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From Viktor Jevdokimov <Viktor.Jevdoki...@adform.com>
Subject RE: Replication factor
Date Wed, 23 May 2012 10:51:14 GMT
> 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.




Best regards / Pagarbiai
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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