The run-class.sh script defaults to setting up a gc.log file, if SAMZA_OPTS is undefined.
Newer versions of Java 6, and Java 7 allow you to roll gc log files with -XX:+UseGCLogFileRotation. See http://stackoverflow.com/questions/3822097/rolling-garbage-collector-logs-in-java for details.
Should also validate that the change doesn't break with older Java 6 versions.
Also, Suresh Srinivas was saying that there's an alternate way to do this. Suresh - care to chime in?