在 MySQL 中，innodb_io_capacity参数控制着InnoDB引擎刷脏页的能力。该参数设置得过小会导致MySQL刷脏页能力不足，从而影响性能；设置得过大会让MySQL认为IO能力很强，会造成IO尖峰。合理地设置innodb_io_capacity值可以控制刷脏页的速度，进而提高数据库性能。

innodb_io_capacity参数的默认值是200，单位是页，该参数设置的大小取决于硬盘的IOPS，即每秒的输入输出量（或读写次数）。一般情况下，对于高转速磁盘，可以适当提高该参数的值；在SSD磁盘配置下，可以将该值调整为5000-20000；在pcre-ssd配置下，可以将该值调整为更高，大约50000。

官方的解释：
The innodb_io_capacity variable defines the number of I/O operations per second (IOPS)
available to InnoDB background tasks, such as flushing pages from the buffer pool and merging data from the change buffer.

The innodb_io_capacity variable defines the overall I/O capacity available to InnoDB. It should be set to approximately the number of I/O operations that the system can perform per second (IOPS).When innodb_io_capacity is set, InnoDB estimates the I/O bandwidth available for background tasks based on the set value.