Hello, Yesterday we ran into a serious issue while joining a new node to our existing 4 node Cassandra cluster (version 2.0.7). The average node data size is 152GB's with a replication factor of 3. The node was prepped just like the following document describes - http://docs.datastax.com/en/cassandra/2.0/cassandra/operations/ops_add_node_to_cluster_t.html.
When I started the new node, Opscenter showed the node as "Active - Joining" but we immediately began getting timeouts on our websites because lookups were taking too long. On the 4 existing nodes the network interface showed about 200Mbps being used, the CPU never went over 20% and the memory usage barely changed. The question I have is, does adding a new node cause some sort of throttling that would affect our webservers from being able to function as normal? The only thing that we can think of that might have had some affect was that a repair was just finishing on one of the nodes when the new node was added. The repair ended up finishing while the new node was in the joining state but the timeouts did not go away afterwards. Our impatience got the better of us so we ended up stopping the Cassandra service on the new node because it appeared, at the time, to have stalled out in the joining state and nothing more was being streamed to it. But even stopping it did not allow the cluster to resume its normal operation and we were still getting timeouts. We tried rebooting our web servers and then our 4 existing Cassandra servers but none of it worked. We never saw any errors/exceptions in the Cassandra and system logs at all. It completely mystified us why there would be no errors/exceptions unless this was working as intended. We ended up getting it working by adding the new node again and just letting it go until it finally finished joining, and everything magically started working again. We noticed towards the end it was barely streaming anything (Opscenter was not showing any running streams towards the end) by checking the size of the data directory and we saw it growing and shrinking ever so slightly. We have to add one more new node and then decommission two of the existing nodes so we can perform some hardware maintenance on the server those two existing nodes are on, but we are hesitant to try this again without scheduling a maintenance window for this node add and decommissioning process. So to reiterate what I am asking, does adding a node cause the cluster to be unusable/timeout? Also, can we expect the decommissioning of the other two nodes to cause the same type of downtimes since they have to stream their content out to the other nodes in the cluster? Thanks, Thomas Miller
