Ubuntu Unleashed 2013 Edition: Covering 12.10 and 13.04, Eighth Edition

Using the Query Cache

Newer versions of MySQL allow you to cache the results of queries so that, if new queries come in that use the same SQL, the result can be served from RAM. In some ways the query cache is quite intelligent: If, for example, part of the result changes due to another query, the cached results are thrown away and recalculated next time. However, in other ways it is very simple. For example, it uses cached results only if the new query is exactly the same as a cached query, even down to the capitalization of the SQL.

The query cache works well in most scenarios. If your site has an equal mix of reading and writing, the query cache does its best but is not optimal. If your site is mostly reading with few writes, more queries ...