MHA的在线切换后的一些总结（mha方案来自网络）

MHA的在线切换后的一些总结（mha方案来自网络）
mha方案来自：http://www.cnblogs.com/xuanzhi201111/p/4231412.html

MHA的在线切换
192.168.2.131 [root bin]$ masterha_master_switch --conf=/etc/masterha/app1.cnf --master_state=alive --new_master_host=192.168.2.129 --new_master_port=3306 --orig_master_is_new_slave --running_updates_limit=10000
Mon Jan 19 01:51:39 2015 - [info] MHA::MasterRotate version 0.56.
Mon Jan 19 01:51:39 2015 - [info] Starting online master switch..
Mon Jan 19 01:51:39 2015 - [info]
Mon Jan 19 01:51:39 2015 - [info] * Phase 1: Configuration Check Phase..
Mon Jan 19 01:51:39 2015 - [info]
Mon Jan 19 01:51:39 2015 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.
Mon Jan 19 01:51:39 2015 - [info] Reading application default configuration from /etc/masterha/app1.cnf..
Mon Jan 19 01:51:39 2015 - [info] Reading server configuration from /etc/masterha/app1.cnf..
Mon Jan 19 01:51:39 2015 - [info] GTID failover mode = 0
Mon Jan 19 01:51:39 2015 - [info] Current Alive Master: 192.168.2.128(192.168.2.128:3306)
Mon Jan 19 01:51:39 2015 - [info] Alive Slaves:
Mon Jan 19 01:51:39 2015 - [info] 192.168.2.129(192.168.2.129:3306) Version=5.5.30-log (oldest major version between slaves) log-bin:enabled
Mon Jan 19 01:51:39 2015 - [info] Replicating from 192.168.2.128(192.168.2.128:3306)
Mon Jan 19 01:51:39 2015 - [info] Primary candidate for the new Master (candidate_master is set)
Mon Jan 19 01:51:39 2015 - [info] 192.168.2.130(192.168.2.130:3306) Version=5.5.25-log (oldest major version between slaves) log-bin:enabled
Mon Jan 19 01:51:39 2015 - [info] Replicating from 192.168.2.128(192.168.2.128:3306)

It is better to execute FLUSH NO_WRITE_TO_BINLOG TABLES on the master before switching. Is it ok to execute on 192.168.2.128(192.168.2.128:3306)? (YES/no): yes
Mon Jan 19 01:51:46 2015 - [info] Executing FLUSH NO_WRITE_TO_BINLOG TABLES. This may take long time..
Mon Jan 19 01:51:46 2015 - [info] ok.
Mon Jan 19 01:51:46 2015 - [info] Checking MHA is not monitoring or doing failover..
Mon Jan 19 01:51:46 2015 - [info] Checking replication health on 192.168.2.129..
Mon Jan 19 01:51:46 2015 - [info] ok.
Mon Jan 19 01:51:46 2015 - [info] Checking replication health on 192.168.2.130..
Mon Jan 19 01:51:46 2015 - [info] ok.
Mon Jan 19 01:51:46 2015 - [info] 192.168.2.129 can be new master.
Mon Jan 19 01:51:46 2015 - [info]
From:
192.168.2.128(192.168.2.128:3306) (current master)
+--192.168.2.129(192.168.2.129:3306)
+--192.168.2.130(192.168.2.130:3306)

To:
192.168.2.129(192.168.2.129:3306) (new master)
+--192.168.2.130(192.168.2.130:3306)
+--192.168.2.128(192.168.2.128:3306)

