ReadRepair means including all UP replicas in the request, waiting
asynchronously after the read has completed, resolving and repairing
differences. If you read at QUOURM with RR running, ALL (replace) nodes will
perform a read.
At any CL > ONE the responses from CL nodes are reconciled and differences are
repaired using a mechanism similar to RR. This has to happen before the
response can be sent to the client.
The naming does not help, but they are a different. RR is a background process
designed to reduce the chance of an inconsistent read. It's needed less since
changed to Hinted Handoff in 1.0.
Cheers
-----------------
Aaron Morton
Freelance Developer
@aaronmorton
http://www.thelastpickle.com
On 24/05/2012, at 5:47 AM, Daning Wang wrote:
> 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.jevdoki...@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.
>
>
>
>
>
>
>
> Best regards / Pagarbiai
> Viktor Jevdokimov
> Senior Developer
>
> Email: viktor.jevdoki...@adform.com
> Phone: +370 5 212 3063, Fax +370 5 261 0453
> J. Jasinskio 16C, LT-01112 Vilnius, Lithuania
> Follow us on Twitter: @adforminsider
> What is Adform: watch this short video
> <signature-logo7789.png>
>
> Disclaimer: The information contained in this message and attachments is
> intended solely for the attention and use of the named addressee and may be
> confidential. If you are not the intended recipient, you are reminded that
> the information remains the property of the sender. You must not use,
> disclose, distribute, copy, print or rely on this e-mail. If you have
> received this message in error, please contact the sender immediately and
> irrevocably delete this message and any copies.
>
> From: aaron morton [mailto:aa...@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
>
>
>
>
