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From "dafu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HELIX-50) Ensure num replicas and preference list size in idealstate matches
Date Thu, 21 Feb 2013 00:15:12 GMT

    [ https://issues.apache.org/jira/browse/HELIX-50?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13582704#comment-13582704

dafu commented on HELIX-50:

restate the problem here.

replica: 2 (which should be 3)
preference-list: "node_0, node_1, node_2"

node_1: slave
node_2: slave

so the best-possible-state will be:
node_0: master
node_1: slave

but since replica is set to 2, we can't bring any instance (node_0 here) to slave state. and
thus helix keep two slave state (but no master state) for the partition. 

we need 2 fixes here:
1) validate ideal-state
2) when generate/select message, we take into consideration the state priority, so we should
send offline->slave messages to instances (e.g. node_0) whose desire state (e.g. master)
has a higher priority.

> Ensure num replicas and preference list size in idealstate matches
> ------------------------------------------------------------------
>                 Key: HELIX-50
>                 URL: https://issues.apache.org/jira/browse/HELIX-50
>             Project: Apache Helix
>          Issue Type: Bug
>            Reporter: kishore gopalakrishna
> Currently we dont validate that the number of replicas and size of preference list is
the same. This results in inconsistent behaviour.

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