> 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<mailto: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<http://twitter.com/#!/adforminsider> What is Adform: watch this short video<http://vimeo.com/adform/display> [Adform News] <http://www.adform.com> 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
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