Mysql cache issues?

Question

Could Mysql cache cause a performance penalty, when invalidating queries of a big Mysql cache zone?. I mean... I had a server with 16GB of cache memory and when a big table full update was done... a performance issue was suffered (seem not to be due to cache invalidation!!)... apparently this performance issue was much more notorious when the cache had been feeding some time and was near the top of the cache (arriving to 16GB) than when the query cache memory usage for example was much far more smaller... for example of 2GB ram... of cached content....

Does it exist any kind of explanation for this sensation?.

Comments

Spot on. I tend to keep 200MB caches for some webservers, and that's already considered fairly large.

The qcache does lookups based on the EXACT query text, I presume by using a hash index; but that makes it highly inefficient at removing the cache entries for a particular table.

Answer 1

Could Mysql cache cause a performance penalty, when invalidating queries of a big Mysql cache zone?

can, and *will* ... see also http://dom.as/tech/query-cache-tuner/ cache is locked while entries are being purged to prevent handing out cached results that may already be out-of-date, and the more active cache entries that need to be purged the longer it stays locked ...