MySQL高可用方案MHA在线切换的步骤及原理

今天药忘吃喽~ 2023-01-08 10:25 87阅读 0赞

在日常工作中，会碰到如下的场景，如mysql数据库升级，主服务器硬件升级等，这个时候就需要将写操作切换到另外一台服务器上，那么如何进行在线切换呢？同时，要求切换过程短，对业务的影响比较小。

MHA就提供了这样一种优雅的方式，只会堵塞业务0.5~2s的时间，在这段时间内，业务无法读取和写入。

**集群信息**

角色                             IP地址                 ServerID      类型

Master                         192.168.244.10   1                 写入

Candicate master          192.168.244.20   2                 读

Slave                           192.168.244.30   3                 读

Monitor host                 192.168.244.40                      监控集群组

MHA具体的搭建步骤和原理，可参考另外一篇博客：

[MySQL高可用方案MHA的部署和原理][MySQL_MHA]

**在线切换的步骤**

1. 关闭MHA监控

\# masterha\_stop --conf=/etc/masterha/app1.cnf

2. 在线切换

\# /usr/local/bin/masterha\_master\_switch --conf=/etc/masterha/app1.cnf --master\_state=alive --new\_master\_host=192.168.244.20 --new\_master\_port=3306 --orig\_master\_is\_new\_slave --running\_updates\_limit=10000

其中，

\--orig\_master\_is\_new\_slave是将原master切换为新主的slave，默认情况下，是不添加的。

\--running\_updates\_limit默认为1s，即如果主从延迟时间（Seconds\_Behind\_Master），或master show processlist中dml操作大于1s，则不会执行切换。

**在线切换的输出**

![复制代码][48304ba5e6f9fe08f3fa1abda7d326ab.png]

Tue Apr 11 15:28:32 2017 - [info] MHA::MasterRotate version 0.56.
    Tue Apr 11 15:28:32 2017 - [info] Starting online master switch..
    Tue Apr 11 15:28:32 2017 - [info] 
    Tue Apr 11 15:28:32 2017 - [info] * Phase 1: Configuration Check Phase..
    Tue Apr 11 15:28:32 2017 - [info] 
    Tue Apr 11 15:28:32 2017 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.
    Tue Apr 11 15:28:32 2017 - [info] Reading application default configuration from /etc/masterha/app1.cnf..
    Tue Apr 11 15:28:32 2017 - [info] Reading server configuration from /etc/masterha/app1.cnf..
    Tue Apr 11 15:28:34 2017 - [info] GTID failover mode = 0
    Tue Apr 11 15:28:34 2017 - [info] Current Alive Master: 192.168.244.10(192.168.244.10:3306)
    Tue Apr 11 15:28:34 2017 - [info] Alive Slaves:
    Tue Apr 11 15:28:34 2017 - [info]   192.168.244.20(192.168.244.20:3306)  Version=5.6.31-log (oldest major version between slaves) log
    -bin:enabledTue Apr 11 15:28:34 2017 - [info]     Replicating from 192.168.244.10(192.168.244.10:3306)
    Tue Apr 11 15:28:34 2017 - [info]     Primary candidate for the new Master (candidate_master is set)
    Tue Apr 11 15:28:34 2017 - [info]   192.168.244.30(192.168.244.30:3306)  Version=5.6.31-log (oldest major version between slaves) log
    -bin:enabledTue Apr 11 15:28:34 2017 - [info]     Replicating from 192.168.244.10(192.168.244.10:3306)
    
    It is better to execute FLUSH NO_WRITE_TO_BINLOG TABLES on the master before switching. Is it ok to execute on 192.168.244.10(192.168
    .244.10:3306)? (YES/no): yes
    Tue Apr 11 15:28:47 2017 - [info] Executing FLUSH NO_WRITE_TO_BINLOG TABLES. This may take long time..
    Tue Apr 11 15:28:47 2017 - [info]  ok.
    Tue Apr 11 15:28:47 2017 - [info] Checking MHA is not monitoring or doing failover..
    Tue Apr 11 15:28:47 2017 - [info] Checking replication health on 192.168.244.20..
    Tue Apr 11 15:28:47 2017 - [info]  ok.
    Tue Apr 11 15:28:47 2017 - [info] Checking replication health on 192.168.244.30..
    Tue Apr 11 15:28:47 2017 - [info]  ok.
    Tue Apr 11 15:28:47 2017 - [info] 192.168.244.20 can be new master.
    Tue Apr 11 15:28:47 2017 - [info] 
    From:
    192.168.244.10(192.168.244.10:3306) (current master)
     +--192.168.244.20(192.168.244.20:3306)
     +--192.168.244.30(192.168.244.30:3306)
    
