Schema updates in cassandra tickle through the cluster over time very much like normal writes do. But they keep some state indicating the "parent" schema and they will only be applied to some node if the parent schema is correct thus asserting the correct order of schema changes. This process is subject to failure for instance because of nodes being down or network errors. If such a failure happens there it's still possible that everything is relatively easy fixed. Take down the node that missed the updates (use drain) and bring it back only. This might work (and does not take that long). If it does not take it down again (again drain) delete the data in the system keyspace. Bring it back online.
There is however a situation where you are really screwed. It is when you issue updates concurrently to different nodes. The schema versions will disagree and there is now possibility to bring them back to the same version again. In this case you need to select one node, bring down all nodes that have a different schema, delete their system keyspace and bring them back. Schema changes should not be seen as something that can be done regularly. It should not be done programmatically. There should always be some operator looking at the cluster verifying that all nodes are reachable and ring is ok. And then issue schema changes one at a time using the cli. Greetings, roland -----Ursprüngliche Nachricht----- Von: mcasandra [mailto:mohitanch...@gmail.com] Gesendet: Freitag, 15. April 2011 21:04 An: cassandra-u...@incubator.apache.org Betreff: Two versions of schema Is there a problem? [default@StressKeyspace] update column family StressStandard with keys_cached=100; 854ee0a0-6792-11e0-81f9-93d987913479 Waiting for schema agreement... The schema has not settled in 10 seconds; further migrations are ill-advised until it does. Versions are 854ee0a0-6792-11e0-81f9-93d987913479:[10.18.62.202, 10.18.62.203, 10.18.62.200, 10.18.62.204, 10.18.62.199, 10.18.62.196, 10.18.62.197],22d165ff-6783-11e0-81f9-93d987913479:[10.18.62.198] I remember reading somewhere before that when you have 2 versions of schemas you are basically in trouble. Can someone explain what it means and it's implications? -- View this message in context: http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/Two-versions-of-schema-tp6277365p6277365.html Sent from the cassandra-u...@incubator.apache.org mailing list archive at Nabble.com.
