The schema has not settled in 10 seconds; further migrations are ill-advised until it does.?

[Yan Chunlu]

I have encountered this problem while update the key cache and row cache.  I
once updated them to "0"(disable) while node2 was not available, when it
comeback they eventually have the same schema version.

[default@prjspace] describe cluster;
Cluster Information:
   Snitch: org.apache.cassandra.locator.SimpleSnitch
   Partitioner: org.apache.cassandra.dht.RandomPartitioner
   Schema versions:
        79d072cc-cc62-11e0-a753-5525ca993302: [node3, node1, node2]



ever time I change the row cache && key cache back per CF, it show the
following error:

[default@prjspace] update column family CommentCache with
keys_cached=200000;


Waiting for schema agreement...
Warning: unreachable nodes node3The schema has not settled in 10 seconds;
further migrations are ill-advised until it does.
Versions are
f7f24ef4-caf7-11e0-9b1d-5525ca993302:[node1],79d072cc-cc62-11e0-a753-5525ca993302:[node2],UNREACHABLE:[node3]


really have no idea what does this means....