    To:
    192.168.244.20(192.168.244.20:3306) (new master)
     +--192.168.244.30(192.168.244.30:3306)
     +--192.168.244.10(192.168.244.10:3306)
    
    Starting master switch from 192.168.244.10(192.168.244.10:3306) to 192.168.244.20(192.168.244.20:3306)? (yes/NO): yes
    Tue Apr 11 15:29:00 2017 - [info] Checking whether 192.168.244.20(192.168.244.20:3306) is ok for the new master..
    Tue Apr 11 15:29:00 2017 - [info]  ok.
    Tue Apr 11 15:29:00 2017 - [info] 192.168.244.10(192.168.244.10:3306): SHOW SLAVE STATUS returned empty result. To check replication 
    filtering rules, temporarily executing CHANGE MASTER to a dummy host.Tue Apr 11 15:29:00 2017 - [info] 192.168.244.10(192.168.244.10:3306): Resetting slave pointing to the dummy host.
    Tue Apr 11 15:29:00 2017 - [info] ** Phase 1: Configuration Check Phase completed.
    Tue Apr 11 15:29:00 2017 - [info] 
    Tue Apr 11 15:29:00 2017 - [info] * Phase 2: Rejecting updates Phase..
    Tue Apr 11 15:29:00 2017 - [info] 
    Tue Apr 11 15:29:00 2017 - [info] Executing master ip online change script to disable write on the current master:
    Tue Apr 11 15:29:00 2017 - [info]   /usr/local/bin/master_ip_online_change --command=stop --orig_master_host=192.168.244.10 --orig_ma
    ster_ip=192.168.244.10 --orig_master_port=3306 --orig_master_user='monitor' --orig_master_password='monitor123' --new_master_host=192.168.244.20 --new_master_ip=192.168.244.20 --new_master_port=3306 --new_master_user='monitor' --new_master_password='monitor123' --orig_master_ssh_user=root --new_master_ssh_user=root   --orig_master_is_new_slaveTue Apr 11 15:29:00 2017 476501 Set read_only on the new master.. ok.
    Tue Apr 11 15:29:00 2017 911951 Set read_only=1 on the orig master.. ok.
    Tue Apr 11 15:29:00 2017 919517 Killing all application threads..
    Tue Apr 11 15:29:00 2017 919552 done.
    Disabling the VIP an old master: 192.168.244.10 
    SIOCSIFFLAGS: Cannot assign requested address
    Tue Apr 11 15:29:00 2017 - [info]  ok.
    Tue Apr 11 15:29:00 2017 - [info] Locking all tables on the orig master to reject updates from everybody (including root):
    Tue Apr 11 15:29:00 2017 - [info] Executing FLUSH TABLES WITH READ LOCK..
    Tue Apr 11 15:29:00 2017 - [info]  ok.
    Tue Apr 11 15:29:00 2017 - [info] Orig master binlog:pos is mysql-bin.000016:211.
    Tue Apr 11 15:29:00 2017 - [info]  Waiting to execute all relay logs on 192.168.244.20(192.168.244.20:3306)..
    Tue Apr 11 15:29:01 2017 - [info]  master_pos_wait(mysql-bin.000016:211) completed on 192.168.244.20(192.168.244.20:3306). Executed 0
     events.Tue Apr 11 15:29:01 2017 - [info]   done.
    Tue Apr 11 15:29:01 2017 - [info] Getting new master's binlog name and position..
    Tue Apr 11 15:29:01 2017 - [info]  mysql-bin.000009:211
    Tue Apr 11 15:29:01 2017 - [info]  All other slaves should start replication from here. Statement should be: CHANGE MASTER TO MASTER_
