This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
You need to track what the garbage collector is doing. See my paper at ceCMG for one way you could do this. (And no, using JConsole does not provide the necessary information - you need to know how much heap space is in use after each major collection.)