一主一从切换示例

1.修改配置文件
master 配置文件
innodb_flush_log_at_trx_commit=1
sync_binlog=1
read_only=1


slave 配置文件
innodb_flush_log_at_trx_commit=1
sync_binlog=1
#read_only=1

2.查询主，从库的状态
--master
 mysql>  show processlist \G
 *************************** 1. row ***************************
      Id: 9
    User: root
    Host: localhost
      db: test
 Command: Sleep
    Time: 576
   State:
    Info: NULL
 *************************** 2. row ***************************
      Id: 13
    User: repl
    Host: 192.168.1.106:41457
      db: NULL
 Command: Binlog Dump
    Time: 404
   State: Master has sent all binlog to slave; waiting for binlog to be updated
    Info: NULL
 *************************** 3. row ***************************
      Id: 15
    User: root
    Host: localhost
      db: test
 Command: Query
    Time: 0
   State: NULL
    Info: show processlist
 3 rows in set (0.01 sec)
 
 mysql> show master status \G
 *************************** 1. row ***************************
             File: mysql-bin.000007
         Position: 2940
     Binlog_Do_DB:
 Binlog_Ignore_DB:
 1 row in set (0.00 sec)

--slave
 mysql>  show processlist \G
 *************************** 1. row ***************************
      Id: 1
    User: system user
    Host:
      db: NULL
 Command: Connect
    Time: 353
   State: Waiting for master to send event
    Info: NULL
 *************************** 2. row ***************************
      Id: 2
    User: system user
    Host:
      db: NULL
 Command: Connect
    Time: 35
   State: Slave has read all relay log; waiting for the slave I/O thread to update it
    Info: NULL
 *************************** 3. row ***************************
      Id: 4
    User: root
    Host: localhost
      db: NULL
 Command: Query
    Time: 0
   State: NULL
    Info: show processlist
 3 rows in set (0.00 sec)
 
 mysql> show slave status \G
 *************************** 1. row ***************************
                Slave_IO_State: Waiting for master to send event
                   Master_Host: 192.168.1.107
                   Master_User: repl
                   Master_Port: 3306
                 Connect_Retry: 60
               Master_Log_File: mysql-bin.000007
           Read_Master_Log_Pos: 2940
                Relay_Log_File: master-relay-bin.000012
                 Relay_Log_Pos: 1026
         Relay_Master_Log_File: mysql-bin.000007
              Slave_IO_Running: Yes
             Slave_SQL_Running: Yes
               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: 2940
               Relay_Log_Space: 1183
               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:
   Replicate_Ignore_Server_Ids:
              Master_Server_Id: 2
 1 row in set (0.00 sec)

3.主库置只读状态
--master
mysql> set global read_only=1;

4.再次查看主，从状态，从接收完所有日志后,停止io线程
--slave
mysql> stop slave io_thread;
Query OK, 0 rows affected (0.00 sec)
mysql>  show processlist \G
mysql> show slave status \G

Make sure that the slave have processed any statements in their relay log.
show processlist \G中显示 State: Slave has read all relay log;

5.从库置为主库
--slave
mysql> stop slave;
Query OK, 0 rows affected (0.00 sec)

mysql> reset master;
Query OK, 0 rows affected (0.01 sec)

mysql> reset slave;
Query OK, 0 rows affected (0.01 sec)

mysql> show master status \G
*************************** 1. row ***************************
            File: mysql-bin.000001
        Position: 107
    Binlog_Do_DB:
Binlog_Ignore_DB:
1 row in set (0.00 sec)
mysql> set global read_only=0;

6.主库置为从库
mysql> reset master;
Query OK, 0 rows affected (0.01 sec)

mysql>  CHANGE MASTER TO
    ->         MASTER_HOST='master',
    ->         MASTER_USER='repl',
    ->         MASTER_PASSWORD='repl',
    ->         MASTER_LOG_FILE='mysql-bin.000001',
    ->         MASTER_LOG_POS=107;
Query OK, 0 rows affected (0.03 sec)

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: master
                  Master_User: repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000001
          Read_Master_Log_Pos: 107
               Relay_Log_File: slave1-relay-bin.000002
                Relay_Log_Pos: 253
        Relay_Master_Log_File: mysql-bin.000001
             Slave_IO_Running: Yes
            Slave_SQL_Running: Yes
              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: 107
              Relay_Log_Space: 410
              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:
  Replicate_Ignore_Server_Ids:
             Master_Server_Id: 1
1 row in set (0.00 sec)