    HOST='192.168.244.20', MASTER_PORT=3306, MASTER_LOG_FILE='mysql-bin.000009', MASTER_LOG_POS=211, MASTER_USER='repl', MASTER_PASSWORD='xxx';Tue Apr 11 15:29:01 2017 - [info] Executing master ip online change script to allow write on the new master:
    Tue Apr 11 15:29:01 2017 - [info]   /usr/local/bin/master_ip_online_change --command=start --orig_master_host=192.168.244.10 --orig_m
    aster_ip=192.168.244.10 --orig_master_port=3306 --orig_master_user='monitor' --orig_master_password='monitor123' --new_master_host=192.168.244.20 --new_master_ip=192.168.244.20 --new_master_port=3306 --new_master_user='monitor' --new_master_password='monitor123' --orig_master_ssh_user=root --new_master_ssh_user=root   --orig_master_is_new_slaveTue Apr 11 15:29:01 2017 109040 Set read_only=0 on the new master.
    Enabling the VIP 192.168.244.188 on the new master: 192.168.244.20 
    Tue Apr 11 15:29:01 2017 - [info]  ok.
    Tue Apr 11 15:29:01 2017 - [info] 
    Tue Apr 11 15:29:01 2017 - [info] * Switching slaves in parallel..
    Tue Apr 11 15:29:01 2017 - [info] 
    Tue Apr 11 15:29:01 2017 - [info] -- Slave switch on host 192.168.244.30(192.168.244.30:3306) started, pid: 17651
    Tue Apr 11 15:29:01 2017 - [info] 
    Tue Apr 11 15:29:02 2017 - [info] Log messages from 192.168.244.30 ...
    Tue Apr 11 15:29:02 2017 - [info] 
    Tue Apr 11 15:29:01 2017 - [info]  Waiting to execute all relay logs on 192.168.244.30(192.168.244.30:3306)..
    Tue Apr 11 15:29:01 2017 - [info]  master_pos_wait(mysql-bin.000016:211) completed on 192.168.244.30(192.168.244.30:3306). Executed 0
     events.Tue Apr 11 15:29:01 2017 - [info]   done.
    Tue Apr 11 15:29:01 2017 - [info]  Resetting slave 192.168.244.30(192.168.244.30:3306) and starting replication from the new master 1
    92.168.244.20(192.168.244.20:3306)..Tue Apr 11 15:29:01 2017 - [info]  Executed CHANGE MASTER.
    Tue Apr 11 15:29:01 2017 - [info]  Slave started.
    Tue Apr 11 15:29:02 2017 - [info] End of log messages from 192.168.244.30 ...
    Tue Apr 11 15:29:02 2017 - [info] 
    Tue Apr 11 15:29:02 2017 - [info] -- Slave switch on host 192.168.244.30(192.168.244.30:3306) succeeded.
    Tue Apr 11 15:29:02 2017 - [info] Unlocking all tables on the orig master:
    Tue Apr 11 15:29:02 2017 - [info] Executing UNLOCK TABLES..
    Tue Apr 11 15:29:02 2017 - [info]  ok.
    Tue Apr 11 15:29:02 2017 - [info] Starting orig master as a new slave..
    Tue Apr 11 15:29:02 2017 - [info]  Resetting slave 192.168.244.10(192.168.244.10:3306) and starting replication from the new master 1
    92.168.244.20(192.168.244.20:3306)..Tue Apr 11 15:29:02 2017 - [info]  Executed CHANGE MASTER.
    Tue Apr 11 15:29:02 2017 - [info]  Slave started.
    Tue Apr 11 15:29:02 2017 - [info] All new slave servers switched successfully.
    Tue Apr 11 15:29:02 2017 - [info] 
    Tue Apr 11 15:29:02 2017 - [info] * Phase 5: New master cleanup phase..
    Tue Apr 11 15:29:02 2017 - [info] 
    Tue Apr 11 15:29:02 2017 - [info]  192.168.244.20: Resetting slave info succeeded.
    Tue Apr 11 15:29:02 2017 - [info] Switching master to 192.168.244.20(192.168.244.20:3306) completed successfully.

