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From Yudong Gao <st...@umich.edu>
Subject Re: Update the Keyspace replication factor online
Date Wed, 13 Apr 2011 04:00:32 GMT
Thanks for the reply, Aaron!

On Tue, Apr 12, 2011 at 10:52 PM, aaron morton <aaron@thelastpickle.com> wrote:
> Are you changing the replication factor or moving nodes ?

I am just changing the replication factor, without touching the node
configuration.

>
> To change the RF you need to repair and then once all repairing is done run cleanup to
remove the hold data.

Do I need to shutdown the cluster when running the repair? If I just
repair the nodes one by one, will some users get the error of no data
exists, if the node responsible for the new replica is not yet
repaired?

Yudong

>
> You can move whole nodes by moving all their data with them, assigning a new ip, and
updating the topology file if used.
>
> Aaron
>
> On 13 Apr 2011, at 07:56, Yudong Gao wrote:
>
>> Hi,
>>
>> What operations will be executed (and what is the associated overhead)
>> when the Keyspace replication factor is changed online, in a
>> multi-datacenter setup with NetworkTopologyStrategy?
>>
>> I checked the wiki and the archive of the mailing list and find this,
>> but it is not very complete.
>>
>> http://wiki.apache.org/cassandra/Operations
>> "
>> Replication factor is not really intended to be changed in a live
>> cluster either, but increasing it may be done if you (a) use
>> ConsistencyLevel.QUORUM or ALL (depending on your existing replication
>> factor) to make sure that a replica that actually has the data is
>> consulted, (b) are willing to accept downtime while anti-entropy
>> repair runs (see below), or (c) are willing to live with some clients
>> potentially being told no data exists if they read from the new
>> replica location(s) until repair is done.
>> "
>>
>> More specifically, in this scenario:
>>
>> {DC1:1, DC2:1} -> {DC2:1, DC3:1}
>>
>> 1. Can this be done online without shutting down the cluster? I
>> thought there is an "update keyspace" command in the cassandra-cli.
>>
>> 2. If so, what operations will be executed? Will new replicas be
>> created in new locations (in DC3) and existing replicas be deleted in
>> old locations (in DC1)?
>>
>> 3. Or they will be updated only with read with ConssitencyLevel.QUORUM
>> or All, or "nodetool repair"?
>>
>> Thanks!
>>
>> Yudong
>
>

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