Tài liệu High Availability MySQL Cookbook phần 10

Now we have seen how to monitor the IO performance of the system and briefly discussed the
meaning of the numbers that come out of the monitoring tools; this section looks at some of
the practical and immediate things that we can tune.
The Linux kernel comes with multiple IO schedulers, each of which implement the same
core functions in slightly different ways. The first function merges multiple requests into one
(that is, if three requests are made in a very short period of time, and the first and third are
adjacent requests on the disk, it makes sense to merge them and run them as one single
request). The second function is performed by a disk elevator algorithm and involves ordering
the incoming requests, much as a elevator in a large building must decide in which order to
service the requests.