I got a very weird problem. I enabled mysql query cache to speed up my application I am writing myself. This application includes a ajax chatbox and behind an authentication. I chose the cache type as DEMAND so I can decide which queries to cache. It works very nicely and the chatbox performance has been improved by a lot.
My problem is the value of 'Qcache_not_cached' which does not stop increasing although I have made sure my queries all should be cached as they are all small and don't often change value. I even disabled all queries by SQL_NO_CACHE which stoped the increase of 'Qcache_hits' as it should, but not the increase of 'Qcache_not_cached' . Does this mean all queries that I decided not to cache are counted against 'Qcache_not_cached' ? This is at least not so documented ...
Never mind, by writing this post I came up with the right search term for google and found this:
The Qcache_not_cached counter provides insight into the number of statements executed against MySQL that were not cacheable, due to either being a non-SELECT statement or being explicitly barred from entry with a SQL_NO_CACHE hint.