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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 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.

Status variables


Option Description
Scope: Global
Data type: Numeric

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

Other reading

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Last update: 2023-09-27