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HomeDatabaseMysql Tutorial如何使用Percona Toolkit解决Mysql主从不同步问题_MySQL


由于各种原因,mysql主从架构经常会出现数据不一致的情况出现,大致归结为如下几类

  • 1:备库写数据

  • 2:执行non-deterministic query

  • 3:回滚掺杂事务表和非事务表的事务

  • 4:binlog或者relay log数据损坏

数据不同步给应用带来的危害是致命的,当出现主从数据不一致的情况,常见的应对方法是先把从库下线,然后找个半夜三更的时间把应用停掉,重新执行同步,如果数据库的体积十分庞大,那工作量可想而知,会让人崩溃。本文介绍使用percona-toolkit工具对mysql主从数据库的同步状态进行检查和重新同步。

一:安装percona-toolkit

# yum -y install perl-Time-HiRes 
# wget http://www.percona.com/downloads/percona-toolkit/2.2.13/tarball/percona-toolkit-2.2.13.tar.gz 
# tar -zxvpf percona-toolkit-2.2.13.tar.gz 
# cd percona-toolkit-2.2.13 
# perl Makefile.PL 
# make 
# make install

二:修改mysql 的binlog格式binlog_format参数为row格式

mysql binlog日志有三种格式,分别为Statement, Mixed,以及ROW!

1.Statement:

每一条会修改数据的sql都会记录在binlog中。

优点:不需要记录每一行的变化,减少了binlog日志量,节约了IO,提高性能。(相比row能节约多少性能与日志量,这个取决于应用的SQL情况,正常同一条记录修改或者插入row格式所产生的日志量还小于Statement产生的日志量,但是考虑到如果带条件的update操作,以及整表删除,alter表等操作,ROW格式会产生大量日志,因此在考虑是否使用ROW格式日志时应该跟据应用的实际情况,其所产生的日志量会增加多少,以及带来的IO性能问题。)

缺点:由于记录的只是执行语句,为了这些语句能在slave上正确运行,因此还必须记录每条语句在执行的时候的一些相关信息,以保证所有语句能在slave得到和在master端执行时候相同 的结果。另外mysql 的复制,像一些特定函数功能,slave可与master上要保持一致会有很多相关问题(如sleep()函数, last_insert_id(),以及user-defined functions(udf)会出现问题).

2.Row

不记录sql语句上下文相关信息,仅保存哪条记录被修改。

优点: binlog中可以不记录执行的sql语句的上下文相关的信息,仅需要记录那一条记录被修改成什么了。所以rowlevel的日志内容会非常清楚的记录下每一行数据修改的细节。而且不会出现某些特定情况下的存储过程,或function,以及trigger的调用和触发无法被正确复制的问题

缺点:所有的执行的语句当记录到日志中的时候,都将以每行记录的修改来记录,这样可能会产生大量的日志内容,比如一条update语句,修改多条记录,则binlog中每一条修改都会有记录,这样造成binlog日志量会很大,特别是当执行alter table之类的语句的时候,由于表结构修改,每条记录都发生改变,那么该表每一条记录都会记录到日志中。

3.Mixed

是以上两种level的混合使用,一般的语句修改使用statment格式保存binlog,如一些函数,statement无法完成主从复制的操作,则采用row格式保存binlog,MySQL会根据执行的每一条具体的sql语句来区分对待记录的日志形式,也就是在Statement和Row之间选择一种.新版本的MySQL中队row level模式也被做了优化,并不是所有的修改都会以row level来记录,像遇到表结构变更的时候就会以statement模式来记录。至于update或者delete等修改数据的语句,还是会记录所有行的变更。

主从数据库分别修改my.cnf文件相关配置项如下:

<ol class="dp-j list-paddingleft-2"><li><p>binlog_format=ROW <br></p></li></ol>

 以上就是如何使用Percona Toolkit解决Mysql主从不同步问题_MySQL的内容,更多相关内容请关注PHP中文网(www.php.cn)!


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