Starting master switch from 192.168.2.128(192.168.2.128:3306) to 192.168.2.129(192.168.2.129:3306)? (yes/NO): yes
Mon Jan 19 01:51:50 2015 - [info] Checking whether 192.168.2.129(192.168.2.129:3306) is ok for the new master..
Mon Jan 19 01:51:50 2015 - [info] ok.
Mon Jan 19 01:51:50 2015 - [info] 192.168.2.128(192.168.2.128:3306): SHOW SLAVE STATUS returned empty result. To check replication filtering rules, temporarily executing CHANGE MASTER to a dummy host.
Mon Jan 19 01:51:50 2015 - [info] 192.168.2.128(192.168.2.128:3306): Resetting slave pointing to the dummy host.
Mon Jan 19 01:51:50 2015 - [info] ** Phase 1: Configuration Check Phase completed.
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] * Phase 2: Rejecting updates Phase..
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] Executing master ip online change script to disable write on the current master:
Mon Jan 19 01:51:50 2015 - [info] /usr/local/bin/master_ip_online_change --command=stop --orig_master_host=192.168.2.128 --orig_master_ip=192.168.2.128 --orig_master_port=3306 --orig_master_user='root' --orig_master_password='123456' --new_master_host=192.168.2.129 --new_master_ip=192.168.2.129 --new_master_port=3306 --new_master_user='root' --new_master_password='123456' --orig_master_ssh_user=root --new_master_ssh_user=root --orig_master_is_new_slave
Mon Jan 19 01:51:50 2015 173112 Set read_only on the new master.. ok.
Mon Jan 19 01:51:50 2015 178943 Drpping app user on the orig master..
Mon Jan 19 01:51:50 2015 180438 Set read_only=1 on the orig master.. ok.
Mon Jan 19 01:51:50 2015 183258 Killing all application threads..
Mon Jan 19 01:51:50 2015 183387 done.
Mon Jan 19 01:51:50 2015 - [info] ok.
Mon Jan 19 01:51:50 2015 - [info] Locking all tables on the orig master to reject updates from everybody (including root):
Mon Jan 19 01:51:50 2015 - [info] Executing FLUSH TABLES WITH READ LOCK..
Mon Jan 19 01:51:50 2015 - [info] ok.
Mon Jan 19 01:51:50 2015 - [info] Orig master binlog:pos is mysql-bin.000017:107.
Mon Jan 19 01:51:50 2015 - [info] Waiting to execute all relay logs on 192.168.2.129(192.168.2.129:3306)..
Mon Jan 19 01:51:50 2015 - [info] master_pos_wait(mysql-bin.000017:107) completed on 192.168.2.129(192.168.2.129:3306). Executed 0 events.
Mon Jan 19 01:51:50 2015 - [info] done.
Mon Jan 19 01:51:50 2015 - [info] Getting new master's binlog name and position..
Mon Jan 19 01:51:50 2015 - [info] mysql-bin.000005:61791
Mon Jan 19 01:51:50 2015 - [info] All other slaves should start replication from here. Statement should be: CHANGE MASTER TO MASTER_HOST='192.168.2.129', MASTER_PORT=3306, MASTER_LOG_FILE='mysql-bin.000005', MASTER_LOG_POS=61791, MASTER_USER='repl', MASTER_PASSWORD='xxx';
Mon Jan 19 01:51:50 2015 - [info] Executing master ip online change script to allow write on the new master:
Mon Jan 19 01:51:50 2015 - [info] /usr/local/bin/master_ip_online_change --command=start --orig_master_host=192.168.2.128 --orig_master_ip=192.168.2.128 --orig_master_port=3306 --orig_master_user='root' --orig_master_password='123456' --new_master_host=192.168.2.129 --new_master_ip=192.168.2.129 --new_master_port=3306 --new_master_user='root' --new_master_password='123456' --orig_master_ssh_user=root --new_master_ssh_user=root --orig_master_is_new_slave
Mon Jan 19 01:51:50 2015 443208 Set read_only=0 on the new master.
Mon Jan 19 01:51:50 2015 444741 Creating app user on the new master..
Mon Jan 19 01:51:50 2015 - [info] ok.
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] * Switching slaves in parallel..
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] -- Slave switch on host 192.168.2.130(192.168.2.130:3306) started, pid: 23040
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] Log messages from 192.168.2.130 ...
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] Waiting to execute all relay logs on 192.168.2.130(192.168.2.130:3306)..
Mon Jan 19 01:51:50 2015 - [info] master_pos_wait(mysql-bin.000017:107) completed on 192.168.2.130(192.168.2.130:3306). Executed 0 events.
Mon Jan 19 01:51:50 2015 - [info] done.
Mon Jan 19 01:51:50 2015 - [info] Resetting slave 192.168.2.130(192.168.2.130:3306) and starting replication from the new master 192.168.2.129(192.168.2.129:3306)..
Mon Jan 19 01:51:50 2015 - [info] Executed CHANGE MASTER.
Mon Jan 19 01:51:50 2015 - [info] Slave started.
Mon Jan 19 01:51:50 2015 - [info] End of log messages from 192.168.2.130 ...
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] -- Slave switch on host 192.168.2.130(192.168.2.130:3306) succeeded.
Mon Jan 19 01:51:50 2015 - [info] Unlocking all tables on the orig master:
Mon Jan 19 01:51:50 2015 - [info] Executing UNLOCK TABLES..
Mon Jan 19 01:51:50 2015 - [info] ok.
Mon Jan 19 01:51:50 2015 - [info] Starting orig master as a new slave..
Mon Jan 19 01:51:50 2015 - [info] Resetting slave 192.168.2.128(192.168.2.128:3306) and starting replication from the new master 192.168.2.129(192.168.2.129:3306)..
Mon Jan 19 01:51:50 2015 - [info] Executed CHANGE MASTER.
Mon Jan 19 01:51:50 2015 - [info] Slave started.
Mon Jan 19 01:51:50 2015 - [info] All new slave servers switched successfully.
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] * Phase 5: New master cleanup phase..
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] 192.168.2.129: Resetting slave info succeeded.
Mon Jan 19 01:51:50 2015 - [info] Switching master to 192.168.2.129(192.168.2.129:3306) completed successfully.
192.168.2.131 [root bin]$
192.168.2.131 [root bin]$ masterha_master_switch --conf=/etc/masterha/app1.cnf --master_state=alive --new_master_host=192.168.2.129 --new_master_port=3306 --orig_master_is_new_slave --running_updates_limit=10000 Mon Jan 19 01:51:39 2015 - [info] MHA::MasterRotate version 0.56. Mon Jan 19 01:51:39 2015 - [info] Starting online master switch.. Mon Jan 19 01:51:39 2015 - [info] Mon Jan 19 01:51:39 2015 - [info] * Phase 1: Configuration Check Phase.. Mon Jan 19 01:51:39 2015 - [info] Mon Jan 19 01:51:39 2015 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping. Mon Jan 19 01:51:39 2015 - [info] Reading application default configuration from /etc/masterha/app1.cnf.. Mon Jan 19 01:51:39 2015 - [info] Reading server configuration from /etc/masterha/app1.cnf.. Mon Jan 19 01:51:39 2015 - [info] GTID failover mode = 0 Mon Jan 19 01:51:39 2015 - [info] Current Alive Master: 192.168.2.128(192.168.2.128:3306) Mon Jan 19 01:51:39 2015 - [info] Alive Slaves: Mon Jan 19 01:51:39 2015 - [info] 192.168.2.129(192.168.2.129:3306) Version=5.5.30-log (oldest major version between slaves) log-bin:enabled Mon Jan 19 01:51:39 2015 - [info] Replicating from 192.168.2.128(192.168.2.128:3306) Mon Jan 19 01:51:39 2015 - [info] Primary candidate for the new Master (candidate_master is set) Mon Jan 19 01:51:39 2015 - [info] 192.168.2.130(192.168.2.130:3306) Version=5.5.25-log (oldest major version between slaves) log-bin:enabled Mon Jan 19 01:51:39 2015 - [info] Replicating from 192.168.2.128(192.168.2.128:3306) It is better to execute FLUSH NO_WRITE_TO_BINLOG TABLES on the master before switching. Is it ok to execute on 192.168.2.128(192.168.2.128:3306)? (YES/no): yes Mon Jan 19 01:51:46 2015 - [info] Executing FLUSH NO_WRITE_TO_BINLOG TABLES. This may take long time.. Mon Jan 19 01:51:46 2015 - [info] ok. Mon Jan 19 01:51:46 2015 - [info] Checking MHA is not monitoring or doing failover.. Mon Jan 19 01:51:46 2015 - [info] Checking replication health on 192.168.2.129.. Mon Jan 19 01:51:46 2015 - [info] ok. Mon Jan 19 01:51:46 2015 - [info] Checking replication health on 192.168.2.130.. Mon Jan 19 01:51:46 2015 - [info] ok. Mon Jan 19 01:51:46 2015 - [info] 192.168.2.129 can be new master. Mon Jan 19 01:51:46 2015 - [info] From: 192.168.2.128(192.168.2.128:3306) (current master) +--192.168.2.129(192.168.2.129:3306) +--192.168.2.130(192.168.2.130:3306) To: 192.168.2.129(192.168.2.129:3306) (new master) +--192.168.2.130(192.168.2.130:3306) +--192.168.2.128(192.168.2.128:3306) Starting master switch from 192.168.2.128(192.168.2.128:3306) to 192.168.2.129(192.168.2.129:3306)? (yes/NO): yes Mon Jan 19 01:51:50 2015 - [info] Checking whether 192.168.2.129(192.168.2.129:3306) is ok for the new master.. Mon Jan 19 01:51:50 2015 - [info] ok. Mon Jan 19 01:51:50 2015 - [info] 192.168.2.128(192.168.2.128:3306): SHOW SLAVE STATUS returned empty result. To check replication filtering rules, temporarily executing CHANGE MASTER to a dummy host. Mon Jan 19 01:51:50 2015 - [info] 192.168.2.128(192.168.2.128:3306): Resetting slave pointing to the dummy host. Mon Jan 19 01:51:50 2015 - [info] ** Phase 1: Configuration Check Phase completed. Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] * Phase 2: Rejecting updates Phase.. Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] Executing master ip online change script to disable write on the current master: Mon Jan 19 01:51:50 2015 - [info] /usr/local/bin/master_ip_online_change --command=stop --orig_master_host=192.168.2.128 --orig_master_ip=192.168.2.128 --orig_master_port=3306 --orig_master_user='root' --orig_master_password='123456' --new_master_host=192.168.2.129 --new_master_ip=192.168.2.129 --new_master_port=3306 --new_master_user='root' --new_master_password='123456' --orig_master_ssh_user=root --new_master_ssh_user=root --orig_master_is_new_slave Mon Jan 19 01:51:50 2015 173112 Set read_only on the new master.. ok. Mon Jan 19 01:51:50 2015 178943 Drpping app user on the orig master.. Mon Jan 19 01:51:50 2015 180438 Set read_only=1 on the orig master.. ok. Mon Jan 19 01:51:50 2015 183258 Killing all application threads.. Mon Jan 19 01:51:50 2015 183387 done. Mon Jan 19 01:51:50 2015 - [info] ok. Mon Jan 19 01:51:50 2015 - [info] Locking all tables on the orig master to reject updates from everybody (including root): Mon Jan 19 01:51:50 2015 - [info] Executing FLUSH TABLES WITH READ LOCK.. Mon Jan 19 01:51:50 2015 - [info] ok. Mon Jan 19 01:51:50 2015 - [info] Orig master binlog:pos is mysql-bin.000017:107. Mon Jan 19 01:51:50 2015 - [info] Waiting to execute all relay logs on 192.168.2.129(192.168.2.129:3306).. Mon Jan 19 01:51:50 2015 - [info] master_pos_wait(mysql-bin.000017:107) completed on 192.168.2.129(192.168.2.129:3306). Executed 0 events. Mon Jan 19 01:51:50 2015 - [info] done. Mon Jan 19 01:51:50 2015 - [info] Getting new master's binlog name and position.. Mon Jan 19 01:51:50 2015 - [info] mysql-bin.000005:61791 Mon Jan 19 01:51:50 2015 - [info] All other slaves should start replication from here. Statement should be: CHANGE MASTER TO MASTER_HOST='192.168.2.129', MASTER_PORT=3306, MASTER_LOG_FILE='mysql-bin.000005', MASTER_LOG_POS=61791, MASTER_USER='repl', MASTER_PASSWORD='xxx'; Mon Jan 19 01:51:50 2015 - [info] Executing master ip online change script to allow write on the new master: Mon Jan 19 01:51:50 2015 - [info] /usr/local/bin/master_ip_online_change --command=start --orig_master_host=192.168.2.128 --orig_master_ip=192.168.2.128 --orig_master_port=3306 --orig_master_user='root' --orig_master_password='123456' --new_master_host=192.168.2.129 --new_master_ip=192.168.2.129 --new_master_port=3306 --new_master_user='root' --new_master_password='123456' --orig_master_ssh_user=root --new_master_ssh_user=root --orig_master_is_new_slave Mon Jan 19 01:51:50 2015 443208 Set read_only=0 on the new master. Mon Jan 19 01:51:50 2015 444741 Creating app user on the new master.. Mon Jan 19 01:51:50 2015 - [info] ok. Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] * Switching slaves in parallel.. Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] -- Slave switch on host 192.168.2.130(192.168.2.130:3306) started, pid: 23040 Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] Log messages from 192.168.2.130 ... Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] Waiting to execute all relay logs on 192.168.2.130(192.168.2.130:3306).. Mon Jan 19 01:51:50 2015 - [info] master_pos_wait(mysql-bin.000017:107) completed on 192.168.2.130(192.168.2.130:3306). Executed 0 events. Mon Jan 19 01:51:50 2015 - [info] done. Mon Jan 19 01:51:50 2015 - [info] Resetting slave 192.168.2.130(192.168.2.130:3306) and starting replication from the new master 192.168.2.129(192.168.2.129:3306).. Mon Jan 19 01:51:50 2015 - [info] Executed CHANGE MASTER. Mon Jan 19 01:51:50 2015 - [info] Slave started. Mon Jan 19 01:51:50 2015 - [info] End of log messages from 192.168.2.130 ... Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] -- Slave switch on host 192.168.2.130(192.168.2.130:3306) succeeded. Mon Jan 19 01:51:50 2015 - [info] Unlocking all tables on the orig master: Mon Jan 19 01:51:50 2015 - [info] Executing UNLOCK TABLES.. Mon Jan 19 01:51:50 2015 - [info] ok. Mon Jan 19 01:51:50 2015 - [info] Starting orig master as a new slave.. Mon Jan 19 01:51:50 2015 - [info] Resetting slave 192.168.2.128(192.168.2.128:3306) and starting replication from the new master 192.168.2.129(192.168.2.129:3306).. Mon Jan 19 01:51:50 2015 - [info] Executed CHANGE MASTER. Mon Jan 19 01:51:50 2015 - [info] Slave started. Mon Jan 19 01:51:50 2015 - [info] All new slave servers switched successfully. Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] * Phase 5: New master cleanup phase.. Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] 192.168.2.129: Resetting slave info succeeded. Mon Jan 19 01:51:50 2015 - [info] Switching master to 192.168.2.129(192.168.2.129:3306) completed successfully. 192.168.2.131 [root bin]$
在许多情况下，需要将现有的主服务器迁移到另外一台服务器上。比如主服务器硬件故障，RAID 控制卡需要重建，将主服务器移到性能更好的服务器上等等。维护主服务器引起性能下降，导致停机时间至少无法写入数据。另外，阻塞或杀掉当前运行的会话会导致主主之间数据不一致的问题发生。 MHA 提供快速切换和优雅的阻塞写入，这个切换过程只需要 0.5-2s 的时间，这段时间内数据是无法写入的。在很多情况下，0.5-2s 的阻塞写入是可以接受的。因此切换主服务器不需要计划分配维护时间窗口。

