[jira] [Commented] (CASSANDRA-4123) vnodes aware Replication Strategy

["Jonathan Ellis (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-4123?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13401659#comment-13401659 ] 

Jonathan Ellis commented on CASSANDRA-4123:
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bq. A better solution would be to add an extra level of hierarchy to NTS so that it still supported DC & rack, and IP would be the new level at the bottom of the hierarchy

Agreed--with the caveat that if we don't have enough racks to satisfy the replica count, we shrug and throw multiple replicas on a rack.  But if we don't have enough hosts, I think that should be fatal (as it is now, in the vnode-less world).
                
> vnodes aware Replication Strategy 
> ----------------------------------
>
>                 Key: CASSANDRA-4123
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4123
>             Project: Cassandra
>          Issue Type: Sub-task
>          Components: Core
>            Reporter: Sam Overton
>            Assignee: Sam Overton
>
> The simplest implementation for this would be if NTS regarded a single host as a distinct rack. This would prevent replicas being placed on the same host. The rest of the logic for replica selection would be identical to NTS (but this would be removing a level of topology hierarchy). This would be achievable just by writing a snitch to place hosts in their own rack.
> A better solution would be to add an extra level of hierarchy to NTS so that it still supported DC & rack, and IP would be the new level at the bottom of the hierarchy. The logic would remain largely the same.
> I would very much like to build in Peter Schuller's notion of Distribution Factor (as described in http://www.mail-archive.com/dev@cassandra.apache.org/msg03844.html). This requires a method of defining a "replica set" for each host and then treating it in a similar way to a DC (ie. RF replicas are chosen from that set, instead of from the whole cluster). 

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