Have a look at this
jamm still do not works on openJDK?
WARN [MutationStage:368] 2011-10-01 18:21:39,695 Memtable.java (line 156) MemoryMeter uninitialized (jamm not specified as java agent); assuming liveRatio of 10.0. Usually this means cassandra-env.sh disabled jamm because you are using a buggy JRE; upgrade to the Sun JRE instead
Cassandra needs jamm just until first CF flush is done because it knows live to serialized ratio from flush?