MHA在线切换的大概过程：
（1）检测复制设置和确定当前主服务器
（2）确定新的主服务器
（3）阻塞写入到当前主服务器
（4）等待所有从服务器赶上复制
（5）授予写入到新的主服务器
（6）重新设置从服务器

注意，在线切换的时候应用架构需要考虑以下两个问题：

1.自动识别master和slave的问题（master的机器可能会切换），如果采用了vip的方式，基本可以解决这个问题。

2.负载均衡的问题（可以定义大概的读写比例，每台机器可承担的负载比例，当有机器离开集群时，需要考虑这个问题）

为了保证数据完全一致性，在最快的时间内完成切换，MHA的在线切换必须满足以下条件才会切换成功，否则会切换失败。

(1)所有slave的IO线程都在运行

(2)所有slave的SQL线程都在运行

(3)所有的show slave status的输出中Seconds_Behind_Master参数小于或者等于running_updates_limit秒，如果在切换过程中不指定running_updates_limit,那么默认情况下running_updates_limit为1秒。

(4)在master端，通过show processlist输出，没有一个更新花费的时间大于running_updates_limit秒。

在线切换步骤如下：

在MHA Manager服务器192.168.2.131上操作，首先，停掉MHA监控：
```
192.168.2.131 [root ~]$ masterha_stop --conf=/etc/masterha/app1.cnf
Stopped app1 successfully.
[1]+  Exit 1                  nohup masterha_manager --conf=/etc/masterha/app1.cnf --remove_dead_master_conf --ignore_last_failover < /dev/null > /var/log/masterha/app1/manager.log 2>&1  (wd: /usr/local/bin)
(wd now: ~)
192.168.2.131 [root ~]$ 
```
执行在线切换命令：（以下是0.53版本的manager和node包报的错）
```
Starting master switch from 192.168.2.128(192.168.2.128:3306) to 192.168.2.129(192.168.2.129:3306)? (yes/NO): yes
Sun Jan 18 20:06:17 2015 - [info] Checking whether 192.168.2.129(192.168.2.129:3306) is ok for the new master..
Sun Jan 18 20:06:17 2015 - [info]  ok.
Sun Jan 18 20:06:17 2015 - [info] 192.168.2.128(192.168.2.128:3306): SHOW SLAVE STATUS returned empty result. To check replication filtering rules, temporarily executing CHANGE MASTER to a dummy host.
Sun Jan 18 20:06:17 2015 - [info] 192.168.2.128(192.168.2.128:3306): Resetting slave pointing to the dummy host.
Sun Jan 18 20:06:17 2015 - [info] ** Phase 1: Configuration Check Phase completed.
Sun Jan 18 20:06:17 2015 - [info] 
Sun Jan 18 20:06:17 2015 - [info] * Phase 2: Rejecting updates Phase..
Sun Jan 18 20:06:17 2015 - [info] 
Sun Jan 18 20:06:17 2015 - [info] Executing master ip online change script to disable write on the current master:
Sun Jan 18 20:06:17 2015 - [info]   /usr/local/bin/master_ip_online_change --command=stop --orig_master_host=192.168.2.128 --orig_master_ip=192.168.2.128 --orig_master_port=3306 --new_master_host=192.168.2.129 --new_master_ip=192.168.2.129 --new_master_port=3306  
Got Error: DBI connect(';host=192.168.2.129;port=3306;mysql_connect_timeout=4','',...) failed: Access denied for user 'root'@'192.168.2.131' (using password: NO) at /usr/local/share/perl5/MHA/DBHelper.pm line 181
 at /usr/local/bin/master_ip_online_change line 138

Sun Jan 18 20:06:17 2015 - [error][/usr/local/share/perl5/MHA/ManagerUtil.pm, ln178] Got ERROR:  at /usr/local/bin/masterha_master_switch line 53
```
原因是脚本master_ip_online_change不完整，需要自己进行相应的修改，脚本中new_master_password这个变量获取不到，导致在线切换失败，所以进行了相关的硬编码，直接把mysql的root用户密码赋值给变量new_master_password，但mha4mysql-manager-0.56和mha4mysql-node-0.56版本已经不需要自己把密码直接赋值了，它自己能读出来，之前版本貌似在读new_master_password变量时，总获取不到值（perl脚本我也不太懂，需要大家一起来改善，哈哈）

下面来看来0.56版本的执行情况：
```
192.168.2.131 [root bin]$ masterha_master_switch --conf=/etc/masterha/app1.cnf --master_state=alive --new_master_host=192.168.2.129 --new_master_port=3306  --orig_master_is_new_slave --running_updates_limit=10000
```
192.168.2.131 [root bin]$ masterha_master_switch --conf=/etc/masterha/app1.cnf --master_state=alive --new_master_host=192.168.2.129 --new_master_port=3306 --orig_master_is_new_slave --running_updates_limit=10000
Mon Jan 19 01:51:39 2015 - [info] MHA::MasterRotate version 0.56.
Mon Jan 19 01:51:39 2015 - [info] Starting online master switch..
Mon Jan 19 01:51:39 2015 - [info]
Mon Jan 19 01:51:39 2015 - [info] * Phase 1: Configuration Check Phase..
Mon Jan 19 01:51:39 2015 - [info]
Mon Jan 19 01:51:39 2015 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.
Mon Jan 19 01:51:39 2015 - [info] Reading application default configuration from /etc/masterha/app1.cnf..
Mon Jan 19 01:51:39 2015 - [info] Reading server configuration from /etc/masterha/app1.cnf..
Mon Jan 19 01:51:39 2015 - [info] GTID failover mode = 0
Mon Jan 19 01:51:39 2015 - [info] Current Alive Master: 192.168.2.128(192.168.2.128:3306)
Mon Jan 19 01:51:39 2015 - [info] Alive Slaves:
Mon Jan 19 01:51:39 2015 - [info] 192.168.2.129(192.168.2.129:3306) Version=5.5.30-log (oldest major version between slaves) log-bin:enabled
Mon Jan 19 01:51:39 2015 - [info] Replicating from 192.168.2.128(192.168.2.128:3306)
Mon Jan 19 01:51:39 2015 - [info] Primary candidate for the new Master (candidate_master is set)
Mon Jan 19 01:51:39 2015 - [info] 192.168.2.130(192.168.2.130:3306) Version=5.5.25-log (oldest major version between slaves) log-bin:enabled
Mon Jan 19 01:51:39 2015 - [info] Replicating from 192.168.2.128(192.168.2.128:3306)

It is better to execute FLUSH NO_WRITE_TO_BINLOG TABLES on the master before switching. Is it ok to execute on 192.168.2.128(192.168.2.128:3306)? (YES/no): yes
Mon Jan 19 01:51:46 2015 - [info] Executing FLUSH NO_WRITE_TO_BINLOG TABLES. This may take long time..
Mon Jan 19 01:51:46 2015 - [info] ok.
Mon Jan 19 01:51:46 2015 - [info] Checking MHA is not monitoring or doing failover..
Mon Jan 19 01:51:46 2015 - [info] Checking replication health on 192.168.2.129..
Mon Jan 19 01:51:46 2015 - [info] ok.
Mon Jan 19 01:51:46 2015 - [info] Checking replication health on 192.168.2.130..
Mon Jan 19 01:51:46 2015 - [info] ok.
Mon Jan 19 01:51:46 2015 - [info] 192.168.2.129 can be new master.
Mon Jan 19 01:51:46 2015 - [info]
From:
192.168.2.128(192.168.2.128:3306) (current master)
+--192.168.2.129(192.168.2.129:3306)
+--192.168.2.130(192.168.2.130:3306)

