MySQL Multi-Master实现方式

MySQL Mutil-Master Replication喊了很久了，但是MySQL一直没有去，虽然在MySQL源码中有注释将实现Multi-Master，mi结构体也为Multi-Master做好了准备，但是却一直不见MySQL发布。

但是Multi-Master –> Slave的Repliction确实非常有用，例如一台集中备份机备份所有Master的数据。

实现Multi-Master有几种思路：
1. 修改MySQL源码：修改sql_yacc.yy, sql_lex.cc支持多Master的CHANGE MASTER TO语法，然后修改slave相关的slave.cc，支持开启多个Slave, 将slave io/ slave thread线程扩展为一个slave_list。
2. 利用mysqlbinlog之类的工具，远程注册到Master获取binlog，导入本地Slave服务器。

从效率看，肯定第一种方式效率高，但是风险太大了，并且MySQL版本更新，可能需要变动自己的代码以适应新的MySQL Source, MySQL官方的实现方式肯定是第一种，从源码中的注释可以看出他们的设计思路。但是他们考虑的问题可能是多个Master复制如何处理冲突等异常，因而迟迟不发布。

为了避免过多的入侵MySQL，我采用第二种方式，用一个脚本或者程序等等，去调用mysqlbinlog，用-R远程请求到–to-last-log，然后稍微修改一下啊mysqlbinlog的源码，在日志切换后计数一下，在输出文件末尾打上切换日志的个数，例如：

insert into a values (8)/*!*/;
# at 1070#110114 16:16:11 server id 3  end_log_pos 1097 	Xid = 36COMMIT/*!*/;
DELIMITER ;
# End of log file
ROLLBACK /* added by mysqlbinlog */;/*!50003 SET COMPLETION_TYPE=@OLD_COMPLETION_TYPE*/;-- Rorate binlog count: 1

— Rorate binlog count: 1就是日志切换信息，表示切换了一次日志（即传入Master的日志号没有用完）然后tail末尾的end_pos来查看本次同步到哪里了，写到*.info的文件中。

我的脚本需要配置一个multi_master.conf文件，配好每个Master的信息，例如：

#cat multi_master.conf 
[master1]MASTER_HOST=1.2.3.4
MASTER_USER=plx
MASTER_PASSWORD=plx
MASTER_PORT=3306MASTER_LOG_NAME=mysql-bin
MASTER_LOG_IDX=000002
MASTER_LOG_POS=521RELAY_LOG_DIR=/tmp/RELAY_LOG_NAME=1-relay-bin
 [master2]MASTER_HOST=2.3.4.5
MASTER_USER=plx
MASTER_PASSWORD=plx
MASTER_PORT=3306MASTER_LOG_NAME=mysql-bin
MASTER_LOG_IDX=000002
MASTER_LOG_POS=581RELAY_LOG_DIR=/tmp/RELAY_LOG_NAME=2-relay-bin
 [slave]SLAVE_USER=plx
SLAVE_PASSWORD=plx

SLAVE默认导入本地，所以没有提供主机选项。
配置文件的含义是，定义了master1和master2两个Master，名称其实只要不是slave都行，[slave]中定义了本地导入的用户名和密码。
特有的参数我解释下，没解释的跟MySQL一样，
MASTER_LOG_NAME和MASTER_LOG_IDX组成MySQL中的Master_log_file，RELAY_LOG_DIR表示取回的binlog文件放哪个目录，RELAY_LOG_NAME是Relay文件的文件名，会加上标号，跟MySQL一样，这个脚本会自动处理。
一旦执行过一次，就会生成master1.info之类的文件，来表示当前同步到哪里了，例如下面这个例子：

MASTER_LOG_POS=1482NAME=master1
MASTER_USER=plx
RELAY_LOG_NAME=1-relay-bin
MASTER_LOG_IDX=2MASTER_HOST=1.2.3.4
MASTER_LOG_NAME=mysql-bin
MASTER_PORT=3306RELAY_LOG_DIR=/tmp/MASTER_PASSWORD=plx
RELAY_LOG_IDX=3

只有找不到*.info的时候，才会使用multi_master.conf。

现在每次调度multi_master_repl.pl都只会运行一次，可以不断的调度multi_master_repl.pl，因为还没有完全搞定KILL信号在Perl脚本的处理，用C重写后会解决，不能暴力kill -9，会导致不知道复制到哪里了。

这是下载地址，切勿用在生产环境，这只是个验证想法的程序。

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下一步我想用C重新实现，在mysqlbinlog源码基础上修改，获取到的日志直接写入到sock或直接导入远程mysql，避免多写一次文件，也欢迎提供新思路。

