http://www.aichengxu.com/article/Java/18368_2.html
https://blogs.oracle.com/poonam/entry/understanding_cms_gc_logs
http://www.theserverlabs.com/blog/2010/05/26/human-readable-jvm-gc-timestamps/
-Xloggc:<file_name> –XX:+PrintGCDetails -XX:+PrintGCDateStamps
Unfortunately -XX:+PrintGCDateStamps is available only for Java 6 Update 4 and later JVMs.
http://blog.csdn.net/v1v1wang/article/details/6112311