It's useful to have debug logging capabilities at low level on Java driver implementation, so that we can detect in logs when a call is about to be made to the server, and when that call returns. Not totally clear to me how low in the stack that this should be done (maybe com.mongodb.DBPort#go or com.mongodb.DBTCPConnector#call?).

This is very useful for debugging, in order to correlate hung threads with specific calls to the server process.