MySQL优化三(InnoDB优化)

MySQL优化三(InnoDB优化)

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MySQL优化三(InnoDB优化)

学习计划很容易就被打断,坚持也不容易。最近公司里开会,要调整业务方向,建议学习NodeJS。NodeJS之前我就会一点,但是没有深入研究。Node的语法和客户端Js基本上是一样的,这半年来很少开发有客户端的东西。本来JS基础还行的我,也对这块的知识陌生了。看起来知识都是用进废退的,不常用了,过不了多久就会遗忘。所以又重新复习了JS的相关知识。学习了Node的服务器与socket知识。MySQL的计划就这样的搁浅起来,星期天的时候吃吃喝喝睡睡,早上又懒的要命,熬着熬着就熬到了下午。废话不多说了,继续进行MySQL的优化系列,这次看下InnoDB的优化项。

InnoDB的主索引是聚簇索引,索引与数据公用表空间。对于InnoDB来说,数据就是索引,索引就是数据。InnoDB缓存机制与MyISAM的最大区别在于,InnoDB不仅缓存索引,同时还会缓存数据。

一、InnoDB缓存池

InnoDB缓存池(InnoDB buffer pool)是提升InnoDB提升性能的关键,它既可以缓存数据,又可以缓存索引,甚至其他的管理数据(元数据、行级锁)等。可以使用show variables like 'innodb%pool%'; 来查看相关的参数选项。

mysql> show variables like 'innodb%pool%';
+-------------------------------------+----------------+
| Variable_name | Value |
+-------------------------------------+----------------+
| innodb_additional_mem_pool_size | 8388608 |
| innodb_buffer_pool_dump_at_shutdown | OFF |
| innodb_buffer_pool_dump_now | OFF |
| innodb_buffer_pool_filename | ib_buffer_pool |
| innodb_buffer_pool_instances | 8 |
| innodb_buffer_pool_load_abort | OFF |
| innodb_buffer_pool_load_at_startup | OFF |
| innodb_buffer_pool_load_now | OFF |
| innodb_buffer_pool_size | 134217728 |
+-------------------------------------+----------------+

innodb_buffer_pool_size

innodb_buffer_pool_size是用于设置InnoDB缓存池(InnoDBBufferPool)的大小,默认值是128M.InnoDB缓存池的大小对InnoDB的整体性能影响较大,如果当前的MySQL服务器专门用作MySQL服务,那么可以尽量的增加该参数的大小。

innodb_buffer_pool_instance

innodb_buffer_pool_instance默认值是1,表示InnoDB缓存池被划分为一个区域,适当的增加该参数值,可以提升InnoDB的并发性能。

innodb_additional_mem_pool_size

指定InnoDB用于来存储数据字典和其他内部数据的缓存大小,默认值是2M.InnoDB的表个数越多,就应该适当的增加该参数的大小。

二、InnoDB缓存池内部结构

InnoDB在内存中维护一个缓存池用于缓存数据和索引。缓存池可以认为是一条很长的链表(list).该链表分为两个子链表,一个子链表存放old page数据,old page 数据是长时间未被访问的数据页,亮一个子链表存放new page,new page 是最近被访问的数据页。old page 默认占整个链表大小的37%,可以通过innodb_old_blocks_pct参数查看.

mysql> show variables like 'innodb_old_blocks%';
+------------------------+-------+
| Variable_name | Value |
+------------------------+-------+
| innodb_old_blocks_pct | 37 |
| innodb_old_blocks_time | 1000 |
+------------------------+-------+

old page 和 new page 的交汇点称为midpoint。

当用户访问数据时,InnoDB首先会再InnoDB缓存中查找数据,如果缓存池中没有数据,InnoDB会将硬盘中的数据插入到InnoDB缓存池中,如果缓存池已满,则利用LRU算法清楚过期的老数据

三、InnoDB缓存池预热。

MySQL服务器启动一段时间后,InnoDB会将经常访问的数据(业务数据,管理数据)放入InnoDB缓存中,即InnoDB缓存池中保存的是频繁需要访问的数据(简称热数据)。当InnoDB缓存池的大小是几十G或者上百G的时候,如果重启MySQL,如果将之前InnoDB缓存池中的热数据加载到InnoDB缓存池中呢?

