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From Daning Wang <dan...@netseer.com>
Subject Re: Replication factor
Date Wed, 23 May 2012 17:47:01 GMT
Thanks guys.

Aaron, I am confused about this. from wiki
http://wiki.apache.org/cassandra/ReadRepair, looks for any consistency
level. Read Repair will be done either before or after responding data.

  >Read Repair does not run at CL ONE

Daning

On Wed, May 23, 2012 at 3:51 AM, Viktor Jevdokimov <
Viktor.Jevdokimov@adform.com> wrote:

>  > When RF == number of nodes, and you read at CL ONE you will always be
> reading locally.****
>
> “always be reading locally” – only if Dynamic Snitch is “off”. With
> dynamic snitch “on” request may be redirected to other node, which may
> introduce latency spikes.****
>
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> *Viktor Jevdokimov*
> Senior Developer
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>   *From:* aaron morton [mailto:aaron@thelastpickle.com]
> *Sent:* Wednesday, May 23, 2012 13:00
> *To:* user@cassandra.apache.org
> *Subject:* Re: Replication factor****
>
> ** **
>
> RF is normally adjusted to modify availability (see
> http://thelastpickle.com/2011/06/13/Down-For-Me/)****
>
> ** **
>
> for example, if I have 4 nodes cluster in one data center, how can RF=2 vs
> RF=4 affect read performance? If consistency level is ONE, looks reading
> does not need to go to another hop to get data if RF=4, but it would do
> more work on read repair in the background.****
>
>  Read Repair does not run at CL ONE.****
>
> When RF == number of nodes, and you read at CL ONE you will always be
> reading locally. But with a low consistency.****
>
> If you read with QUORUM when RF == number of nodes you will still get some
> performance benefit from the data being read locally.****
>
> ** **
>
> Cheers****
>
> ** **
>
> ** **
>
> -----------------****
>
> Aaron Morton****
>
> Freelance Developer****
>
> @aaronmorton****
>
> http://www.thelastpickle.com****
>
> ** **
>
> On 23/05/2012, at 9:34 AM, Daning Wang wrote:****
>
>
>
> ****
>
> Hello,
>
> What is the pros and cons to choose different number of replication factor
> in term of performance? if space is not a concern.
>
> for example, if I have 4 nodes cluster in one data center, how can RF=2 vs
> RF=4 affect read performance? If consistency level is ONE, looks reading
> does not need to go to another hop to get data if RF=4, but it would do
> more work on read repair in the background.
>
> Can you share some insights about this?
>
> Thanks in advance,
>
> Daning ****
>
> ** **
>

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