I've just opened a new JIRA: CASSANDRA-4142 I've double checked numbers, 7747 seems to be array list object's capacity (Eclipse Memory Analyzer displays "java.lang.Object[7747] @ 0x7d3f3f798"). Actually there are 5757 browsable entries in EMA therefore each object is about 140 KB (size varies between 143088 bits and 143768 bits).
We have no pending compactions tasks. Our cluster is currently under-loaded. Our goal is to handle hundreds of tera bytes which explains 1 TB per node. Our need is to archive data so our cluster is not running under a read-heavy load. @Dave Brosius: I made a mistake. To be correct 786 MB is 47% of *leak suspects* as reported by Eclipse Memory Analyser. Our Cassandra nodes are pretty standard: 10 GB of ram with Xmx set to 2,5 GB. Regards, Romain