Mysql Innodb学习经验_MySQL
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Mysql Innodb学习经验
对于数据库来讲大多瓶颈都出现在IO问题上，所以现在SSD类的设备也才能大行其道。那数据库的IO这块有什么可以优化的吗？ 我这里大致谈一下我的看法，希望能达到一个抛砖引玉的效果。
这里谈一下数据库本身的配置方面
具体如下：
配置方面对于IO优化的原则：尽可能能缓存，减少读对数据库的随机IO的请求；同时减少写的随机IO的随时发生，利用各种buffer去缓存。下面来看一下这块的参数：
innodb_buffer_pool_size : 这是Innodb最重要的一个配置参数，这个参数控制Innodb本身的缓大小，也影响到，多少数据能在缓存中。建议该参数的配置在物理内存的70％－80％之间。
innodb_flush_method: 这个控制Innodb的IO形为，什么:fsync, O_DSYNC之类的，这里不做过多介绍， 建议使用: O_DIRECT, 这样减少操作系统级别VFS的缓存使用内存过多和Innodb本身的buffer的缓存冲突，同时也算是给操作系统减少点压力。
innodb_io_capacity: 这个参数据控制Innodb checkpoint时的IO能力，一般可以按一块SAS 15000转的磁盘200个计算，6块盘的SAS做的Raid10这个值可以配到600即可。如果是普通的SATA一块盘只能按100算。(innodb-plugin, Percona有这个参数)
innodb_max_dirty_pages_pct : 这个参数据控制脏页的比例如果是innodb_plugin或是MySQL5.5以上的版本，建议这个参数可以设制到75%-90%都行。如果是大量写入，而且写入的数据不是太活跃，可以考虑把这个值设的低一点。 如果写入或是更新的数据也就是热数据就可以考虑把这个值设为：95%
innodb_log_file_size : 这个可以配置256M以上，建议有两个以前的日志文件(innodb_log_files_in_group). 如果对系统非常大写的情况下，也可以考虑用这个参数提高一下性能，把文件设的大一点，减少checkpiont的发生。 最大可以设制成：innodb_log_files_in_group * innodb_log_file_size innodb_buffer_pool_size/innodb_log_file_in_group 即可。
innodb_log_buffer_size : 如果没在大事务，控制在8M-16M即可。
其它对IO有影响的参数(以5.6为准)
innodb_adaptive_flushing 默认即可
innodb_change_buffer_max_size 如果是日值类服务，可以考虑把这个增值调到 50
innodb_change_buffering 默认即可
innodb_flush_neighors 默认是开的， 这个一定要开着，充分利用顺序IO去写数据。
innodb_lru_scan_depth: 默认即可 这个参数比较专业。
innodb_max_purge_lag 默认没启用，如果写入和读取都量大，可以保证读取优先，可以考虑使用这个功能。
innodb_random_read_ahead 默认没开启，属于一个比较活跃的参数，如果要用一定要多测试一下。 对用passport类应用可以考虑使用
innodb_read_ahead_threshold 默认开启：56 预读机制可以根据业务处理，如果是passprot可以考虑关闭。如果使用innodb_random_read_ahead,建议关闭这个功能
innodb_read_io_threads 默认为：4 可以考虑8
innodb_write_io_threads 默认为：4 可以考虑8
sync_binlog 默认即可： 0
innodb_rollback_segments 默认即可: 128
另外5.6的undo log也可以独立配置了，建议单独配置出来。
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