![复制代码][48304ba5e6f9fe08f3fa1abda7d326ab.png]

**MHA在线切换的原理**

1. 检查当前的配置信息及主从服务器的信息

包括读取MHA的配置文件/etc/masterha/app1.cnf及检查当前slave的健康状态

2. 阻止对当前master的更新

主要通过如下步骤：

1> 等待1.5s（$time\_until\_kill\_threads\*100ms），等待当前连接断开。

2> 执行 read\_only=1，阻止新的DML操作

3> 等待0.5s，等待当前DML操作完成。

4> kill掉所有连接。

5> FLUSH NO\_WRITE\_TO\_BINLOG TABLES

6> FLUSH TABLES WITH READ LOCK

3. 等待新master执行完所有的relay log

Waiting to execute all relay logs on 192.168.244.20(192.168.244.20:3306)..

4. 将新master的read\_only设置为off，并添加VIP

5. slave切换到新master上。

1> 等待slave（192.168.244.30）应用完原主从复制产生的relay log，然后执行change master操作切换到新master上。

2> 释放原master上加的锁。

3> 因masterha\_master\_switch命令行中带有--orig\_master\_is\_new\_slave参数，故原master也切换为新master的从。

6. 清理新master的相关信息。

主要是执行了reset slave all操作，清除之前的复制信息。

**MHA在线切换需满足的条件**

MHA在执行在线切换之前，会判断当前的主从复制信息，只有满足了以下条件，才能执行切换动作：

1. 所有SLAVE的IO线程和SQL线程都在运行。

2. 所有slave的Seconds\_Behind\_Master小于或等于running\_updates\_limit的值，该参数如果没有显示指定的话，则默认为1s

3. 在master上，通过show processlist输出，没有一个DML操作的时间大于running\_updates\_limit的值。

**在线切换时，打开general log，各个服务器的操作信息**

注：在执行masterha\_master\_switch命令时，会有两次确认操作

1. It is better to execute FLUSH NO\_WRITE\_TO\_BINLOG TABLES on the master before switching. Is it ok to execute on 192.168.244.10(192.168  
.244.10:3306)? (YES/no):

2. Starting master switch from 192.168.244.10(192.168.244.10:3306) to 192.168.244.20(192.168.244.20:3306)? (yes/NO):

以下输出中间都有两次空白，其中第一次空白之前的输出对应第一次确认之前，第二次之前的输出对应第二次确认之前。

**原master 192.168.244.10**

![复制代码][48304ba5e6f9fe08f3fa1abda7d326ab.png]

170412 16:52:38    23 Connect    monitor@node4 on 
                       23 Query    set autocommit=1
                       23 Query    SELECT CONNECTION_ID() AS Value
    170412 16:52:39    24 Connect    monitor@node4 on 
                       24 Query    set autocommit=1
                       24 Query    SELECT CONNECTION_ID() AS Value
                       24 Query    SET wait_timeout=86400
                       24 Query    SELECT @@global.server_id As Value
                       24 Query    SELECT VERSION() AS Value
                       24 Query    SELECT @@global.gtid_mode As Value
                       24 Query    SHOW GLOBAL VARIABLES LIKE 'log_bin'
                       24 Query    SHOW MASTER STATUS
                       24 Query    SELECT @@global.datadir AS Value
                       24 Query    SELECT @@global.slave_parallel_workers AS Value
                       24 Query    SHOW SLAVE STATUS
                       24 Query    SELECT @@global.read_only As Value
                       24 Query    SELECT @@global.relay_log_purge As Value
    
               
    170412 16:54:06    24 Query    FLUSH NO_WRITE_TO_BINLOG TABLES
                       24 Query    SELECT GET_LOCK('MHA_Master_High_Availability_Monitor', '0') AS Value
                       24 Query    SHOW PROCESSLIST
                       
    
    170412 16:55:51    24 Query    SHOW SLAVE STATUS
                       24 Query    CHANGE MASTER TO MASTER_HOST='dummy_host'
    170412 16:55:52    24 Query    SHOW SLAVE STATUS
                       24 Query    RESET SLAVE /*!50516 ALL */
                       24 Query    SELECT RELEASE_LOCK('MHA_Master_High_Availability_Monitor') As Value
                       24 Quit    
                       25 Connect    monitor@node4 on 
                       25 Query    set autocommit=1
                       25 Query    SELECT CONNECTION_ID() AS Value
                       25 Query    SET sql_log_bin=0
                       25 Query    SHOW PROCESSLIST
                       25 Query    SELECT @@global.read_only As Value
                       25 Query    SET GLOBAL read_only=1
                       25 Query    SELECT @@global.read_only As Value
                       25 Query    SHOW PROCESSLIST
                       25 Query    SET sql_log_bin=1
                       25 Quit    
                       26 Connect    monitor@node4 on 
                       26 Query    set autocommit=1
                       26 Query    SELECT CONNECTION_ID() AS Value
                       26 Query    SET wait_timeout=86400
                       26 Query    FLUSH TABLES WITH READ LOCK
                       26 Query    SHOW MASTER STATUS
    170412 16:55:53    26 Query    UNLOCK TABLES
                       26 Query    CHANGE MASTER TO MASTER_HOST = '192.168.244.20' MASTER_USER = 'repl' MASTER_PASSWORD = <secret> MASTE
    R_PORT = 3306 MASTER_LOG_FILE = 'mysql-bin.000010' MASTER_LOG_POS = 120           26 Query    SET GLOBAL relay_log_purge=0
                       26 Query    START SLAVE
                       27 Connect Out    repl@192.168.244.20:3306
                       26 Query    SHOW SLAVE STATUS
                       26 Query    SELECT RELEASE_LOCK('MHA_Master_High_Availability_Failover') As Value
                       26 Quit

