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From "Erick Erickson (JIRA)" <>
Subject [jira] [Commented] (SOLR-6517) CollectionsAPI call REBALANCELEADERS
Date Mon, 03 Nov 2014 15:43:34 GMT


Erick Erickson commented on SOLR-6517:

Well, it's worked in every test, both manual and automated that I've run so far. Do you have
a failure that demonstrates this?

Maybe a mismatch in expectations? REBALANCELEADERS does _not_, and was not designed to, force
the rebalancing immediately for nodes that do not have the preferredLeader property already
set. It simply makes leaders out of those nodes that _already_ have the preferredLeader property
set and are not currently the leader.

So to rebalance the leaders across the cluster, you first need to BALANCESHARDUNIQUE with
the preferredLeader property and _then_ issue the REBALANCELEADERS command. That way it's
not required that the entire cluster be balanced, you can selectively assign _some_ preferredLeaders
if you want.

Or am I missing the boat completely? How do you see it "not working"?

> ------------------------------------
>                 Key: SOLR-6517
>                 URL:
>             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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