We are running a 6-node cluster in amazon cloud (2 nodes in each availability zone). The ec2 instances are m1.large and we have 256 vnodes on each node.
We are using Ec2Snitch, NetworkTopologyStrategy and a replication factor of 3. When we decommission one node suddenly reads and writes start to fail. We are seeing Not Enough Replicas error messages which doesn't make sense even though we are doing QUORUM reads/writes because there should still be 2 copies of each piece of data in the cluster. Digging deep in the logs we see that the phi_convict_threshold is being exceeded so all nodes in the cluster are being marked down for a period of approximately 10 seconds. *Why on earth is the decommissioning of one node causing all the nodes to be marked down?* We have two ways to work around this, though we think we have found the ultimate cause of the problem. 1) If we set the phi_convict_threshold to 12 or higher the nodes never get marked down. 2) or If we set the vnodes to 16 or lower we never see them get marked down. *Is either of these solutions dangerous or better than the other?* The ultimate cause of the problem appears to be that the calculatePendingRanges in StorageService.java is an extremely expensive process and is running in the same thread pool (GossipTasks) as the Gossiper.java code. calculatePendingRanges() runs during state changes of nodes (ex. decommissioning). During this time it appears that it is hogging the one thread in the GossipTasks thread pool thus causing things to get marked down from FailureDetector.java. -- John Pyeatt Singlewire Software, LLC www.singlewire.com ------------------ 608.661.1184 john.pye...@singlewire.com
