>> Server version is 5.5.1
Why are you using old non G.A release? There are significant improvements made since 5.5.1 but unfortunately MyISAM hasn't been getting major improvements for many years so if you are using only MYISAM storage engine then it's probably okay.
The key cache miss rate can be calculated as Key_reads/Key_read_requests= 0.04
So, it not too bad. You should be aware that MyISAM only cache indexes in memory and it lets O/S to cache it's data pages in memory. So you should keep key cache size i.e. up to 20% of the available RAM, so that OS can cache more data in memory. Typically you do not need all your indexes to be in memory only those portions of them which are accessed frequently. The size of this “working set” can greatly depend on application and can range from 5% of total size or less to almost 100%. When your go from working set what fits in memory to the one which does not any more performance can degrade 10 or more times.
Are you having any performance issue? What do you see in MySQL slow query log?
There is good article about key cache hit ratio, see:
http://www.mysqlperformanceblog.com/2010/02/28/why-you-should-ignore-mysqls-key-cache-hit-ratio/
Edited 2 time(s). Last edit at 08/19/2012 05:18AM by Aftab Khan.