Hi All,

Datastax manual suggests that during a Cassandra cluster expansion, an 
administrator has to run nodetool cleanup on each of the previously existing 
Cassandra nodes to remove the keys that are no longer belonging to those nodes. 
Further the manual says that thenodetool cleanup  task should be run 
sequentially on the existing Cassandra nodes.

Reference: 
http://www.datastax.com/docs/1.2/operations/add_replace_nodes#adding-capacity

Here is my problem: I have a very large Cassandra cluster with 100s of nodes 
and running nodetool cleanup sequentially will take a long time to finish. 

 Questions: a) So can someone tell me  about the implications of running the 
nodetool cleanup concurrently on the entire cluster ?
                   b) Will Cassandra automatically take care of removing 
obsolete keys in future ?


Thank you
Emalayan 

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