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From Edward Capriolo <edlinuxg...@gmail.com>
Subject Re: In a multiple data center setup, do all the data centers have complete data irrespective of RF?
Date Mon, 20 May 2013 21:45:35 GMT
Replication factor USED to be a property of the keyspace. Now as you can
see it is correctly associated with strategy options. This makes sense
because the strategy uses the options to decide how any where to place data.


On Mon, May 20, 2013 at 1:46 PM, Bryan Talbot <btalbot@aeriagames.com>wrote:

> On Mon, May 20, 2013 at 10:01 AM, Pinak Pani <
> nishant.has.a.question@gmail.com> wrote:
>
>> Assume NetworkTopologyStrategy. So, I wanted to know whether a
>> data-center will contain all the keys?
>>
>> This is the case:
>>
>> CREATE KEYSPACE appKS
>>   WITH placement_strategy = 'NetworkTopologyStrategy'
>>   AND strategy_options={DC1:3, DC2:3};
>>
>> Does DC1 and DC2 each contain complete database corpus? That is, if DC1
>> blows, will I get all the data from DC2? Assume RF = 1.
>>
>
>
> Your config sample isn't RF=1 it's RF=3.  That's what the DC1:3 and DC2:3
> mean -- set RF=3 for DC1 and RF=3 for DC2 for all rows of all CFs in this
> keyspace.
>
>
>
>
>
>>
>> Sorry, for the very elementary question. This is the post that made me
>> ask this question:
>> http://www.onsip.com/blog/2011/07/15/intro-to-cassandra-and-networktopologystrategy
>>
>> It says,
>>
>> "NTS creates an iterator for EACH datacenter and places writes discretely
>> for each. The result is that NTS basically breaks each datacenter into it's
>> own logical ring when it places writes."
>>
>
> A lot of things change in fast moving projects in 2 years, so you'll have
> to take anything written 2 years ago with a grain of salt and figure out if
> it's still true with whatever version you're using.
>
>
>
>
>>
>> That seems to mean that each data-center behaves as an independent ring
>> with initial_token. So, If I have 2 data centers and NTS, I am basically
>> mirroring the database. Right?
>>
>>
>
> Depending on how you've configured your placement strategy, but if you're
> using DC1:3 and DC2:3 like you have above, then yes, you'd expect to have 3
> copies of every row in both data centers for that keyspace.
>
> -Bryan
>
>

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