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

["Sam Overton (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-4123?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13402269#comment-13402269 ] 

Sam Overton edited comment on CASSANDRA-4123 at 6/27/12 2:52 PM:
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I should point out that the existing NTS (and also the modified implementation in CASSANDRA-3881) already prevent replicas from being placed on the same host. SimpleStrategy also is fixed in the CASSANDRA-4121 patch. The first couple of paragraphs in the ticket description could probably be removed.

The main issue left in this ticket is this notion of Distribution Factor and replica sets, to reduce the chance that simultaneous failures share data.


                
      was (Author: soverton):
    I should point out that the existing NTS (and also the modified implementation in CASSANDRA-3881) already prevent replicas from being placed on the same host. The first couple of paragraphs in the ticket description could probably be removed.

The main issue left in this ticket is this notion of Distribution Factor and replica sets, to reduce the chance that simultaneous failures share data.


                  
> 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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