Have a look at this

https://issues.apache.org/jira/browse/CASSANDRA-2787

Thanks,
Nehal Mehta

2011/10/1 Radim Kolar <hsn@sendmail.cz>
1.
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

2.
Cassandra needs jamm just until first CF flush is done because it knows live to serialized ratio from flush?