To:
192.168.2.129(192.168.2.129:3306) (new master)
+--192.168.2.130(192.168.2.130:3306)
+--192.168.2.128(192.168.2.128:3306)

Starting master switch from 192.168.2.128(192.168.2.128:3306) to 192.168.2.129(192.168.2.129:3306)? (yes/NO): yes
Mon Jan 19 01:51:50 2015 - [info] Checking whether 192.168.2.129(192.168.2.129:3306) is ok for the new master..
Mon Jan 19 01:51:50 2015 - [info] ok.
Mon Jan 19 01:51:50 2015 - [info] 192.168.2.128(192.168.2.128:3306): SHOW SLAVE STATUS returned empty result. To check replication filtering rules, temporarily executing CHANGE MASTER to a dummy host.
Mon Jan 19 01:51:50 2015 - [info] 192.168.2.128(192.168.2.128:3306): Resetting slave pointing to the dummy host.
Mon Jan 19 01:51:50 2015 - [info] ** Phase 1: Configuration Check Phase completed.
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] * Phase 2: Rejecting updates Phase..
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] Executing master ip online change script to disable write on the current master:
Mon Jan 19 01:51:50 2015 - [info] /usr/local/bin/master_ip_online_change --command=stop --orig_master_host=192.168.2.128 --orig_master_ip=192.168.2.128 --orig_master_port=3306 --orig_master_user='root' --orig_master_password='123456' --new_master_host=192.168.2.129 --new_master_ip=192.168.2.129 --new_master_port=3306 --new_master_user='root' --new_master_password='123456' --orig_master_ssh_user=root --new_master_ssh_user=root --orig_master_is_new_slave
Mon Jan 19 01:51:50 2015 173112 Set read_only on the new master.. ok.
Mon Jan 19 01:51:50 2015 178943 Drpping app user on the orig master..
Mon Jan 19 01:51:50 2015 180438 Set read_only=1 on the orig master.. ok.
Mon Jan 19 01:51:50 2015 183258 Killing all application threads..
Mon Jan 19 01:51:50 2015 183387 done.
Mon Jan 19 01:51:50 2015 - [info] ok.
Mon Jan 19 01:51:50 2015 - [info] Locking all tables on the orig master to reject updates from everybody (including root):
Mon Jan 19 01:51:50 2015 - [info] Executing FLUSH TABLES WITH READ LOCK..
Mon Jan 19 01:51:50 2015 - [info] ok.
Mon Jan 19 01:51:50 2015 - [info] Orig master binlog:pos is mysql-bin.000017:107.
Mon Jan 19 01:51:50 2015 - [info] Waiting to execute all relay logs on 192.168.2.129(192.168.2.129:3306)..
Mon Jan 19 01:51:50 2015 - [info] master_pos_wait(mysql-bin.000017:107) completed on 192.168.2.129(192.168.2.129:3306). Executed 0 events.
Mon Jan 19 01:51:50 2015 - [info] done.
Mon Jan 19 01:51:50 2015 - [info] Getting new master's binlog name and position..
Mon Jan 19 01:51:50 2015 - [info] mysql-bin.000005:61791
Mon Jan 19 01:51:50 2015 - [info] All other slaves should start replication from here. Statement should be: CHANGE MASTER TO MASTER_HOST='192.168.2.129', MASTER_PORT=3306, MASTER_LOG_FILE='mysql-bin.000005', MASTER_LOG_POS=61791, MASTER_USER='repl', MASTER_PASSWORD='xxx';
Mon Jan 19 01:51:50 2015 - [info] Executing master ip online change script to allow write on the new master:
Mon Jan 19 01:51:50 2015 - [info] /usr/local/bin/master_ip_online_change --command=start --orig_master_host=192.168.2.128 --orig_master_ip=192.168.2.128 --orig_master_port=3306 --orig_master_user='root' --orig_master_password='123456' --new_master_host=192.168.2.129 --new_master_ip=192.168.2.129 --new_master_port=3306 --new_master_user='root' --new_master_password='123456' --orig_master_ssh_user=root --new_master_ssh_user=root --orig_master_is_new_slave
Mon Jan 19 01:51:50 2015 443208 Set read_only=0 on the new master.
Mon Jan 19 01:51:50 2015 444741 Creating app user on the new master..
Mon Jan 19 01:51:50 2015 - [info] ok.
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] * Switching slaves in parallel..
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] -- Slave switch on host 192.168.2.130(192.168.2.130:3306) started, pid: 23040
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] Log messages from 192.168.2.130 ...
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] Waiting to execute all relay logs on 192.168.2.130(192.168.2.130:3306)..
Mon Jan 19 01:51:50 2015 - [info] master_pos_wait(mysql-bin.000017:107) completed on 192.168.2.130(192.168.2.130:3306). Executed 0 events.
Mon Jan 19 01:51:50 2015 - [info] done.
Mon Jan 19 01:51:50 2015 - [info] Resetting slave 192.168.2.130(192.168.2.130:3306) and starting replication from the new master 192.168.2.129(192.168.2.129:3306)..
Mon Jan 19 01:51:50 2015 - [info] Executed CHANGE MASTER.
Mon Jan 19 01:51:50 2015 - [info] Slave started.
Mon Jan 19 01:51:50 2015 - [info] End of log messages from 192.168.2.130 ...
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] -- Slave switch on host 192.168.2.130(192.168.2.130:3306) succeeded.
Mon Jan 19 01:51:50 2015 - [info] Unlocking all tables on the orig master:
Mon Jan 19 01:51:50 2015 - [info] Executing UNLOCK TABLES..
Mon Jan 19 01:51:50 2015 - [info] ok.
Mon Jan 19 01:51:50 2015 - [info] Starting orig master as a new slave..
Mon Jan 19 01:51:50 2015 - [info] Resetting slave 192.168.2.128(192.168.2.128:3306) and starting replication from the new master 192.168.2.129(192.168.2.129:3306)..
Mon Jan 19 01:51:50 2015 - [info] Executed CHANGE MASTER.
Mon Jan 19 01:51:50 2015 - [info] Slave started.
Mon Jan 19 01:51:50 2015 - [info] All new slave servers switched successfully.
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] * Phase 5: New master cleanup phase..
Mon Jan 19 01:51:50 2015 - [info]
Mon Jan 19 01:51:50 2015 - [info] 192.168.2.129: Resetting slave info succeeded.
Mon Jan 19 01:51:50 2015 - [info] Switching master to 192.168.2.129(192.168.2.129:3306) completed successfully.
192.168.2.131 [root bin]$
192.168.2.131 [root bin]$ masterha_master_switch --conf=/etc/masterha/app1.cnf --master_state=alive --new_master_host=192.168.2.129 --new_master_port=3306 --orig_master_is_new_slave --running_updates_limit=10000 Mon Jan 19 01:51:39 2015 - [info] MHA::MasterRotate version 0.56. Mon Jan 19 01:51:39 2015 - [info] Starting online master switch.. Mon Jan 19 01:51:39 2015 - [info] Mon Jan 19 01:51:39 2015 - [info] * Phase 1: Configuration Check Phase.. Mon Jan 19 01:51:39 2015 - [info] Mon Jan 19 01:51:39 2015 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping. Mon Jan 19 01:51:39 2015 - [info] Reading application default configuration from /etc/masterha/app1.cnf.. Mon Jan 19 01:51:39 2015 - [info] Reading server configuration from /etc/masterha/app1.cnf.. Mon Jan 19 01:51:39 2015 - [info] GTID failover mode = 0 Mon Jan 19 01:51:39 2015 - [info] Current Alive Master: 192.168.2.128(192.168.2.128:3306) Mon Jan 19 01:51:39 2015 - [info] Alive Slaves: Mon Jan 19 01:51:39 2015 - [info] 192.168.2.129(192.168.2.129:3306) Version=5.5.30-log (oldest major version between slaves) log-bin:enabled Mon Jan 19 01:51:39 2015 - [info] Replicating from 192.168.2.128(192.168.2.128:3306) Mon Jan 19 01:51:39 2015 - [info] Primary candidate for the new Master (candidate_master is set) Mon Jan 19 01:51:39 