如果单靠InnoDB自身预热的InnoDB缓存池,将会是一个不短的时间周期,这对于业务繁忙的系统来说,长时间的挂机,是严重的生产事故,不能够容忍。幸好在MySQL5.6版本支持关闭服务时,可以将热数据保存至硬盘,MySQL重启是首先将硬盘中的热数据加载到InnoDB的缓存中去,这样可以缩短预热的时间,提高业务繁忙高并发时的效率。

mysql> show variables like '%innodb%pool%';
+-------------------------------------+----------------+
| Variable_name | Value |
+-------------------------------------+----------------+
| innodb_additional_mem_pool_size | 8388608 |
| innodb_buffer_pool_dump_at_shutdown | OFF |
| innodb_buffer_pool_dump_now | OFF |
| innodb_buffer_pool_filename | ib_buffer_pool |
| innodb_buffer_pool_instances | 8 |
| innodb_buffer_pool_load_abort | OFF |
| innodb_buffer_pool_load_at_startup | OFF |
| innodb_buffer_pool_load_now | OFF |
| innodb_buffer_pool_size | 134217728 |
+-------------------------------------+----------------+

innodb_buffer_pool_dump_at_shutdown

默认是关的,如果开启参数,停止MySQL服务是,InnoDB缓存中的热数据将会保存到硬盘中。

innodb_buffer_pool_load_at_starup

默认是关闭的,如果开启该参数,启动MySQL服务时,MySQL将本地硬盘的热数据加载到InnoDB缓存池中。

innodb_buffer_pool_dump_now

默认关闭,如果开启该参数,停止MySQL服务时,以手动方式将InnoDB缓存池中的热数据保存到本地硬盘。

innodb_buffer_pool_load_now

默认关闭,如果开启该参数,启动MySQL服务时,以手动方式将本地硬盘的数据加载到InnoDB缓存池中,

innodb_buffer_pool_filename

如果开启InnoDB预热功能,停止MySQL服务是,MySQL将InnoDB缓存池中的热数据保存到数据库根目录下,默认文件名是这个参数的值。

开启InnoDB缓存后,可以使用如下命令查看当前InnoDB缓存池预热的状态信息:

show status like 'innodb_buffer%';
+---------------------------------------+-------------+
| Variable_name | Value |
+---------------------------------------+-------------+
| Innodb_buffer_pool_dump_status | not started |
| Innodb_buffer_pool_load_status | not started |
| Innodb_buffer_pool_pages_data | 218 |
| Innodb_buffer_pool_bytes_data | 3571712 |
| Innodb_buffer_pool_pages_dirty | 0 |
| Innodb_buffer_pool_bytes_dirty | 0 |
| Innodb_buffer_pool_pages_flushed | 1 |
| Innodb_buffer_pool_pages_free | 7973 |
| Innodb_buffer_pool_pages_misc | 0 |
| Innodb_buffer_pool_pages_total | 8191 |
| Innodb_buffer_pool_read_ahead_rnd | 0 |
| Innodb_buffer_pool_read_ahead | 0 |
| Innodb_buffer_pool_read_ahead_evicted | 0 |
| Innodb_buffer_pool_read_requests | 1497 |
| Innodb_buffer_pool_reads | 219 |
| Innodb_buffer_pool_wait_free | 0 |
| Innodb_buffer_pool_write_requests | 1 |
+---------------------------------------+-------------+

这里面的英语都比较简单,就不解释了。

四、InnoDB实时监控

mysql> show engine innodb status\G

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