https://book.2cto.com/201402/40300.html
在MySQL5.1.X版本中，innodb_file_io_threads參數默認是4，該參數在Linux系統上是不可更改的，但Windows系統上可以調整。這個參數的作用是：InnoDB使用后台線程處理數據頁上讀寫I/O（輸入輸出）請求的數量。
在MySQL5.5.X版本中，或者說是在InnoDB Plugin1.0.4以后，就用兩個新的參數，即innodb_read_io_threads和innodb_write_io_threads，取代了innodb_file_io_threads如此調整后，在Linux平台上就可以根據CPU核數來更改相應的參數值了，默認是4。
假如CPU是2顆8核的，那么可以設置：
innodb_read_io_threads = 8
innodb_write_io_threads = 8
如果數據庫的讀操作比寫操作多，那么可以設置：
innodb_read_io_threads = 10
innodb_write_io_threads = 6
也就是說，你可以根據情況加以設置。
注意
這兩個參數不支持動態改變，需要把該參數加入my.cnf里，修改完后重啟MySQL服務，允許值的范圍是1～64。
調整完成后，你可以用命令“show engine innodb status\G;”來查看調整結果，如下所示：
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)
關於innodb_read_io_threads和innodb_write_io_threads參數的含義，請參見MySQL5.5 手冊：