MySQL Forums
Forum List  »  Performance

Re: Key Efficiency Graph
Posted by: Bill Karwin
Date: May 25, 2006 11:32AM

A higher hitrate in a caching system is good.

It means that requests for elements in the index are getting satisfied by the cache, instead of being required to go to the disk to load them. That's what a "hit" means for a cache: the requested data was supplied by the cache, instead of the disk.

Initially, the cache is empty, so the hit rate will be low. As indexes are loaded into the cache, subsequent requests for those indexes will be satisfied by the cache. If your cache is large enough to store all the indexes that are requested, the hit rate should reach 100%. That's good.

If your cache isn't configured large enough to hold the indexes, requests for those indexes cause parts of the index to be reloaded into the cache from disk, which cause sother parts of the index to be expelled from the cache. This would translate into a lower average hit rate, and it should be avoided.

You _can_ control the hit rate, by reducing the amount of memory allocated to key buffers until it's less than the size of your indexes! ;-) If you do this, be prepared for your disk activity to go way up, and your site's performance to go way down.

Regards,
Bill K.

Options: ReplyQuote


Subject
Views
Written By
Posted
14017
May 25, 2006 05:56AM
Re: Key Efficiency Graph
8269
May 25, 2006 11:32AM
3537
May 25, 2006 05:55PM


Sorry, you can't reply to this topic. It has been closed.

Content reproduced on this site is the property of the respective copyright holders. It is not reviewed in advance by Oracle and does not necessarily represent the opinion of Oracle or any other party.