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背景:
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 : http://thenoyes.com/littlenoise/?p=117
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
use mysql;<br>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 :
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:
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。
DELIMITER $$DROP PROCEDURE IF EXISTS `mysql`.`rotate_master`$$CREATE DEFINER=`root`@`localhost` PROCEDURE `rotate_master`()BEGINDECLARE _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;SELECTSUBSTRING_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 ', master_user="repl"',<br>', master_password="repl"'<br>);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;ELSEUPDATE mysql.rotate_master SET `repeated_times`=`repeated_times`+1 WHERE in_use = 1;END IF;START SLAVE;END$$DELIMITER ;
创建Event:
每2分钟运行一次,rotate_master() ,即时间片大小是2分钟
DELIMITER $$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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