This driver uses a database table to store the cache. The newest versions of
MySQL and SQLite work are known to work. Other RDBMSes should work.

Why cache things in a database? Isn't the database what people are trying to
avoid with caches? This is often true, but a simple primary key lookup is
extremely fast in many databases and this provides a shared cache that can be
used when less reliable storage like memcached is not appropriate. Also, the
speed of simple lookups on MySQL when accessed over a local socket is very hard
to beat. DBI is fast.