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How to optimize I/O?
Posted by: gpslocator
Date: May 09, 2007 09:41PM

I have a MyISAM table that has 1,864,299 records. I want to imporve its query performance hence I preload the index of the table into key cache by using "load index into cache".

But the result make me despaired. Below is the benchmark data:

records time(ms)
------------------------
158776 305984 (with index caching)
184587 91906 (without index caching)

190184 1119015 (with index caching)
195491 98172 (without index caching)

The key buffer size is 256MB. The cached index only uses 224.2MB.
With cached index, MySQL will have 100% hitrate and low traffic 20~60kb.
But with none cached index, MySQL will have 82% hitrate and high traffic 200~600kb.
Why cached index decrease the I/O performance so heavily cause all performance is down? And how to improve the I/O performance?

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