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From aaron morton <aa...@thelastpickle.com>
Subject Re: Cassandra in Multiple Datacenters Active - Standby configuration
Date Wed, 17 Aug 2011 09:20:55 GMT
The calculation for ownership does not understand the "multi ring" approach to assigning tokens.
I've created https://issues.apache.org/jira/browse/CASSANDRA-3047 for you. 

Otherwise your tokens look good to me. 

Cheers

-----------------
Aaron Morton
Freelance Cassandra Developer
@aaronmorton
http://www.thelastpickle.com

On 17/08/2011, at 9:19 AM, Oleg Tsvinev wrote:

> Hi all,
> 
> I followed instructions here:
> http://wiki.apache.org/cassandra/Operations#Token_selection
> to create a Cassandra cluster spanning two datacenters. Now I see that
> nodes belonging to DC2 datacenter own 0% of the ring. I would expect
> them to own 50%.
> 
> Does anyone have an idea what's going on here?
> 
> root@casper02:~# nodetool -h 10.4.64.63 ring
> Address         DC          Rack        Status State   Load
> Owns    Token
> 
>        85070591730234615865843651857942052865
> 10.4.64.63      DC1         RAC1        Up     Normal  36.19 MB
> 50.00%  0
> 10.4.65.55      DC2         RAC1        Up     Normal  36.21 MB
> 0.00%   1
> 10.4.65.73      DC1         RAC1        Up     Normal  530.12 KB
> 50.00%  85070591730234615865843651857942052864
> 10.4.64.166     DC2         RAC1        Up     Normal  525.68 KB
> 0.00%   85070591730234615865843651857942052865
> 
> Thank you,
>  Oleg
> 
> -------------
> 
> On Mon, Aug 15, 2011 at 1:39 PM, Oleg Tsvinev <oleg.tsvinev@gmail.com> wrote:
>> Hi all,
>> 
>> I have a question that documentation has not clear answer for. I have
>> the following requirements:
>> 
>> 1. Synchronously store data in datacenter DC1 on 2+ nodes
>> 2. Asynchronously replicate the same data to DC2 and store it on 2+
>> nodes to act as a hot standby
>> 
>> Now, I have configured keyspaces with o.a.c.l.NetworkTopologyStrategy
>> with strategy_options=[{DC1:2, DC2:2}] and use LOCAL_QUORUM
>> consistency level, following documentation here:
>> http://www.datastax.com/docs/0.8/operations/datacenter
>> 
>> Now, how do I assign initial tokens? If I have, say 6 nodes total, 3
>> in DC1 and 3 in DC2, and create a ring as if all 6 nodes share the
>> total 2^128 space equally.
>> Now say node N1:DC2 has key K and is in remote datacenter (for an app
>> in DC1). Wouldn't Cassandra always forward K to the DC2 node N1 thus
>> turning asynchronous writes into synchronous ones? Performance impact
>> will be huge as the latency between DC1 and DC2 is significant.
>> 
>> I hope there's an answer and I'm just missing something. My case falls
>> under Disaster Recovery in
>> http://www.datastax.com/docs/0.8/operations/datacenter but I don't see
>> how Cassandra will support my use case.
>> 
>> I appreciate any help on this.
>> 
>> Thank you,
>>  Oleg
>> 


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