![复制代码][48304ba5e6f9fe08f3fa1abda7d326ab.png]

**新master 192.168.244.20**

![复制代码][48304ba5e6f9fe08f3fa1abda7d326ab.png]

170412 16:52:38    23 Connect    monitor@node4 on 
                       23 Query    set autocommit=1
                       23 Query    SELECT CONNECTION_ID() AS Value
    170412 16:52:39    24 Connect    monitor@node4 on 
                       24 Query    set autocommit=1
                       24 Query    SELECT CONNECTION_ID() AS Value
                       24 Query    SET wait_timeout=86400
                       24 Query    SELECT @@global.server_id As Value
                       24 Query    SELECT VERSION() AS Value
                       24 Query    SELECT @@global.gtid_mode As Value
                       24 Query    SHOW GLOBAL VARIABLES LIKE 'log_bin'
                       24 Query    SHOW MASTER STATUS
                       24 Query    SELECT @@global.datadir AS Value
                       24 Query    SELECT @@global.slave_parallel_workers AS Value
                       24 Query    SHOW SLAVE STATUS
                       24 Query    SELECT @@global.read_only As Value
                       24 Query    SELECT @@global.relay_log_purge As Value
                       24 Query    SELECT @@global.relay_log_info_repository AS Value
                       24 Query    SELECT @@global.datadir AS Value
                       24 Query    SELECT @@global.relay_log_info_file AS Value
                       24 Query    SHOW SLAVE STATUS
                       24 Query    SELECT Repl_slave_priv AS Value FROM mysql.user WHERE user = 'repl'
    
               
               
    170412 16:54:06    24 Query    SELECT GET_LOCK('MHA_Master_High_Availability_Failover', '0') AS Value
                       24 Query    SHOW SLAVE STATUS
                       24 Query    SHOW SLAVE STATUS
    
               
    170412 16:55:52    24 Query    SHOW PROCESSLIST
                       25 Connect    monitor@node4 on 
                       25 Query    set autocommit=1
                       25 Query    SELECT CONNECTION_ID() AS Value
                       25 Query    SELECT @@global.read_only As Value
                       25 Query    SELECT @@global.read_only As Value
                       25 Quit    
                       24 Query    SHOW SLAVE STATUS
                       24 Query    SELECT MASTER_POS_WAIT('mysql-bin.000017','120',0) AS Result
                       24 Query    STOP SLAVE SQL_THREAD
                       24 Query    SHOW SLAVE STATUS
                       24 Query    SHOW MASTER STATUS
                       26 Connect    monitor@node4 on 
                       26 Query    set autocommit=1
                       26 Query    SELECT CONNECTION_ID() AS Value
                       26 Query    SET sql_log_bin=0
                       26 Query    SELECT @@global.read_only As Value
                       26 Query    SET GLOBAL read_only=0
                       26 Query    SET sql_log_bin=1
                       26 Quit    
                       24 Query    SELECT @@global.read_only As Value
                       27 Connect    repl@node3 on 
                       27 Query    SELECT UNIX_TIMESTAMP()
                       27 Query    SHOW VARIABLES LIKE 'SERVER_ID'
                       27 Query    SET @master_heartbeat_period= 1799999979520
                       27 Query    SET @master_binlog_checksum= @@global.binlog_checksum
                       27 Query    SELECT @master_binlog_checksum
                       27 Query    SELECT @@GLOBAL.GTID_MODE
                       27 Query    SHOW VARIABLES LIKE 'SERVER_UUID'
                       27 Query    SET @slave_uuid= '8a1093c8-1d00-11e7-954f-000c299a5715'
                       27 Binlog Dump    Log: 'mysql-bin.000010'  Pos: 120
    170412 16:55:53    28 Connect    repl@node1 on 
                       28 Query    SELECT UNIX_TIMESTAMP()
                       28 Query    SHOW VARIABLES LIKE 'SERVER_ID'
                       28 Query    SET @master_heartbeat_period= 1799999979520
                       28 Query    SET @master_binlog_checksum= @@global.binlog_checksum
                       28 Query    SELECT @master_binlog_checksum
                       28 Query    SELECT @@GLOBAL.GTID_MODE
                       28 Query    SHOW VARIABLES LIKE 'SERVER_UUID'
                       24 Query    STOP SLAVE
                       28 Query    SET @slave_uuid= '2a6365e0-1d05-11e7-956d-000c29c64704'
                       28 Binlog Dump    Log: 'mysql-bin.000010'  Pos: 120
                       24 Query    SHOW SLAVE STATUS
                       24 Query    RESET SLAVE /*!50516 ALL */
                       24 Query    SHOW SLAVE STATUS
                       24 Query    SELECT RELEASE_LOCK('MHA_Master_High_Availability_Failover') As Value
                       24 Quit

