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From Anishek Agarwal <anis...@gmail.com>
Subject Re: Replication to second data center with different number of nodes
Date Mon, 30 Mar 2015 04:31:18 GMT
Colin,

When you said larger number of tokens has Query performance hit, is it read
or write performance. Also if you have any links you could share to shed
some light on this it would be great.

Thanks
Anishek

On Sun, Mar 29, 2015 at 2:20 AM, Colin Clark <colin@clark.ws> wrote:

> I typically use a # a lot lower than 256, usually less than 20 for
> num_tokens as a larger number has historically had a dramatic impact on
> query performance.
> —
> Colin Clark
> colin@clark.ws
> +1 612-859-6129
> skype colin.p.clark
>
> On Mar 28, 2015, at 3:46 PM, Eric Stevens <mightye@gmail.com> wrote:
>
> If you're curious about how Cassandra knows how to replicate data in the
> remote DC, it's the same as in the local DC, replication is independent in
> each, and you can even set a different replication strategy per keyspace
> per datacenter.  Nodes in each DC take up num_tokens positions on a ring,
> each partition key is mapped to a position on that ring, and whomever owns
> that part of the ring is the primary for that data.  Then (oversimplified)
> r-1 adjacent nodes become replicas for that same data.
>
> On Fri, Mar 27, 2015 at 6:55 AM, Sibbald, Charles <
> Charles.Sibbald@bskyb.com> wrote:
>
>>
>> http://www.datastax.com/documentation/cassandra/2.0/cassandra/configuration/configCassandra_yaml_r.html?scroll=reference_ds_qfg_n1r_1k__num_tokens
>>
>>  So go with a default 256, and leave initial token empty:
>>
>>  num_tokens: 256
>>
>> # initial_token:
>>
>>
>>  Cassandra will always give each node the same number of tokens, the
>> only time you might want to distribute this is if your instances are of
>> different sizing/capability which is also a bad scenario.
>>
>>   From: Björn Hachmann <bjoern.hachmann@metrigo.de>
>> Reply-To: "user@cassandra.apache.org" <user@cassandra.apache.org>
>> Date: Friday, 27 March 2015 12:11
>> To: user <user@cassandra.apache.org>
>> Subject: Re: Replication to second data center with different number of
>> nodes
>>
>>
>> 2015-03-27 11:58 GMT+01:00 Sibbald, Charles <Charles.Sibbald@bskyb.com>:
>>
>>> Cassandra’s Vnodes config
>>
>>
>> ​Thank you. Yes, we are using vnodes! The num_token parameter controls
>> the number of vnodes assigned to a specific node.​
>>
>>  Might be I am seeing problems where are none.
>>
>>  Let me rephrase my question: How does Cassandra know it has to
>> replicate 1/3 of all keys to each single node in the second DC? I can see
>> two ways:
>>  1. It has to be configured explicitly.
>>  2. It is derived from the number of nodes available in the data center
>> at the time `nodetool rebuild` is started.
>>
>>  Kind regards
>> Björn
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>
>
>

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