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From Kauzki Aranami <kazuki.aran...@gmail.com>
Subject Re: About the replication strategy of Cassandra
Date Sat, 13 Mar 2010 22:38:47 GMT
>> Does each replication strategy of "Rack Unaware" "Rack Aware(within a
>> datacenter)" "Datacenter Aware" in Cassandra depend by the algorithm
>> adopted respectively?
>
> I still don't understand, sorry.



The description of the following document is quoted.



Cassandra provides various replication policies such as "Rack
Unaware", "Rack Aware" (within a datacenter) and "Datacenter Aware".
Replicas are chosen based on the replication policy chosen by the
application.

If certain application chooses "Rack Unaware" replication strategy
then the non-coordinator replicas are chosen by picking N-1 successors
of the coordinator on the ring. For "Rack Aware" and "Datacenter
Aware" strategies the algorithm is slightly more involved. Cassandra
system elects a leader amongst its nodes using a system called
Zookeeper.

Cassandra - A Decentralized Structured Storage System
http://www.cs.cornell.edu/projects/ladis2009/papers/lakshman-ladis2009.pdf



I want you to explain this "For "Rack Aware" and "Datacenter Aware"
strategies the algorithm is slightly more involved.". Is there an
algorithm corresponding to "Rack Aware" and "Datacenter Aware"? Can
Zookeeper be replaced?


> For ZK you should stick to one datacenter.  (you can still use
> RackAware for the, well, rack aware parts.)  ZK does multiple round
> trips for each write (think of it as 2pc) so it really does poorly
> across a wan.

ok, thanks!

-----------------------------------------------------------
  Kazuki Aranami

 Twitter: http://twitter.com/kimtea
 http://d.hatena.ne.jp/kazuki-aranami/
 -----------------------------------------------------------



2010/3/14 Jonathan Ellis <jbellis@gmail.com>:
> On Sat, Mar 13, 2010 at 3:47 PM, Kauzki Aranami
> <kazuki.aranami@gmail.com> wrote:
>> Does each replication strategy of "Rack Unaware" "Rack Aware(within a
>> datacenter)" "Datacenter Aware" in Cassandra depend by the algorithm
>> adopted respectively?
>
> I still don't understand, sorry.
>
>> For instance, what is the strategy recommended when Zookeeper is
>> adopted?A minimum speed of the line in the data center is anxious,
>> too.
>
> For ZK you should stick to one datacenter.  (you can still use
> RackAware for the, well, rack aware parts.)  ZK does multiple round
> trips for each write (think of it as 2pc) so it really does poorly
> across a wan.
>

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