Multiple page asynchronous I/O requests¶
The I/O unit size in InnoDB is only one page, even if the server doing read ahead. A 16KB
I/O unit size is too small for sequential reads, and less efficient than a larger I/O unit size. InnoDB uses Linux asynchronous I/O (
aio) by default. By submitting multiple, consecutive 16KB read requests at the same time, Linux internally merges the requests and
reads more efficiently.
This feature is able to submit multiple page I/O requests and works in the background. You can manage the feature with the linear read-ahead technique. This technique adds pages to the buffer pool based on the buffer pool pages being accessed sequentially. The
innodb_read_ahead_threshold configuration parameter controls this operation.
On a HDD RAID 1+0 environment, more than 1000MB/s disk reads can be achieved by submitting 64 consecutive pages requests at once, while only 160MB/s disk reads is shown by submitting single page request.
Version Specific Information¶
- 8.0.12-1 - The feature was ported from Percona Server for MySQL 5.7.
This variable shows the number of submitted buffered asynchronous I/O requests.