get-connection attempts class loading and driver manager invocation every time

[seancorfield]

This is really only needed once per class name so it could be cached.

[seancorfield]

next.jdbc calls DriverManager/getLoginTimeout on every connection attempt -- that could be moved into get-datasource -- and it already mitigates the problem that clojure.java.jdbc has, because the class loading is done in get-datasource, not get-connection.

That said, it's probably still worth optimizing/caching for programs that create multiple data sources or are very naive about calling get-connection.