Sharing my experience here. 1) Never had any issues with different size DCs. If the hardware is the same, keep the # to 256. 2) In most of the cases I keep the 256 vnodes and no performance problems (when they are triggered, the cause is not the vnodes #)
Regards, Carlos Juzarte Rolo Cassandra Consultant Pythian - Love your data rolo@pythian | Twitter: cjrolo | Linkedin: *linkedin.com/in/carlosjuzarterolo <http://linkedin.com/in/carlosjuzarterolo>* Tel: 1649 www.pythian.com On Mon, Mar 30, 2015 at 6:31 AM, Anishek Agarwal <[email protected]> wrote: > Colin, > > When you said larger number of tokens has Query performance hit, is it > read or write performance. Also if you have any links you could share to > shed some light on this it would be great. > > Thanks > Anishek > > On Sun, Mar 29, 2015 at 2:20 AM, Colin Clark <[email protected]> wrote: > >> I typically use a # a lot lower than 256, usually less than 20 for >> num_tokens as a larger number has historically had a dramatic impact on >> query performance. >> — >> Colin Clark >> [email protected] >> +1 612-859-6129 >> skype colin.p.clark >> >> On Mar 28, 2015, at 3:46 PM, Eric Stevens <[email protected]> wrote: >> >> If you're curious about how Cassandra knows how to replicate data in the >> remote DC, it's the same as in the local DC, replication is independent in >> each, and you can even set a different replication strategy per keyspace >> per datacenter. Nodes in each DC take up num_tokens positions on a ring, >> each partition key is mapped to a position on that ring, and whomever owns >> that part of the ring is the primary for that data. Then (oversimplified) >> r-1 adjacent nodes become replicas for that same data. >> >> On Fri, Mar 27, 2015 at 6:55 AM, Sibbald, Charles < >> [email protected]> wrote: >> >>> >>> http://www.datastax.com/documentation/cassandra/2.0/cassandra/configuration/configCassandra_yaml_r.html?scroll=reference_ds_qfg_n1r_1k__num_tokens >>> >>> So go with a default 256, and leave initial token empty: >>> >>> num_tokens: 256 >>> >>> # initial_token: >>> >>> >>> Cassandra will always give each node the same number of tokens, the >>> only time you might want to distribute this is if your instances are of >>> different sizing/capability which is also a bad scenario. >>> >>> From: Björn Hachmann <[email protected]> >>> Reply-To: "[email protected]" <[email protected]> >>> Date: Friday, 27 March 2015 12:11 >>> To: user <[email protected]> >>> Subject: Re: Replication to second data center with different number of >>> nodes >>> >>> >>> 2015-03-27 11:58 GMT+01:00 Sibbald, Charles <[email protected]>: >>> >>>> Cassandra’s Vnodes config >>> >>> >>> Thank you. Yes, we are using vnodes! The num_token parameter controls >>> the number of vnodes assigned to a specific node. >>> >>> Might be I am seeing problems where are none. >>> >>> Let me rephrase my question: How does Cassandra know it has to >>> replicate 1/3 of all keys to each single node in the second DC? I can see >>> two ways: >>> 1. It has to be configured explicitly. >>> 2. It is derived from the number of nodes available in the data center >>> at the time `nodetool rebuild` is started. >>> >>> Kind regards >>> Björn >>> Information in this email including any attachments may be >>> privileged, confidential and is intended exclusively for the addressee. The >>> views expressed may not be official policy, but the personal views of the >>> originator. If you have received it in error, please notify the sender by >>> return e-mail and delete it from your system. You should not reproduce, >>> distribute, store, retransmit, use or disclose its contents to anyone. >>> Please note we reserve the right to monitor all e-mail communication >>> through our internal and external networks. SKY and the SKY marks are >>> trademarks of Sky plc and Sky International AG and are used under licence. >>> Sky UK Limited (Registration No. 2906991), Sky-In-Home Service Limited >>> (Registration No. 2067075) and Sky Subscribers Services Limited >>> (Registration No. 2340150) are direct or indirect subsidiaries of Sky plc >>> (Registration No. 2247735). All of the companies mentioned in this >>> paragraph are incorporated in England and Wales and share the same >>> registered office at Grant Way, Isleworth, Middlesex TW7 5QD. >>> >> >> >> > -- --