2015 - [info] 192.168.2.130(192.168.2.130:3306) Version=5.5.25-log (oldest major version between slaves) log-bin:enabled Mon Jan 19 01:51:39 2015 - [info] Replicating from 192.168.2.128(192.168.2.128:3306) It is better to execute FLUSH NO_WRITE_TO_BINLOG TABLES on the master before switching. Is it ok to execute on 192.168.2.128(192.168.2.128:3306)? (YES/no): yes Mon Jan 19 01:51:46 2015 - [info] Executing FLUSH NO_WRITE_TO_BINLOG TABLES. This may take long time.. Mon Jan 19 01:51:46 2015 - [info] ok. Mon Jan 19 01:51:46 2015 - [info] Checking MHA is not monitoring or doing failover.. Mon Jan 19 01:51:46 2015 - [info] Checking replication health on 192.168.2.129.. Mon Jan 19 01:51:46 2015 - [info] ok. Mon Jan 19 01:51:46 2015 - [info] Checking replication health on 192.168.2.130.. Mon Jan 19 01:51:46 2015 - [info] ok. Mon Jan 19 01:51:46 2015 - [info] 192.168.2.129 can be new master. Mon Jan 19 01:51:46 2015 - [info] From: 192.168.2.128(192.168.2.128:3306) (current master) +--192.168.2.129(192.168.2.129:3306) +--192.168.2.130(192.168.2.130:3306) To: 192.168.2.129(192.168.2.129:3306) (new master) +--192.168.2.130(192.168.2.130:3306) +--192.168.2.128(192.168.2.128:3306) Starting master switch from 192.168.2.128(192.168.2.128:3306) to 192.168.2.129(192.168.2.129:3306)? (yes/NO): yes Mon Jan 19 01:51:50 2015 - [info] Checking whether 192.168.2.129(192.168.2.129:3306) is ok for the new master.. Mon Jan 19 01:51:50 2015 - [info] ok. Mon Jan 19 01:51:50 2015 - [info] 192.168.2.128(192.168.2.128:3306): SHOW SLAVE STATUS returned empty result. To check replication filtering rules, temporarily executing CHANGE MASTER to a dummy host. Mon Jan 19 01:51:50 2015 - [info] 192.168.2.128(192.168.2.128:3306): Resetting slave pointing to the dummy host. Mon Jan 19 01:51:50 2015 - [info] ** Phase 1: Configuration Check Phase completed. Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] * Phase 2: Rejecting updates Phase.. Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] Executing master ip online change script to disable write on the current master: Mon Jan 19 01:51:50 2015 - [info] /usr/local/bin/master_ip_online_change --command=stop --orig_master_host=192.168.2.128 --orig_master_ip=192.168.2.128 --orig_master_port=3306 --orig_master_user='root' --orig_master_password='123456' --new_master_host=192.168.2.129 --new_master_ip=192.168.2.129 --new_master_port=3306 --new_master_user='root' --new_master_password='123456' --orig_master_ssh_user=root --new_master_ssh_user=root --orig_master_is_new_slave Mon Jan 19 01:51:50 2015 173112 Set read_only on the new master.. ok. Mon Jan 19 01:51:50 2015 178943 Drpping app user on the orig master.. Mon Jan 19 01:51:50 2015 180438 Set read_only=1 on the orig master.. ok. Mon Jan 19 01:51:50 2015 183258 Killing all application threads.. Mon Jan 19 01:51:50 2015 183387 done. Mon Jan 19 01:51:50 2015 - [info] ok. Mon Jan 19 01:51:50 2015 - [info] Locking all tables on the orig master to reject updates from everybody (including root): Mon Jan 19 01:51:50 2015 - [info] Executing FLUSH TABLES WITH READ LOCK.. Mon Jan 19 01:51:50 2015 - [info] ok. Mon Jan 19 01:51:50 2015 - [info] Orig master binlog:pos is mysql-bin.000017:107. Mon Jan 19 01:51:50 2015 - [info] Waiting to execute all relay logs on 192.168.2.129(192.168.2.129:3306).. Mon Jan 19 01:51:50 2015 - [info] master_pos_wait(mysql-bin.000017:107) completed on 192.168.2.129(192.168.2.129:3306). Executed 0 events. Mon Jan 19 01:51:50 2015 - [info] done. Mon Jan 19 01:51:50 2015 - [info] Getting new master's binlog name and position.. Mon Jan 19 01:51:50 2015 - [info] mysql-bin.000005:61791 Mon Jan 19 01:51:50 2015 - [info] All other slaves should start replication from here. Statement should be: CHANGE MASTER TO MASTER_HOST='192.168.2.129', MASTER_PORT=3306, MASTER_LOG_FILE='mysql-bin.000005', MASTER_LOG_POS=61791, MASTER_USER='repl', MASTER_PASSWORD='xxx'; Mon Jan 19 01:51:50 2015 - [info] Executing master ip online change script to allow write on the new master: Mon Jan 19 01:51:50 2015 - [info] /usr/local/bin/master_ip_online_change --command=start --orig_master_host=192.168.2.128 --orig_master_ip=192.168.2.128 --orig_master_port=3306 --orig_master_user='root' --orig_master_password='123456' --new_master_host=192.168.2.129 --new_master_ip=192.168.2.129 --new_master_port=3306 --new_master_user='root' --new_master_password='123456' --orig_master_ssh_user=root --new_master_ssh_user=root --orig_master_is_new_slave Mon Jan 19 01:51:50 2015 443208 Set read_only=0 on the new master. Mon Jan 19 01:51:50 2015 444741 Creating app user on the new master.. Mon Jan 19 01:51:50 2015 - [info] ok. Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] * Switching slaves in parallel.. Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] -- Slave switch on host 192.168.2.130(192.168.2.130:3306) started, pid: 23040 Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] Log messages from 192.168.2.130 ... Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] Waiting to execute all relay logs on 192.168.2.130(192.168.2.130:3306).. Mon Jan 19 01:51:50 2015 - [info] master_pos_wait(mysql-bin.000017:107) completed on 192.168.2.130(192.168.2.130:3306). Executed 0 events. Mon Jan 19 01:51:50 2015 - [info] done. Mon Jan 19 01:51:50 2015 - [info] Resetting slave 192.168.2.130(192.168.2.130:3306) and starting replication from the new master 192.168.2.129(192.168.2.129:3306).. Mon Jan 19 01:51:50 2015 - [info] Executed CHANGE MASTER. Mon Jan 19 01:51:50 2015 - [info] Slave started. Mon Jan 19 01:51:50 2015 - [info] End of log messages from 192.168.2.130 ... Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] -- Slave switch on host 192.168.2.130(192.168.2.130:3306) succeeded. Mon Jan 19 01:51:50 2015 - [info] Unlocking all tables on the orig master: Mon Jan 19 01:51:50 2015 - [info] Executing UNLOCK TABLES.. Mon Jan 19 01:51:50 2015 - [info] ok. Mon Jan 19 01:51:50 2015 - [info] Starting orig master as a new slave.. Mon Jan 19 01:51:50 2015 - [info] Resetting slave 192.168.2.128(192.168.2.128:3306) and starting replication from the new master 192.168.2.129(192.168.2.129:3306).. Mon Jan 19 01:51:50 2015 - [info] Executed CHANGE MASTER. Mon Jan 19 01:51:50 2015 - [info] Slave started. Mon Jan 19 01:51:50 2015 - [info] All new slave servers switched successfully. Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] * Phase 5: New master cleanup phase.. Mon Jan 19 01:51:50 2015 - [info] Mon Jan 19 01:51:50 2015 - [info] 192.168.2.129: Resetting slave info succeeded. Mon Jan 19 01:51:50 2015 - [info] Switching master to 192.168.2.129(192.168.2.129:3306) completed successfully. 192.168.2.131 [root bin]$
参数说明：
```
--orig_master_is_new_slave 切换时加上此参数是将原 master 变为 slave 节点，如果不加此参数，原来的 master 将不启动

--running_updates_limit=10000,故障切换时,候选master 如果有延迟的话， mha 切换不能成功，加上此参数表示延迟在此时间范围内都可切换（单位为s），但是切换的时间长短是由recover 时relay 日志的大小决定 
```
master_ip_online_change脚本代码如下：

