-XX:+UseCompressedStrings is actually dropped in jdk7, but the Tuning Guide(http://spark.incubator.apache.org/docs/latest/tuning.html) is still recommend users to use this. JVM will warn us "Java HotSpot(TM) 64-Bit Server VM warning: ignoring option UseCompressedStrings; support was removed in 7.0" if we use this option. so,maybe we can remove the point from the guide now.
If the option is added back in the future, we also can add it back to the guide.
more details can access this url : http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7129417