This week's book giveaway is in the Reactive Progamming forum. We're giving away four copies of Reactive Streams in Java: Concurrency with RxJava, Reactor, and Akka Streams and have Adam Davis on-line! See this thread for details.
The documentation for log4j addresses that issue specifically. Read it here: http://logging.apache.org/log4j/1.2/manual.html and look at the section headed "Performance". Also bear in mind that it was written over a decade ago and any specific numbers mentioned apply to decade-old computers.
Acetylsalicylic acid is aspirin. This could be handy too: