MySQL技术内幕InnoDB存储引擎 - 后台线程

1、Master Thread

一个非常核心的后台线程。

主要负责将缓冲池中的数据异步刷新到磁盘，

保证数据的一致性：包括脏页的刷新、合并插入缓冲（ INSERT BUFFER ）、UNDO 页的回收等。

随着版本的发展，不少工作分出去给其他线程去做了：

　　a、UNDO 页的回收工作交给 Purge Thead

　　b、脏页的刷新工作交给 Page Cleaner Thread

 

 

2、IO Thread

InnoDB中大量使用了AIO(Async IO)处理写IO的请求以提交性能，

IO Thread的主要工作就是处理这些IO请求的回调处理。

通过下面的命令可以查看 io 线程的数量：

SHOW VARIABLES LIKE 'innodb_%io_threads';

innodb_read_io_threads    4
innodb_write_io_threads    4

也可以通过 查看每个：

show engine innodb status

...
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: 3
1627 OS file reads, 1175632 OS file writes, 477732 OS fsyncs
0.00 reads/s, 0 avg bytes/read, 0.54 writes/s, 0.23 fsyncs/s
...

 

3、Purge Thread

负责回收和分配 undo页。

SHOW VARIABLES LIKE 'innodb_purge_threads'

innodb_purge_threads    4

 

4、Page Cleaner Thread

负责脏页的刷新操作。