6u14p 64bit JVM (with compressed OOPs turned off) hung at Full GC, while attempting to print out the “before GC” object histogram. Note the following flags were on.
-XX:+PrintClassHistogramAfterFullGC -XX:+PrintClassHistogramBeforeFullGC
-XX:+PrintClassHistogramAfterFullGC -XX:+PrintClassHistogramBeforeFullGC