Hi Aaron,
              Thanks for your mail. I am leaning towards making a new cluster since I am using cassandra version
0.7.3 and the fix you have put in is in cassandra 0.7.5, and I am less adventurous primarily because it is live system and service disruption is not what is desirable.

I have two more questions for you:

a)Is there a way to specify snitch in cassandra per CF rather than one snitch for all column family.

b)I have a weird issue with 0.7.3 when using property file snitch and a new node is added to an existing running
cassandra cluster(which uses property file snitch) I have to add new node's IP to the cassandra-topology.properties of all the existing  cassandra nodes otherwise the new node gives error
ERROR [main] 2011-05-13 23:41:30,821 AbstractCassandraDaemon.java (line 333) Exception encountered during startup.
java.lang.NullPointerException
    at org.apache.cassandra.locator.PropertyFileSnitch.getDatacenter(PropertyFileSnitch.java:96)
    at org.apache.cassandra.locator.NetworkTopologyStrategy.calculateNaturalEndpoints(NetworkTopologyStrategy.java:87)
    at org.apache.cassandra.locator.AbstractReplicationStrategy.getAddressRanges(AbstractReplicationStrategy.java:196)
    at org.apache.cassandra.locator.AbstractReplicationStrategy.getPendingAddressRanges(AbstractReplicationStrategy.java:230)
    at org.apache.cassandra.dht.BootStrapper.getRangesWithSources(BootStrapper.java:195)
    at org.apache.cassandra.dht.BootStrapper.bootstrap(BootStrapper.java:83)
    at org.apache.cassandra.service.StorageService.bootstrap(StorageService.java:525)
    at org.apache.cassandra.service.StorageService.joinTokenRing(StorageService.java:453)
    at org.apache.cassandra.service.StorageService.initServer(StorageService.java:403)
    at org.apache.cassandra.service.AbstractCassandraDaemon.setup(AbstractCassandraDaemon.java:194)
    at org.apache.cassandra.service.AbstractCassandraDaemon.activate(AbstractCassandraDaemon.java:316)
    at org.apache.cassandra.thrift.CassandraDaemon.main(CassandraDaemon.java:79)
java.lang.NullPointerException
    at org.apache.cassandra.locator.PropertyFileSnitch.getDatacenter(PropertyFileSnitch.java:96)
    at org.apache.cassandra.locator.NetworkTopologyStrategy.calculateNaturalEndpoints(NetworkTopologyStrategy.java:87)
    at org.apache.cassandra.locator.AbstractReplicationStrategy.getAddressRanges(AbstractReplicationStrategy.java:196)
    at org.apache.cassandra.locator.AbstractReplicationStrategy.getPendingAddressRanges(AbstractReplicationStrategy.java:230)
    at org.apache.cassandra.dht.BootStrapper.getRangesWithSources(BootStrapper.java:195)
    at org.apache.cassandra.dht.BootStrapper.bootstrap(BootStrapper.java:83)
    at org.apache.cassandra.service.StorageService.bootstrap(StorageService.java:525)
    at org.apache.cassandra.service.StorageService.joinTokenRing(StorageService.java:453)
    at org.apache.cassandra.service.StorageService.initServer(StorageService.java:403)
    at org.apache.cassandra.service.AbstractCassandraDaemon.setup(AbstractCassandraDaemon.java:194)
    at org.apache.cassandra.service.AbstractCassandraDaemon.activate(AbstractCassandraDaemon.java:316)
    at org.apache.cassandra.thrift.CassandraDaemon.main(CassandraDaemon.java:79)

Thanks for all your help.

Anurag


On Sun, May 15, 2011 at 3:56 PM, aaron morton <aaron@thelastpickle.com> wrote:
Rename a cluster 
http://wiki.apache.org/cassandra/FAQ#clustername_mismatch
see also https://issues.apache.org/jira/browse/CASSANDRA-2632

The best approach will depend on 
- how much data you have
- if this is a running system 
- are the schemas identical 
- are the individual clusters using the NetworkTopologyStrategy ? 
- how much excitement you like.  

Initial thoughts, doubt this is correct...

- change the tokens in each dc 
- for a dc that will have the others join it, change cassandra-topology.properties to put the new nodes in the new dc
- for a dc joining another, follow the procedure to change the name on each node, update the seed list and update the topology to include the dc it is joining, remove the schema and migrations SStables, as you do a rolling restart
- update the seed list on the dc the others joined
- confirm there is one schema def
- update the replication factor of the schema to put replicas in each DC  http://wiki.apache.org/cassandra/Operations#Replication
- nodetool repair to change the RF and then cleanup 

There will be a lot of data moves and I doubt I got it right, is there any chance of spinning up a whole new cluster and reloading the data ?

I can give it some more thought later if you need. 

Hope that helps. 

-----------------
Aaron Morton
Freelance Cassandra Developer
@aaronmorton

On 14 May 2011, at 04:55, Anurag Gujral wrote:

Hi All,
            I  have 3 separate cassandra clusters running in multiple data centers which I want to convert to  one cassandra cluster across multiple data centers
Does anyone tried this? If so what are the steps:

I think I need to do the following:
a)Change cluster name: What is the procedure to do this?
b)Change tokens so that each node have a unique token
c)Change seed nodes so that machines in one data center know about machines in another data center.

Thanks
Anurag