> I have 9 node cluster with RF-3 and using Cassandra0.70/Hector26. Recently > we are seeing lot of "UnavailableException" at the client side. Whenever > this happens, I found following pattern in Cassandra node's log file at that > given time,
UnavailableException is the expected error if an insufficient number of nodes are up in the replicate set for the row you're reading/writing. "Up" in this case means according to gossip (what you see with nodetool ring). The question is really why nodes are being marked as down and whether it's legitimate or not. There is https://issues.apache.org/jira/browse/CASSANDRA-2554 which may be relevant, but simple overload is also a possible reason. -- / Peter Schuller
