It converts mysql-proxy into a query cache for all 'SELECT' queries.
All cached data is stored directly in mysql-proxy using a Least-Recently-Used
cached strategy. So if the cache goes full the oldest entry gets removed to
store the new one.
Furthermore each entry has a lifetime. Is this lifetime reached, the entry in
the cache is removed and refreshed with data from mysqldb behind the proxy.
This refresh makes the entry also 'younger', so it is less likely to be removed
if the cache goes full.