There's an issue with logging of JDBC objects such that means that you won't see any JDBC logging if java.sql.Connection logging isn't enabled.
To quote Jeff Butler:
This is related to a structural defect in the way iBATIS does logging. iBATIS does logging through dynamic proxies for all the JDBC objects - and these objects are only proxied if the Connection object itself is proxied. The Connection object is proxied only if debugging is enabled for it. So, you'll not get any logging unless debugging is enabled for Connection.
Seen in 2.3.0 (and previous)