2.1 INFO is the level you should assume the software will be run in.
INFO messages are things which are not bad but which the user will definitely want to know about
2.2 TRACE and DEBUG are both things you turn on when something is wrong and you want to figure out
what is going on. DEBUG should not be so fine grained that it will seriously effect the performance
of the server. TRACE can be anything. Both DEBUG and TRACE statements should be
wrapped in an if(logger.isDebugEnabled) if an expensive computation in the argument list of log method call.
2.3 WARN and ERROR indicate something that is bad. Use WARN if you aren't totally sure it is bad,
2.4 Use FATAL only right before calling System.exit().