MySQL - 存储引擎之InooDB后台线程

后台线程

作用： 将InnoDB缓冲池的数据，在合适时机刷新到磁盘当中

线程分类：

1.Master Thread： 核心后台线程，负责调度其他线程，还负责将缓冲池中的数据异步刷新到磁盘中，保持数据的一致性，还包括脏页的刷新、合并插入缓存、undo页的回收
2.IO Thread： 在InnoDB存储引擎中大量使用了AIO来处理IO请求，这样可以极大地提高数据库的性能，而IO Thread主要负责这些IO请求的回调

线程类型	默认个数	职责
Read thread	4	负责读操作
Write thread	4	负责写操作
Log thread	1	负责将日志缓冲区刷新到磁盘
Insert buffer thread	1	负责将写缓冲区内容刷新到磁盘

通过show engine innodb status查看具体情况

    --------
    FILE I/O
    --------
    I/O thread 0 state: waiting for completed aio requests (insert buffer thread)
    I/O thread 1 state: waiting for completed aio requests (log thread)
    I/O thread 2 state: waiting for completed aio requests (read thread)
    I/O thread 3 state: waiting for completed aio requests (read thread)
    I/O thread 4 state: waiting for completed aio requests (read thread)
    I/O thread 5 state: waiting for completed aio requests (read thread)
    I/O thread 6 state: waiting for completed aio requests (write thread)
    I/O thread 7 state: waiting for completed aio requests (write thread)
    I/O thread 8 state: waiting for completed aio requests (write thread)
    I/O thread 9 state: waiting for completed aio requests (write thread)
    Pending normal aio reads: [0, 0, 0, 0] , aio writes: [0, 0, 0, 0] ,
     ibuf aio reads:, log i/o's:, sync i/o's:
    Pending flushes (fsync) log: 0; buffer pool: 0
    584 OS file reads, 247 OS file writes, 69 OS fsyncs
    0.00 reads/s, 0 avg bytes/read, 0.00 writes/s, 0.00 fsyncs/s

3.Purge Thread： 主要用于回收事务已经提交的undo log，在事务提交之后，undo log可能不用了，就用它来回收
4.Page Cleaner Thread： 协助Master Thread刷新脏页到磁盘的线程，它可以减轻Master Thread的工作压力，减少阻塞