#!/usr/bin/env perl

# Copyright (C) 2011 DeNA Co.,Ltd.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

## Note: This is a sample script and is not complete. Modify the script based on your environment.

use strict;
use warnings FATAL => 'all';

use Getopt::Long;
use MHA::DBHelper;
use MHA::NodeUtil;
use Time::HiRes qw( sleep gettimeofday tv_interval );
use Data::Dumper;

my $_tstart;
my $_running_interval = 0.1;
my (
$command, $orig_master_is_new_slave, $orig_master_host,
$orig_master_ip, $orig_master_port, $orig_master_user,
$orig_master_password, $orig_master_ssh_user, $new_master_host,
$new_master_ip, $new_master_port, $new_master_user,
$new_master_password, $new_master_ssh_user
);
my $vip = '192.168.2.88/24';
my $key = '1';
my $ssh_start_vip = "/sbin/ifconfig eth0:$key $vip";
my $ssh_stop_vip = "/sbin/ifconfig eth0:$key down";
my $orig_master_ssh_port = 22;
my $new_master_ssh_port = 22;
GetOptions(
'command=s' => $command,
'orig_master_is_new_slave' => $orig_master_is_new_slave,
'orig_master_host=s' => $orig_master_host,
'orig_master_ip=s' => $orig_master_ip,
'orig_master_port=i' => $orig_master_port,
'orig_master_user=s' => $orig_master_user,
'orig_master_password=s' => $orig_master_password,
'orig_master_ssh_user=s' => $orig_master_ssh_user,
'new_master_host=s' => $new_master_host,
'new_master_ip=s' => $new_master_ip,
'new_master_port=i' => $new_master_port,
'new_master_user=s' => $new_master_user,
'new_master_password=s' => $new_master_password,
'new_master_ssh_user=s' => $new_master_ssh_user,
'orig_master_ssh_port=i' => $orig_master_ssh_port,
'new_master_ssh_port=i' => $new_master_ssh_port,
);

exit &main();

sub current_time_us {
my ( $sec, $microsec ) = gettimeofday();
my $curdate = localtime($sec);
return $curdate . " " . sprintf( "%06d", $microsec );
}

sub sleep_until {
my $elapsed = tv_interval($_tstart);
if ( $_running_interval > $elapsed ) {
sleep( $_running_interval - $elapsed );
}
}

sub get_threads_util {
my $dbh = shift;
my $my_connection_id = shift;
my $running_time_threshold = shift;
my $type = shift;
$running_time_threshold = 0 unless ($running_time_threshold);
$type = 0 unless ($type);
my @threads;

my $sth = $dbh->prepare("SHOW PROCESSLIST");
$sth->execute();

while ( my $ref = $sth->fetchrow_hashref() ) {
my $id = $ref->{Id};
my $user = $ref->{User};
my $host = $ref->{Host};
my $command = $ref->{Command};
my $state = $ref->{State};
my $query_time = $ref->{Time};
my $info = $ref->{Info};
$info =~ s/^s*(.*?)s*$/$1/ if defined($info);
next if ( $my_connection_id == $id );
next if ( defined($query_time) && $query_time < $running_time_threshold );
next if ( defined($command) && $command eq "Binlog Dump" );
next if ( defined($user) && $user eq "system user" );
next
if ( defined($command)
&& $command eq "Sleep"
&& defined($query_time)
&& $query_time >= 1 );

if ( $type >= 1 ) {
next if ( defined($command) && $command eq "Sleep" );
next if ( defined($command) && $command eq "Connect" );
}

if ( $type >= 2 ) {
next if ( defined($info) && $info =~ m/^select/i );
next if ( defined($info) && $info =~ m/^show/i );
}

push @threads, $ref;
}
return @threads;
}

sub main {
if ( $command eq "stop" ) {
## Gracefully killing connections on the current master
# 1. Set read_only= 1 on the new master
# 2. DROP USER so that no app user can establish new connections
# 3. Set read_only= 1 on the current master
# 4. Kill current queries
# * Any database access failure will result in script die.
my $exit_code = 1;
eval {
## Setting read_only=1 on the new master (to avoid accident)
my $new_master_handler = new MHA::DBHelper();

