MySQL MHA 在线切换是MHA除了自动监控切换换提供的另外一种方式，多用于诸如硬件升级，MySQL数据库迁移等等。该方式提供快速切换和优雅的阻塞写入，无关关闭原有服务器，整个切换过程在0.5-2s 的时间左右，大大减少了停机时间。本文演示了MHA 在线切换并给出了在线切换的基本步骤。
1、MHA在线切换方式及要求
$ masterha_master_switch --master_state=alive --conf=/etc/app1.cnf --new_master_host=host2
a、SQL threads on all slaves are running
b、Seconds_Behind_Master on all slaves are less or equal than --running_updates_limit seconds
c、On master, none of update queries take more than --running_updates_limit seconds in the show processlist output
2、在线进行切换基本步骤
a、检测MHA配置置及确认当前master
b、决定新的master
c、阻塞写入到当前master
d、等待所有从服务器与现有master完成同步
e、在新master授予写权限，以及并行切换从库
f、重置原master为新master的slave
3、演示在线切换
###获取masterha_master_switch帮助
[root@vdbsrv4 ~]# masterha_master_switch --help
Usage:
# For master failover
masterha_master_switch --master_state=dead
--global_conf=/etc/masterha_default.cnf
--conf=/usr/local/masterha/conf/app1.cnf --dead_master_host=host1
# For online master switch
masterha_master_switch --master_state=alive
--global_conf=/etc/masterha_default.cnf
--conf=/usr/local/masterha/conf/app1.cnf
See online reference
(http://code.google.com/p/mysql-master-ha/wiki/masterha_master_switch)
for details.
###校验当前是否启用masterha_manager
[root@vdbsrv4 ~]# masterha_check_status --conf=/etc/masterha/app1.cnf
app1 is stopped(2:NOT_RUNNING).
###切换前
mysql> show slave hosts;
+-----------+---------+------+-----------+--------------------------------------+
| Server_id | Host | Port | Master_id | Slave_UUID |
+-----------+---------+------+-----------+--------------------------------------+
| 1001 | vdbsrv2 | 3306 | 1 | 75bef614-e342-11e4-921d-000c295fb2eb |
| 1002 | vdbsrv3 | 3306 | 1 | 091f79b8-e386-11e4-93d5-000c2943c830 |
+-----------+---------+------+-----------+--------------------------------------+
###实施在线切换
[root@vdbsrv4 ~]# masterha_master_switch --conf=/etc/masterha/app1.cnf --master_state=alive --new_master_host=vdbsrv3 \
> --orig_master_is_new_slave --running_updates_limit=10000 --interactive=0
Tue Apr 21 15:42:13 2015 - [info] MHA::MasterRotate version 0.56.
Tue Apr 21 15:42:13 2015 - [info] Starting online master switch..
Tue Apr 21 15:42:13 2015 - [info]
Tue Apr 21 15:42:13 2015 - [info] * Phase 1: Configuration Check Phase..
Tue Apr 21 15:42:13 2015 - [info]
Tue Apr 21 15:42:13 2015 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.
Tue Apr 21 15:42:13 2015 - [info] Reading application default configuration from /etc/masterha/app1.cnf..
Tue Apr 21 15:42:13 2015 - [info] Reading server configuration from /etc/masterha/app1.cnf..
Tue Apr 21 15:42:13 2015 - [info] GTID failover mode = 0
Tue Apr 21 15:42:13 2015 - [info] Current Alive Master: vdbsrv1(192.168.1.6:3306)
Tue Apr 21 15:42:13 2015 - [info] Alive Slaves:
Tue Apr 21 15:42:13 2015 - [info] vdbsrv2(192.168.1.7:3306) Version=5.6.22-log (oldest major version between slaves) log-bin:enabled
Tue Apr 21 15:42:13 2015 - [info] Replicating from 192.168.1.6(192.168.1.6:3306)
Tue Apr 21 15:42:13 2015 - [info] vdbsrv3(192.168.1.8:3306) Version=5.6.22-log (oldest major version between slaves) log-bin:enabled
Tue Apr 21 15:42:13 2015 - [info] Replicating from 192.168.1.6(192.168.1.6:3306)
Tue Apr 21 15:42:13 2015 - [info] Executing FLUSH NO_WRITE_TO_BINLOG TABLES. This may take long time..
Tue Apr 21 15:42:13 2015 - [info] ok.
Tue Apr 21 15:42:13 2015 - [info] Checking MHA is not monitoring or doing failover..
Tue Apr 21 15:42:13 2015 - [info] Checking replication health on vdbsrv2.. ###Author : Leshami
Tue Apr 21 15:42:13 2015 - [info] ok. ###Blog : http://blog.csdn.net/leshami
Tue Apr 21 15:42:13 2015 - [info] Checking replication health on vdbsrv3..
Tue Apr 21 15:42:13 2015 - [info] ok.
Tue Apr 21 15:42:13 2015 - [info] vdbsrv3 can be new master.
Tue Apr 21 15:42:13 2015 - [info]
From:
vdbsrv1(192.168.1.6:3306) (current master)
+--vdbsrv2(192.168.1.7:3306)
+--vdbsrv3(192.168.1.8:3306)
To:
vdbsrv3(192.168.1.8:3306) (new master)
+--vdbsrv2(192.168.1.7:3306)
+--vdbsrv1(192.168.1.6:3306)
Tue Apr 21 15:42:13 2015 - [info] Checking whether vdbsrv3(192.168.1.8:3306) is ok for the new master..
Tue Apr 21 15:42:13 2015 - [info] ok.
