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From "Erick Erickson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-6517) CollectionsAPI call REBALANCELEADERS
Date Wed, 29 Oct 2014 20:51:33 GMT

    [ https://issues.apache.org/jira/browse/SOLR-6517?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14188976#comment-14188976
] 

Erick Erickson commented on SOLR-6517:
--------------------------------------

bq: What happens to the node that is leader already?
nothing, it's already the leader, what purpose would be served by changing anything?

bq: What happens to other nodes in the queue?
Not sure what you're asking here. The trick is that if a replica has the preferredLeader property
set LeaderElector.joinElection is called with joinAtHead set to true. So it's next up in the
list when the leadership is changed. The rest of the nodes are still in the queue though,
ready to take over if the preferredLeader goes away.



> CollectionsAPI call REBALANCELEADERS
> ------------------------------------
>
>                 Key: SOLR-6517
>                 URL: https://issues.apache.org/jira/browse/SOLR-6517
>             Project: Solr
>          Issue Type: New Feature
>    Affects Versions: 5.0, Trunk
>            Reporter: Erick Erickson
>            Assignee: Erick Erickson
>             Fix For: 5.0, Trunk
>
>         Attachments: SOLR-6517.patch, SOLR-6517.patch, SOLR-6517.patch
>
>
> Perhaps the final piece of SOLR-6491. Once the preferred leadership roles are assigned,
there has to be a command "make it so Mr. Solr". This is something of a placeholder to collect
ideas. One wouldn't want to flood the system with hundreds of re-assignments at once. Should
this be synchronous or asnych? Should it make the best attempt but not worry about perfection?
Should it???
> a collection=name parameter would be required and it would re-elect all the leaders that
were on the 'wrong' node
> I'm thinking an optionally allowing one to specify a shard in the case where you wanted
to make a very specific change. Note that there's no need to specify a particular replica,
since there should be only a single preferredLeader per slice.
> This command would do nothing to any slice that did not have a replica with a preferredLeader
role. Likewise it would do nothing if the slice in question already had the leader role assigned
to the node with the preferredLeader role.



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