Cassandra: Hanging node tool repair

Question

We had 3 regions for the cassandra cluster each with 2 nodes, totally 6. Then we have added 3 more regions now totally we have 12 cassandra nodes in the cluster. After adding the nodes, we have updated the replication factors and started the nodetool repair. But the command is hanging for more than 48+ hours and not finished yet. When we looked into the logs 1 or 2 AntiEntropySessions are pending still, because some of the CF's are not fully synced. All AntiEntropySessions are getting the merkle tree successfully from all the nodes for all CF's. But some repair b/w some nodes are not completed for some CF's, so it leads to pending AntiEntropySessions and the repair is hanging.

We are using Cassandra 1.1.12. We will not able to upgrade the Cassandra now. We have restarted the nodes and started the repair again but it still hangs. We have observed one CF which has frequent read and writes in the initial 3 regions which is active during the repair is failing to sync completely in all the times.

Is that necessary that while running repair there shouldn't be any read/writes in any CF? OR suggest me what could be the issue here?

Answer 1

Cassandra 1.1 is very old so its hard to remember exact issues, but there was problems with streaming then which would possibly hang. Some causes were things like if a read was timed out or was connection was reset. Since you are past 1.1.11 though your Ok to try subrange repairs.

Try to find an appropriate token range you can repair in an hour (keep running smaller and smaller range until you can complete it), set a timeout of a couple hours. Expect some repairs to fail (timeout) so just retry them until they complete. If you cannot get it after many retries continue to make that subrange smaller, but even then it may have problems if you have a partition thats very wide (can check with nodetool cfstats) that will make it much worse.

Once you get a completed repair, upgrade like crazy.