使用reset slave来清除show slave status \G里边的同步信息，当我们执行完show slave status \G之后，需要可以看到里边的信息。
执行reset slave，其实是把master.info和relay-log.info文件给删除，但是里边的同步信息还在.

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mysql> stop slave;

Query OK, 0 rows affected (0.01 sec)

mysql> reset slave;

Query OK, 0 rows affected (0.06 sec)

mysql> show slave status \G

*************************** 1. row ***************************

Slave_IO_State:

Master_Host: 10.10.10.200

Master_User: repl

Master_Port: 3306

Connect_Retry: 60

Master_Log_File:

Read_Master_Log_Pos: 4

Relay_Log_File: mysql-relay-bin.000001

Relay_Log_Pos: 4

Relay_Master_Log_File:

Slave_IO_Running: No

Slave_SQL_Running: No

Replicate_Do_DB:

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: 0

Relay_Log_Space: 143

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: 0

Last_SQL_Error:

Replicate_Ignore_Server_Ids:

Master_Server_Id: 1

Master_UUID: 4adfcd1d-4059-11e7-9532-080027d597f9

Master_Info_File: mysql.slave_master_info

SQL_Delay: 0

SQL_Remaining_Delay: NULL

Slave_SQL_Running_State:

Master_Retry_Count: 86400

Master_Bind:

Last_IO_Error_Timestamp:

Last_SQL_Error_Timestamp:

Master_SSL_Crl:

Master_SSL_Crlpath:

Retrieved_Gtid_Set:

Executed_Gtid_Set:

Auto_Position: 0

1 row in set (0.00 sec)

如果有人误开始了start slave，同步依然会开始进行，我们需要用以下这个方法清除的更彻底。

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mysql> reset slave all;

Query OK, 0 rows affected (0.00 sec)

mysql> show slave status \G

Empty set (0.00 sec)