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From Narendra Sharma <narendra.sha...@gmail.com>
Subject Re: network topology issue
Date Thu, 12 May 2011 00:49:34 GMT
My understanding is that the replication factor is for the entire ring. Even
if you have 2 DCs the nodes are part of the same ring. What you get
additionally from NTS is that you can specify how many replicas to place in
each DC.

So RF = 1 and DC1:1, DC2:1 looks incorrect to me.

What is possible with NTS is following:
RF=3, DC1=1, DC2=2

Would wait for others comments to see if my understand is correct.

-Naren

On Wed, May 11, 2011 at 5:41 PM, Anurag Gujral <anurag.gujral@gmail.com>wrote:

> Thanks Sameer for your answer.
> I am using two DCs DC1 , DC2 with both having one node each, my
> straegy_options values are DC1:1,DC2:1  I am not sure what my RF should be ,
> should it be 1 or 2?
> Please Advise
> Thanks
> Anurag
>
>
> On Wed, May 11, 2011 at 5:27 PM, Sameer Farooqui <cassandralabs@gmail.com>wrote:
>
>> Anurag,
>>
>> The Cassandra ring spans datacenters, so you can't use token 0 on both
>> nodes. Cassandra’s ring is from 0 to 2**127 in size.
>>
>> Try assigning one node the token of 0 and the second node 8.50705917 ×
>> 10^37 (input this as a single long number).
>>
>> To add a new keyspace in 0.8, run this from the CLI:
>> create keyspace KEYSPACENAME with placement_strategy =
>> org.apache.Cassandra.locator.NetworkTopologyStrategy' and strategy_options =
>> [{replication_factor:2}];
>>
>> If using 0.7, run "help create keyspace;" from the CLI and it'll show you
>> the correct syntax.
>>
>>
>> More info on tokens:
>>
>> http://journal.paul.querna.org/articles/2010/09/24/cassandra-token-selection/
>> <http://journal.paul.querna.org/articles/2010/09/24/cassandra-token-selection/>
>> http://wiki.apache.org/cassandra/Operations#Token_selection
>>
>>
>> On Wed, May 11, 2011 at 4:58 PM, Anurag Gujral <anurag.gujral@gmail.com>wrote:
>>
>>> Hi All,
>>>              I am testing network topology strategy in cassandra I am
>>> using two nodes , one node each in different data center.
>>> Since the nodes are in different dc I assigned token 0 to both the nodes.
>>> I added both the nodes as seeds in the cassandra.yaml and  I am  using
>>> properyfilesnitch as endpoint snitch where I have specified the colo
>>> details.
>>>
>>> I started first node then I when I restarted second node I got an error
>>> that token "0" is already being used.Why am I getting this error.
>>>
>>> Second Question: I already have cassandra running in two different data
>>> centers I want to add a new keyspace which uses networkTopology strategy
>>> in the light of above errors how can I accomplish this.
>>>
>>>
>>> Thanks
>>> Anurag
>>>
>>
>>
>


-- 
Narendra Sharma
Solution Architect
*http://www.persistentsys.com*
*http://narendrasharma.blogspot.com/*

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