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 co...@clark.ws +1 612-859-6129 skype colin.p.clark
> On Mar 28, 2015, at 3:46 PM, Eric Stevens <migh...@gmail.com> 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 <charles.sibb...@bskyb.com > <mailto:charles.sibb...@bskyb.com>> wrote: > http://www.datastax.com/documentation/cassandra/2.0/cassandra/configuration/configCassandra_yaml_r.html?scroll=reference_ds_qfg_n1r_1k__num_tokens > > <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 <bjoern.hachm...@metrigo.de > <mailto:bjoern.hachm...@metrigo.de>> > Reply-To: "user@cassandra.apache.org <mailto:user@cassandra.apache.org>" > <user@cassandra.apache.org <mailto:user@cassandra.apache.org>> > Date: Friday, 27 March 2015 12:11 > To: user <user@cassandra.apache.org <mailto:user@cassandra.apache.org>> > Subject: Re: Replication to second data center with different number of nodes > > > 2015-03-27 11:58 GMT+01:00 Sibbald, Charles <charles.sibb...@bskyb.com > <mailto:charles.sibb...@bskyb.com>>: > 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. >
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