1) Is there any implication in running nodetool repair immediately after bringing a new node up (before key migration process is completed) ?
        Will it cause some race conditions ? Or will it result in some part of the space never be reclaimed ?
Repair will only be concerned with data that the node is replica for. And cleanup is only concerned with data that the node is no longer a replica for. 
AFAIK they should be able to run concurrently, but I would avoid it incase there are some edge cases. 

2) How can I figure out the status of key migration in Cassandra?
Not sure what you mean by key migration. 
If you are talking about a token move or node bootstrap you can get some idea from nodetool compactionstats and nodetool netstats. 

FWIW I think nodetool cleanup is less aggressive than repair. Repair reads all the data and creates a hash, cleanup just reads it from one file and writes a new file dropping rows that no longer belong. It's probably uses less CPU than compaction as it does not merge row fragments. 

Cheers

-----------------
Aaron Morton
Freelance Cassandra Consultant
New Zealand

@aaronmorton

On 19/06/2013, at 10:48 AM, Emalayan Vairavanathan <svemalayan@yahoo.com> wrote:

Thank you all.

I have two more question.

1) Is there any implication in running nodetool repair immediately after bringing a new node up (before key migration process is completed) ?
        Will it cause some race conditions ? Or will it result in some part of the space never be reclaimed ?

2) How can I figure out the status of key migration in Cassandra?

Thank you
Emalayan 


From: Richard Low <richard@wentnet.com>
To: user@cassandra.apache.org; Emalayan Vairavanathan <svemalayan@yahoo.com>
Sent: Tuesday, 18 June 2013 12:11 AM
Subject: Re: [Cassandra] Expanding a Cassandra cluster

On 10 June 2013 22:00, Emalayan Vairavanathan <svemalayan@yahoo.com> wrote:

                   b) Will Cassandra automatically take care of removing obsolete keys in future ?

In a future version Cassandra should automatically clean up for you:


Right now though you have to run cleanup eventually or the space will never be reclaimed.

Richard.