# args: hostname, port, user, password, raise_error(die_on_error)_or_not
$new_master_handler->connect( $new_master_ip, $new_master_port,
$new_master_user, $new_master_password, 1 );
print current_time_us() . " Set read_only on the new master.. ";
$new_master_handler->enable_read_only();
if ( $new_master_handler->is_read_only() ) {
print "ok. ";
}
else {
die "Failed! ";
}
$new_master_handler->disconnect();

# Connecting to the orig master, die if any database error happens
my $orig_master_handler = new MHA::DBHelper();
$orig_master_handler->connect( $orig_master_ip, $orig_master_port,
$orig_master_user, $orig_master_password, 1 );

## Drop application user so that nobody can connect. Disabling per-session binlog beforehand
$orig_master_handler->disable_log_bin_local();
print current_time_us() . " Drpping app user on the orig master.. ";
#FIXME_xxx_drop_app_user($orig_master_handler);

## Waiting for N * 100 milliseconds so that current connections can exit
my $time_until_read_only = 15;
$_tstart = [gettimeofday];
my @threads = get_threads_util( $orig_master_handler->{dbh},
$orig_master_handler->{connection_id} );
while ( $time_until_read_only > 0 && $#threads >= 0 ) {
if ( $time_until_read_only % 5 == 0 ) {
printf
"%s Waiting all running %d threads are disconnected.. (max %d milliseconds) ",
current_time_us(), $#threads + 1, $time_until_read_only * 100;
if ( $#threads < 5 ) {
print Data::Dumper->new( [$_] )->Indent(0)->Terse(1)->Dump . " "
foreach (@threads);
}
}
sleep_until();
$_tstart = [gettimeofday];
$time_until_read_only--;
@threads = get_threads_util( $orig_master_handler->{dbh},
$orig_master_handler->{connection_id} );
}

## Setting read_only=1 on the current master so that nobody(except SUPER) can write
print current_time_us() . " Set read_only=1 on the orig master.. ";
$orig_master_handler->enable_read_only();
if ( $orig_master_handler->is_read_only() ) {
print "ok. ";
}
else {
die "Failed! ";
}

## Waiting for M * 100 milliseconds so that current update queries can complete
my $time_until_kill_threads = 5;
@threads = get_threads_util( $orig_master_handler->{dbh},
$orig_master_handler->{connection_id} );
while ( $time_until_kill_threads > 0 && $#threads >= 0 ) {
if ( $time_until_kill_threads % 5 == 0 ) {
printf
"%s Waiting all running %d queries are disconnected.. (max %d milliseconds) ",
current_time_us(), $#threads + 1, $time_until_kill_threads * 100;
if ( $#threads < 5 ) {
print Data::Dumper->new( [$_] )->Indent(0)->Terse(1)->Dump . " "
foreach (@threads);
}
}
sleep_until();
$_tstart = [gettimeofday];
$time_until_kill_threads--;
@threads = get_threads_util( $orig_master_handler->{dbh},
$orig_master_handler->{connection_id} );
}

## Terminating all threads
print current_time_us() . " Killing all application threads.. ";
$orig_master_handler->kill_threads(@threads) if ( $#threads >= 0 );
print current_time_us() . " done. ";
$orig_master_handler->enable_log_bin_local();
$orig_master_handler->disconnect();

## After finishing the script, MHA executes FLUSH TABLES WITH READ LOCK
eval {
`ssh -p$orig_master_ssh_port $orig_master_ssh_user@$orig_master_host " $ssh_stop_vip "`;
};
if ($@) {
warn $@;
}
$exit_code = 0;
};
if ($@) {
warn "Got Error: $@ ";
exit $exit_code;
}
exit $exit_code;
}
elsif ( $command eq "start" ) {
## Activating master ip on the new master
# 1. Create app user with write privileges
# 2. Moving backup script if needed
# 3. Register new master's ip to the catalog database

# We don't return error even though activating updatable accounts/ip failed so that we don't interrupt slaves' recovery.
# If exit code is 0 or 10, MHA does not abort
my $exit_code = 10;
eval {
my $new_master_handler = new MHA::DBHelper();

# args: hostname, port, user, password, raise_error_or_not
$new_master_handler->connect( $new_master_ip, $new_master_port,
$new_master_user, $new_master_password, 1 );

## Set read_only=0 on the new master
$new_master_handler->disable_log_bin_local();
print current_time_us() . " Set read_only=0 on the new master. ";
$new_master_handler->disable_read_only();

## Creating an app user on the new master
print current_time_us() . " Creating app user on the new master.. ";
#FIXME_xxx_create_app_user($new_master_handler);
$new_master_handler->enable_log_bin_local();
$new_master_handler->disconnect();

## Update master ip on the catalog database, etc
`ssh -p$new_master_ssh_port $new_master_ssh_user@$new_master_host " $ssh_start_vip "`;
$exit_code = 0;
};
if ($@) {
warn "Got Error: $@ ";
exit $exit_code;
}
exit $exit_code;
}
elsif ( $command eq "status" ) {

# do nothing
exit 0;
}
else {
&usage();
exit 1;
}
}

sub usage {
print
"Usage: master_ip_online_change --command=start|stop|status --orig_master_host=host --orig_master_ip=ip --orig_master_port=port --new_master_host=host --new_master_ip=ip --new_master_port=port ";
die;
}

说明可以参考官网：https://code.google.com/p/mysql-master-ha/wiki/Parameters#master_ip_online_change_script（自备梯子）

2、修复宕机的Master

通常情况下自动切换以后，原master可能已经废弃掉，待原master主机修复后，如果数据完整的情况下，可能想把原来master重新作为新主库的slave，这时我们可以借助当时自动切换时刻的MHA日志来完成对原master的修复。下面是提取相关日志的命令：

从上面信息可以看到：
```
All other slaves should start replication from here. Statement should be: CHANGE MASTER TO MASTER_HOST='192.168.2.129', MASTER_PORT=3306, MASTER_LOG_FILE='mysql-bin.000005', MASTER_LOG_POS=61791, MASTER_USER='repl', MASTER_PASSWORD='xxx';
```
意思是说，如果Master主机修复好了，可以在修复好后的Master执行CHANGE MASTER操作，作为新的slave库。

目前高可用方案可以一定程度上实现数据库的高可用，比如前面文章介绍的MMM，heartbeat+drbd，Cluster等。还有percona的Galera Cluster等。这些高可用软件各有优劣。在进行高可用方案选择时，主要是看业务还有对数据一致性方面的要求。最后出于对数据库的高可用和数据一致性的要求，推荐使用MHA架构。

总结：

1.mha manager没有运行

2.集群运行正常

3.执行切换后old master变成第二master，与原第二master互换角色（在数据了很小情况下测试得出的，并且主备是同步的，这种切换对主备同步有要求，不能差距太多）

4.还可以执行同样操作，再次切换角色
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原文地址：https://www.cnblogs.com/lixigang/p/5133320.html