MySQL slow query - “Waiting for query cache lock”

Question

I am running a simple query on a simple table on the same machine as the server running 5.5. It is taking 22sec to return ~7000 rows from a 20 million row table. Upon prof

Answer 1

This is a known problem with MySQL. It's really well described here:

https://web.archive.org/web/20160129162137/http://www.psce.com/blog/kb/how-query-cache-can-cause-performance-problems/

Query cache can help you a lot but at the same time it can become a bottleneck.