使用Rotate Master实现MySQL 多主复制的实现方法
众所周知,MySQL只支持一对多的主从复制,而不支持多主(multi-master)复制
当然,5.6的GUID功能的出现也带来了multi-master的无限可能,不过这个已经是题外话了。本文主要介绍一种非实时的适用于各版本MySQL的multi-master方法。
内容简介:
最初的思路来源于一位国外DBA的blog :
基本原理就是通过SP记录当前 master-log的name和pos记录到表中,然后读取下一个master记录,执行stop slave / change master / start slave。以此循环反复。
个人对他的方法进行了改进,增加了以下功能:
1. master可以根据业务流量设置权重值
2. 各个master-slave运行情况的监控
3. 各个master可以实时退出多主的架构
具体操作过程:
1. 创建保存各个master信息的表
代码如下:
use mysql;
CREATE TABLE `rotate_master` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`master_host` varchar(255) DEFAULT NULL comment 'master地址',
`master_port` int(10) unsigned DEFAULT NULL comment 'master端口' ,
`master_log_file` varchar(255) DEFAULT NULL ‘上次停止时的master-log文件',
`master_log_pos` int(10) unsigned DEFAULT NULL comment '上次停止时的master-log-pos',
`IS_Slave_Running` varchar(10) DEFAULT NULL comment '上次停止时主从是否有异常',
`in_use` tinyint(1) DEFAULT '0' comment '是否是当前正在同步的数据行',
`weight` int(11) NOT NULL DEFAULT '1' comment '该master的权重,即重复执行多少个时间片',
`repeated_times` int(11) NOT NULL DEFAULT '0' comment '当前已经重复执行的时间片数',
`LastExecuteTime` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP comment '上次执行的时间',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
新增加一个master :
代码如下:
insert into `rotate_master`
(`master_host`,`master_port`,`master_log_file`,`master_log_pos`,`in_use`,`weight`)
values
-- 1号master,权重=1,并设置为当前master
('192.168.0.1',3307,'mysqlbinlog.000542',4,1,1),
-- 2号master,权重=2
('192.168.0.2',3306,'mysqlbinlog.000702',64762429,0,2),
-- 3号master,权重=5
('192.168.0.3',3306,'mysqlbinlog.000646',22157422,0,5)
手工把master 调整到当前的配置项:
代码如下:
change master to master_host='192.168.0.1', master_port=3306,master_log_file='mysqlbinlog.000542',master_log_pos=4,master_user='repl',master_password='repl';
start slave;
创建rotate master SP:
注意:代码中用于连接master的用户名和密码是 : repl / repl ,请根据自己的情况修改。
代码如下:
DELIMITER $$
DROP PROCEDURE IF EXISTS `mysql`.`rotate_master`$$
CREATE DEFINER=`root`@`localhost` PROCEDURE `rotate_master`()
BEGIN
DECLARE _info text;
DECLARE _master_file varchar(255);
DECLARE _master_pos int unsigned;
DECLARE _master_host varchar(255);
DECLARE _master_port int unsigned;
DECLARE _is_slave_running varchar(10);
DECLARE _id int;
DECLARE _weight int;
DECLARE _repeated_times int;
select VARIABLE_VALUE from information_schema.GLOBAL_STATUS where VARIABLE_NAME = 'Slave_running' into _is_slave_running;
STOP SLAVE;
SELECT LOAD_FILE(@@relay_log_info_file) INTO _info;
SELECT
SUBSTRING_INDEX(SUBSTRING_INDEX(_info, '\n', 3), '\n', -1),
SUBSTRING_INDEX(SUBSTRING_INDEX(_info, '\n', 4), '\n', -1)
INTO _master_file, _master_pos;
UPDATE mysql.rotate_master SET `master_log_file` = _master_file, `master_log_pos` = _master_pos, id = LAST_INSERT_ID(id), `IS_Slave_Running` = _is_slave_running WHERE in_use = 1;
select weight,repeated_times into _weight,_repeated_times from mysql.rotate_master where in_use =1;
if(_weight THEN
SELECT
id,
master_host,
master_port,
master_log_file,
master_log_pos
INTO _id, _master_host, _master_port, _master_file, _master_pos
FROM rotate_master
ORDER BY id SET @sql := CONCAT(
'CHANGE MASTER TO master_host=', QUOTE(_master_host),
', master_port=', _master_port,
', master_log_file=', QUOTE(_master_file),
', master_log_pos=', _master_pos
', master_user="repl"',
', master_password="repl"'
);
PREPARE myStmt FROM @sql;
EXECUTE myStmt;
UPDATE mysql.rotate_master SET in_use = 0,repeated_times=0 WHERE in_use = 1;
UPDATE mysql.rotate_master SET in_use = 1,repeated_times=1 WHERE id = _id;
ELSE
UPDATE mysql.rotate_master SET `repeated_times`=`repeated_times`+1 WHERE in_use = 1;
END IF;
START SLAVE;
END$$
DELIMITER ;
创建Event:
每2分钟运行一次,rotate_master() ,即时间片大小是2分钟
代码如下:
DELIMITER $$
CREATE EVENT `rotate_master` ON SCHEDULE EVERY 120 SECOND STARTS '2011-10-13 14:09:40' ON COMPLETION NOT PRESERVE ENABLE DO CALL mysql.rotate_master()$$
DELIMITER ;
至此,多主复制已经搭建完成。
由于时间片长度是2分钟。
Master1 在执行 1*2 分钟后,stop slave,然后change master to Master2;
Master2 在执行 2*2 分钟后,stop slave,然后change master to Master3;
Master3 在执行 5*2 分钟后,stop slave,然后change master to Master2;
并以此循环往复。
如果希望把其中一个master移除多主复制,可以将他的配置项权重设置为0;
即: update rotate_master set weigh=0 where id = #ID# ;

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