Re: NetworkTopologyStrategy and nodes ?

2013-10-17 Thread Tyler Hobbs 
On Sat, Oct 12, 2013 at 9:08 AM, Andrew Cobley a.e.cob...@dundee.ac.ukwrote:


  In the following graphic, notice the tokens are assigned to alternating
 racks. For more information, see *Generating 
 Tokens*http://www.datastax.com/docs/1.1/initialize/token_generation#token-gen-cassandra
 .

  Seems to imply that the strategy relies on placing tokens on different
 racks which won't happen with nodes ?


Right, you won't be able to control whether neighboring tokens have
alternating racks with vnodes.

The main reason that they should be alternating without vnodes is to avoid
a large imbalance in ring ownership.  Without vnodes, if a node owns just
one extra range, it will make a big difference because each range is quite
large.

With vnodes, this is much less of a concern.  You still have a lot of
imbalances, but they are each fairly small and in aggregate they mostly
cancel each other out.

-- 
Tyler Hobbs
DataStax http://datastax.com/

NetworkTopologyStrategy and nodes ?

2013-10-12 Thread Andrew Cobley 
Reading this explanation of NetworkTopologyStrategy  in 1.1:

http://www.datastax.com/docs/1.1/cluster_architecture/replication

Is there a suitable explanation of how it will work with Vnodes ?  I notice 
this line in the explanation:

In the following graphic, notice the tokens are assigned to alternating racks. 
For more information, see Generating 
Tokenshttp://www.datastax.com/docs/1.1/initialize/token_generation#token-gen-cassandra.

Seems to imply that the strategy relies on placing tokens on different racks 
which won't happen with nodes ?

Regards
Andy C


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