![复制代码][48304ba5e6f9fe08f3fa1abda7d326ab.png]

**slave 192.168.244.30**

![复制代码][48304ba5e6f9fe08f3fa1abda7d326ab.png]

170412 16:52:37    16 Connect    monitor@node4 on 
                       16 Query    set autocommit=1
                       16 Query    SELECT CONNECTION_ID() AS Value
    170412 16:52:38    17 Connect    monitor@node4 on 
                       17 Query    set autocommit=1
                       17 Query    SELECT CONNECTION_ID() AS Value
                       17 Query    SET wait_timeout=86400
                       17 Query    SELECT @@global.server_id As Value
                       17 Query    SELECT VERSION() AS Value
                       17 Query    SELECT @@global.gtid_mode As Value
                       17 Query    SHOW GLOBAL VARIABLES LIKE 'log_bin'
                       17 Query    SHOW MASTER STATUS
                       17 Query    SELECT @@global.datadir AS Value
                       17 Query    SELECT @@global.slave_parallel_workers AS Value
                       17 Query    SHOW SLAVE STATUS
                       17 Query    SELECT @@global.read_only As Value
                       17 Query    SELECT @@global.relay_log_purge As Value
                       17 Query    SELECT @@global.relay_log_info_repository AS Value
                       17 Query    SELECT @@global.datadir AS Value
                       17 Query    SELECT @@global.relay_log_info_file AS Value
                       17 Query    SHOW SLAVE STATUS
                       17 Query    SELECT Repl_slave_priv AS Value FROM mysql.user WHERE user = 'repl'
    
               
    170412 16:54:05    17 Query    SELECT GET_LOCK('MHA_Master_High_Availability_Failover', '0') AS Value
                       17 Query    SHOW SLAVE STATUS
                       17 Query    SHOW SLAVE STATUS
                       
    
    170412 16:55:50    17 Query    SHOW SLAVE STATUS
    170412 16:55:51    17 Query    SHOW SLAVE STATUS
                       17 Query    SELECT MASTER_POS_WAIT('mysql-bin.000017','120',0) AS Result
                       17 Query    STOP SLAVE SQL_THREAD
                       17 Query    SHOW SLAVE STATUS
                       17 Query    STOP SLAVE
                       17 Query    STOP SLAVE
                       17 Query    SHOW SLAVE STATUS
                       17 Query    RESET SLAVE
                       17 Query    CHANGE MASTER TO MASTER_HOST = '192.168.244.20' MASTER_USER = 'repl' MASTER_PASSWORD = <secret> MASTE
    R_PORT = 3306 MASTER_LOG_FILE = 'mysql-bin.000010' MASTER_LOG_POS = 120           17 Query    SET GLOBAL relay_log_purge=0
                       17 Query    START SLAVE
                       18 Connect Out    repl@192.168.244.20:3306
                       17 Query    SHOW SLAVE STATUS
    170412 16:55:52    17 Query    SELECT RELEASE_LOCK('MHA_Master_High_Availability_Failover') As Value
                       17 Quit

![复制代码][48304ba5e6f9fe08f3fa1abda7d326ab.png]

**参考**

[MySQL_MHA]: http://www.cnblogs.com/ivictor/p/5686275.html
[48304ba5e6f9fe08f3fa1abda7d326ab.png]: /images/20221119/1ef6390049604569b0bb597095af56be.png