[jira] [Commented] (HELIX-272) Provide a mechanism to prevent particular states for a partition to be colocated

["kishore gopalakrishna (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HELIX-272?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13795725#comment-13795725 ] 

kishore gopalakrishna commented on HELIX-272:
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The default rebalancing algorithm in Helix already takes care of this. All replicas of a partition are assigned to different instances. But a physical node can have multiple instances which is not taken into account currently.


> Provide a mechanism to prevent particular states for a partition to be colocated
> --------------------------------------------------------------------------------
>
>                 Key: HELIX-272
>                 URL: https://issues.apache.org/jira/browse/HELIX-272
>             Project: Apache Helix
>          Issue Type: Improvement
>            Reporter: Matthieu Morel
>
> For instance, (for a given partition) we have a master writer and a warm backup that reads from a journal and applies updates. 
> If the node hosting the master dies, the warm backup would take over quickly because it would have to read and apply only few updates from the journal.
> However, if both the master writer and the warm backup are colocated, this does not work.
> Thus it would be good to be able to specify exclusion rules. E.g. prevent some states of a given partition to be colocated, or provide thresholds.



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