这是一次执行的日志：

#./multi_master_repl.pl 
(DEBUG) Enter: get_config()
	Info: begin
	(DEBUG) get_config --> master1
	(DEBUG) get_config --> multi_master.conf --> master1:MASTER_HOST=1.2.3.4
	(DEBUG) get_config --> multi_master.conf --> master1:MASTER_USER=plx
	(DEBUG) get_config --> multi_master.conf --> master1:MASTER_PASSWORD=plx
	(DEBUG) get_config --> multi_master.conf --> master1:MASTER_PORT=3306
	(DEBUG) get_config --> multi_master.conf --> master1:MASTER_LOG_NAME=mysql-bin
	(DEBUG) get_config --> multi_master.conf --> master1:MASTER_LOG_IDX=000002
	(DEBUG) get_config --> multi_master.conf --> master1:MASTER_LOG_POS=521
	(DEBUG) get_config --> multi_master.conf --> master1:RELAY_LOG_DIR=/tmp/
	(DEBUG) get_config --> multi_master.conf --> master1:RELAY_LOG_NAME=1-relay-bin
	(DEBUG) get_config --> Found master1.info, Read it
	(DEBUG) get_config --> master1.info --> master1:MASTER_LOG_POS=1097
	(DEBUG) get_config --> master1.info --> master1:NAME=master1
	(DEBUG) get_config --> master1.info --> master1:MASTER_USER=plx
	(DEBUG) get_config --> master1.info --> master1:RELAY_LOG_NAME=1-relay-bin
	(DEBUG) get_config --> master1.info --> master1:MASTER_LOG_IDX=2
	(DEBUG) get_config --> master1.info --> master1:MASTER_HOST=1.2.3.4
	(DEBUG) get_config --> master1.info --> master1:MASTER_LOG_NAME=mysql-bin
	(DEBUG) get_config --> master1.info --> master1:MASTER_PORT=3306
	(DEBUG) get_config --> master1.info --> master1:RELAY_LOG_DIR=/tmp/
	(DEBUG) get_config --> master1.info --> master1:MASTER_PASSWORD=plx
	(DEBUG) get_config --> master1.info --> master1:RELAY_LOG_IDX=2
	(DEBUG) get_config --> Push[master1] to Master_Info_List
	(DEBUG) get_config --> master2
	(DEBUG) get_config --> multi_master.conf --> master2:MASTER_HOST=2.3.4.5
	(DEBUG) get_config --> multi_master.conf --> master2:MASTER_USER=plx
	(DEBUG) get_config --> multi_master.conf --> master2:MASTER_PASSWORD=plx
	(DEBUG) get_config --> multi_master.conf --> master2:MASTER_PORT=3306
	(DEBUG) get_config --> multi_master.conf --> master2:MASTER_LOG_NAME=mysql-bin
	(DEBUG) get_config --> multi_master.conf --> master2:MASTER_LOG_IDX=000002
	(DEBUG) get_config --> multi_master.conf --> master2:MASTER_LOG_POS=581
	(DEBUG) get_config --> multi_master.conf --> master2:RELAY_LOG_DIR=/tmp/
	(DEBUG) get_config --> multi_master.conf --> master2:RELAY_LOG_NAME=2-relay-bin
	(DEBUG) get_config --> Found master2.info, Read it
	(DEBUG) get_config --> master2.info --> master2:MASTER_LOG_POS=1541
	(DEBUG) get_config --> master2.info --> master2:NAME=master2
	(DEBUG) get_config --> master2.info --> master2:MASTER_USER=plx
	(DEBUG) get_config --> master2.info --> master2:RELAY_LOG_NAME=2-relay-bin
	(DEBUG) get_config --> master2.info --> master2:MASTER_LOG_IDX=2
	(DEBUG) get_config --> master2.info --> master2:MASTER_HOST=2.3.4.5
	(DEBUG) get_config --> master2.info --> master2:MASTER_LOG_NAME=mysql-bin
	(DEBUG) get_config --> master2.info --> master2:MASTER_PORT=3306
	(DEBUG) get_config --> master2.info --> master2:RELAY_LOG_DIR=/tmp/
	(DEBUG) get_config --> master2.info --> master2:MASTER_PASSWORD=plx
	(DEBUG) get_config --> master2.info --> master2:RELAY_LOG_IDX=2
	(DEBUG) get_config --> Push[master2] to Master_Info_List
	(DEBUG) get_config --> multi_master.conf --> slave:SLAVE_USER=plx
	(DEBUG) get_config --> multi_master.conf --> slave:SLAVE_PASSWORD=plx
(DEBUG) Enter: get_config()
	Info: exit
(DEBUG) Enter: create_slave_threads()
	Info: begin
	(DEBUG) create_slave_threads --> Creating run_slave Threads...
(DEBUG) Enter: run_slave()
	Info: begin [tid: 1]
	(DEBUG) run_slave(0) --> NO KILL SIGNAL --> g_is_killed =>0
	(DEBUG) run_slave --> mysqlbinlog: ./mysqlbinlog -h1.2.3.4 -uplx -pplx -R -t --start-position=1097 mysql-bin.000002 > /tmp/1-relay-bin.000002
Warning: ./mysqlbinlog: unknown variable 'loose_default-character-set=utf8'
	(DEBUG) run_slave(0) --> NO KILL SIGNAL --> g_is_killed =>0
(DEBUG) Enter: import_to_slave()
