Some improvements to Query Cache text (by Colin Faber).

@itemize @bullet

@item

If you don't use the query cache (@code{query_cache_size=0}), there is

no notable overhead.

@item

If all queries are very simple (like selecting a row from a table with

one row) but still different so that the queries can't be cached, the

overhead for having the query cache active is 13%. This could be

regarded as the worst case scenario. In real life queries are much more

complicated than this so the overhead is normally significantly lower.

If want to disable the query cache code set @code{query_cache_size=0}.

By disabling the query cache code there is no noticeable overhead.

@item

If all of the queries you're preforming are simple (such as selecting a

row from a table with one row); but still differ so that the queries can

not be cached, the overhead for having the query cache active is 13%.

This could be regarded as the worst case scenario. However, in real life,

queries are much more complicated than our simple example so the overhead

is normally significantly lower.

@item

Searches after one row in a one row table is 238% faster.

This can be regarded as close to the minimum speedup to be expected for