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Multiple page asynchronous I/O requests

The I/O unit size in InnoDB is only one page, even if the server is doing read ahead. A 16KB I/O unit size is 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 once, Linux internally can merge requests, and reads are more efficient. This feature can submit multiple page I/O requests and works in the background.

You can manage the feature with the linear read-ahead technique. The technique adds pages to the buffer pool based on the buffer pool pages being accessed sequentially. The configuration parameter, innodb_read_ahead_threshold controls this process.

On an 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

  • Percona Server 5.7.20-18: Feature ported from the Facebook MySQL patch.

Status Variables

Innodb_buffered_aio_submitted

Implemented in Percona Server 5.7.20-18.

Option Description
Data type Numeric
Scope Global

This variable shows the number of submitted buffered asynchronous I/O requests.

See also

Optimizing full table scans in InnoDB

Bug #68659 InnoDB Linux native aio should submit more i/o requests at once