Tue Apr 21 15:42:13 2015 - [info] vdbsrv1(192.168.1.6:3306): SHOW SLAVE STATUS returned empty result. To check replication filtering rules,
temporarily executing CHANGE MASTER to a dummy host.
Tue Apr 21 15:42:13 2015 - [info] vdbsrv1(192.168.1.6:3306): Resetting slave pointing to the dummy host.
Tue Apr 21 15:42:13 2015 - [info] ** Phase 1: Configuration Check Phase completed.
Tue Apr 21 15:42:13 2015 - [info]
Tue Apr 21 15:42:13 2015 - [info] * Phase 2: Rejecting updates Phase..
Tue Apr 21 15:42:13 2015 - [info] ###建议部署master_ip_online_change_script 脚本，该脚本会自动阻塞以及kill原master session，置原master为只读
Tue Apr 21 15:42:13 2015 - [warning] master_ip_online_change_script is not defined. Skipping disabling writes on the current master.#此演示未指定
Tue Apr 21 15:42:13 2015 - [info] Locking all tables on the orig master to reject updates from everybody (including root):
Tue Apr 21 15:42:13 2015 - [info] Executing FLUSH TABLES WITH READ LOCK..
Tue Apr 21 15:42:13 2015 - [info] ok.
Tue Apr 21 15:42:13 2015 - [info] Orig master binlog:pos is mysql-bin.000023:651371104.
Tue Apr 21 15:42:13 2015 - [info] Waiting to execute all relay logs on vdbsrv3(192.168.1.8:3306)..
Tue Apr 21 15:42:13 2015 - [info] master_pos_wait(mysql-bin.000023:651371104) completed on vdbsrv3(192.168.1.8:3306). Executed 0 events.
Tue Apr 21 15:42:13 2015 - [info] done.
Tue Apr 21 15:42:13 2015 - [info] Getting new master's binlog name and position..
Tue Apr 21 15:42:13 2015 - [info] mysql-bin.000016:301477519
Tue Apr 21 15:42:13 2015 - [info] All other slaves should start replication from here. Statement should be:
CHANGE MASTER TO MASTER_HOST='vdbsrv3 or 192.168.1.8', MASTER_PORT=3306, MASTER_LOG_FILE='mysql-bin.000016',
MASTER_LOG_POS=301477519, MASTER_USER='repl', MASTER_PASSWORD='xxx';
Tue Apr 21 15:42:13 2015 - [info]
Tue Apr 21 15:42:13 2015 - [info] * Switching slaves in parallel..
Tue Apr 21 15:42:13 2015 - [info]
Tue Apr 21 15:42:13 2015 - [info] -- Slave switch on host vdbsrv2(192.168.1.7:3306) started, pid: 13099
Tue Apr 21 15:42:13 2015 - [info]
Tue Apr 21 15:42:13 2015 - [info] Log messages from vdbsrv2 ...
Tue Apr 21 15:42:13 2015 - [info]
Tue Apr 21 15:42:13 2015 - [info] Waiting to execute all relay logs on vdbsrv2(192.168.1.7:3306)..
Tue Apr 21 15:42:13 2015 - [info] master_pos_wait(mysql-bin.000023:651371104) completed on vdbsrv2(192.168.1.7:3306). Executed 0 events.
Tue Apr 21 15:42:13 2015 - [info] done.
Tue Apr 21 15:42:13 2015 - [info] Resetting slave vdbsrv2(192.168.1.7:3306) and starting replication from the new master vdbsrv3(192.168.1.8:3306)..
Tue Apr 21 15:42:13 2015 - [info] Executed CHANGE MASTER.
Tue Apr 21 15:42:13 2015 - [info] Slave started.
Tue Apr 21 15:42:13 2015 - [info] End of log messages from vdbsrv2 ...
Tue Apr 21 15:42:13 2015 - [info]
Tue Apr 21 15:42:13 2015 - [info] -- Slave switch on host vdbsrv2(192.168.1.7:3306) succeeded.
Tue Apr 21 15:42:13 2015 - [info] Unlocking all tables on the orig master:
Tue Apr 21 15:42:13 2015 - [info] Executing UNLOCK TABLES..
Tue Apr 21 15:42:13 2015 - [info] ok.
Tue Apr 21 15:42:13 2015 - [info] Starting orig master as a new slave..
Tue Apr 21 15:42:13 2015 - [info] Resetting slave vdbsrv1(192.168.1.6:3306) and starting replication from the new master vdbsrv3(192.168.1.8:3306)..
Tue Apr 21 15:42:13 2015 - [info] Executed CHANGE MASTER.
Tue Apr 21 15:42:13 2015 - [info] Slave started.
Tue Apr 21 15:42:13 2015 - [info] All new slave servers switched successfully.
Tue Apr 21 15:42:13 2015 - [info]
Tue Apr 21 15:42:13 2015 - [info] * Phase 5: New master cleanup phase..
Tue Apr 21 15:42:13 2015 - [info]
Tue Apr 21 15:42:13 2015 - [info] vdbsrv3: Resetting slave info succeeded.
Tue Apr 21 15:42:13 2015 - [info] Switching master to vdbsrv3(192.168.1.8:3306) completed successfully.
###切换结果
mysql> show slave hosts;
+-----------+---------+------+-----------+--------------------------------------+
| Server_id | Host | Port | Master_id | Slave_UUID |
+-----------+---------+------+-----------+--------------------------------------+
| 1 | vdbsrv1 | 3306 | 1002 | f2824060-e2cb-11e4-8f18-000c2926f457 |
| 1001 | vdbsrv2 | 3306 | 1002 | 75bef614-e342-11e4-921d-000c295fb2eb |
+-----------+---------+------+-----------+--------------------------------------+