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