Question

I’ve look all over the web and in the questions asked here about MySQL caching and most of them seem very non-specific about a couple of questions that I have about performance and MySQL query caching. Specifically I want answers to these questions, assume for all questions that I have the query cache enabled and it is of type 2, or “DEMAND”:

1. Is the query cache per table, per database, or per server? Meaning if I have the cache size set to X and have T tables and D databases will I be caching TX, DX, or X amount of data?
2. If I have table T1 which I regularly use the SQL_CACHE hint on for SELECT queries and table T2 which I never do, when I query T2 with a SELECT query will it check through the cache first before performing the query? Note: I don’t want to use the SQL_NO_CACHE for all T2 queries.
3. Assume the same situation as in question 2. If I alter (INSERT, DELETE) table T2 will any processing be done on the cache?
4. For answers to 2 and 3, is this processing time negligible if T2 is constantly being altered and is the target of a majority of my SELECT queries?

Answer 1

1. It’s per instance
2. Yes
3. Yes
4. Yes

http://dev.mysql.com/doc/refman/5.1/en/query-cache-operation.html