The hsha (half-synchronous, half-asynchronous) Thrift server was rewritten on top of Disruptor for Cassandra 2.0 [1] to unlock substantial performance benefits over the old hsha. Unfortunately, the rewrite introduced a bug that can cause incorrect data to be sent from the coordinator to replicas. I apologize that it took so long for us to realize what was causing the compaction errors reported as far back as November.
Who is affected: anyone running the hsha server in a 2.0.x release for x < 6. Who is NOT affected: anyone using the native protocol or the default sync Thrift server. 2.0.6 has a fix and is expected to be released Monday; you can grab the pre-release build from [3], or apply the patch from [4] yourself. [1] https://issues.apache.org/jira/browse/CASSANDRA-5582 [2] https://issues.apache.org/jira/browse/CASSANDRA-6285 [3] http://people.apache.org/~slebresne/ [4] https://issues.apache.org/jira/secure/attachment/12632583/CASSANDRA-6285-disruptor-heap.patch -- Jonathan Ellis Project Chair, Apache Cassandra co-founder, http://www.datastax.com @spyced