	Info: begin [Param: p_master_idx=>0]
	(DEBUG) import_to_slave(0) --> NO KILL SIGNAL --> g_is_killed =>0
	(DEBUG) import_to_slave(0) --> Importing Relay Log /tmp/1-relay-bin.000002 To Slave...
	(DEBUG) create_slave_threads --> Created 2 run_slave Threads
(DEBUG) Enter: run_slave()
	Info: begin [tid: 2]
	(DEBUG) run_slave(1) --> NO KILL SIGNAL --> g_is_killed =>0
	(DEBUG) run_slave --> mysqlbinlog: ./mysqlbinlog -h2.3.4.5 -uplx -pplx -R -t --start-position=1541 mysql-bin.000002 > /tmp/2-relay-bin.000002
Warning: ./mysqlbinlog: unknown variable 'loose_default-character-set=utf8'
	(DEBUG) run_slave(1) --> NO KILL SIGNAL --> g_is_killed =>0
(DEBUG) Enter: import_to_slave()
	Info: begin [Param: p_master_idx=>1]
	(DEBUG) import_to_slave(1) --> NO KILL SIGNAL --> g_is_killed =>0
	(DEBUG) import_to_slave(1) --> Importing Relay Log /tmp/2-relay-bin.000002 To Slave...
(DEBUG) Enter: update_master_info()
	Info: begin [Param: p_master_idx=>0]
(DEBUG) Enter: update_master_info()
	Info: begin [Param: p_master_idx=>1]
	(DEBUG) update_master_info(0) --> Now Master-Log is mysql-bin.000002 Pos is 1482
(DEBUG) Enter: update_master_info_file()
	Info: begin [Param: p_master_idx=>0]
	(DEBUG) update_master_info_file(0) --> NO KILL SIGNAL --> g_is_killed =>0
	(DEBUG) update_master_info_file(0) --> Writing master1.info --> MASTER_LOG_POS=1482
	(DEBUG) update_master_info_file(0) --> Writing master1.info --> NAME=master1
	(DEBUG) update_master_info_file(0) --> Writing master1.info --> MASTER_USER=plx
	(DEBUG) update_master_info_file(0) --> Writing master1.info --> RELAY_LOG_NAME=1-relay-bin
	(DEBUG) update_master_info_file(0) --> Writing master1.info --> MASTER_LOG_IDX=2
	(DEBUG) update_master_info_file(0) --> Writing master1.info --> MASTER_HOST=1.2.3.4
	(DEBUG) update_master_info_file(0) --> Writing master1.info --> MASTER_LOG_NAME=mysql-bin
	(DEBUG) update_master_info_file(0) --> Writing master1.info --> MASTER_PORT=3306
	(DEBUG) update_master_info_file(0) --> Writing master1.info --> RELAY_LOG_DIR=/tmp/
	(DEBUG) update_master_info_file(0) --> Writing master1.info --> MASTER_PASSWORD=plx
	(DEBUG) update_master_info_file(0) --> Writing master1.info --> RELAY_LOG_IDX=3
	(DEBUG) update_master_info_file(0) --> Created master1.info
(DEBUG) Enter: update_master_info_file(0)
	Info: exit
(DEBUG) Enter: update_master_info(0)
	Info: exit
(DEBUG) Enter: import_to_slave(0)
	Info: exit
(DEBUG) Enter: run_slave(0)
	Info: exit
	(DEBUG) update_master_info(1) --> Now Master-Log is mysql-bin.000002 Pos is 2120
(DEBUG) Enter: update_master_info_file()
	Info: begin [Param: p_master_idx=>1]
	(DEBUG) update_master_info_file(1) --> NO KILL SIGNAL --> g_is_killed =>0
	(DEBUG) update_master_info_file(1) --> Writing master2.info --> MASTER_LOG_POS=2120
	(DEBUG) update_master_info_file(1) --> Writing master2.info --> NAME=master2
	(DEBUG) update_master_info_file(1) --> Writing master2.info --> MASTER_USER=plx
	(DEBUG) update_master_info_file(1) --> Writing master2.info --> RELAY_LOG_NAME=2-relay-bin
	(DEBUG) update_master_info_file(1) --> Writing master2.info --> MASTER_LOG_IDX=2
	(DEBUG) update_master_info_file(1) --> Writing master2.info --> MASTER_HOST=2.3.4.5
	(DEBUG) update_master_info_file(1) --> Writing master2.info --> MASTER_LOG_NAME=mysql-bin
	(DEBUG) update_master_info_file(1) --> Writing master2.info --> MASTER_PORT=3306
	(DEBUG) update_master_info_file(1) --> Writing master2.info --> RELAY_LOG_DIR=/tmp/
	(DEBUG) update_master_info_file(1) --> Writing master2.info --> MASTER_PASSWORD=plx
	(DEBUG) update_master_info_file(1) --> Writing master2.info --> RELAY_LOG_IDX=3
	(DEBUG) update_master_info_file(1) --> Created master2.info
(DEBUG) Enter: update_master_info_file(1)
	Info: exit
(DEBUG) Enter: update_master_info(1)
	Info: exit
(DEBUG) Enter: import_to_slave(1)
	Info: exit
(DEBUG) Enter: run_slave(1)
	Info: exit
(DEBUG) Enter: create_slave_threads()
	Info: exit