Warning about different commitlog_directory

Question

Is it bad to have a different commitlog_directory per node? OpsCenter is printing the following error in its log:

 ERROR: Problem while calling CassandraConfDcController (ConfMismatch): The confs across your Cassandra nodes do not match. The following groups of nodes have matching configs:

    <host1>
    <host2>

     The following conf options differ across nodes:

     commitlog_directory
      File "/usr/share/opscenter/lib/py-redhat/2.6/shared/amd64/twisted/internet/defer.py", line 1020, in _inlineCallbacks
        result = g.send(result)

      File "/usr/lib/python2.6/site-packages/opscenterd/WebServer.py", line 452, in get_cassandra_conf

      File "/usr/lib/python2.6/site-packages/opscenterd/WebServer.py", line 393, in assert_conf_matches

Both nodes are Cassandra nodes. The reason why I have mismatching commitlog_directory is that host1 has smaller partition sizes so I moved the commitlog dir into separate partition

Answer 1

There may certainly be valid reasons for the commitlog_directory option not being homogenous across all nodes. The message you see in the logs is overly ominous, and in valid cases can be ignored.

Typically that occurs when clicking "Configure Cluster" from the OpsCenter UI, which prefills all cassandra.yaml options based on the values from an existing nodes. The message displayed means that because nodes do not have identical config values, OpsCenter can't pick a node to use as a template, so it puts that choice in the user's hands.