MHA 在线切换过程

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

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
    ()
    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    :
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)