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https://issues.apache.org/jira/browse/SOLR-6491?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14134975#comment-14134975
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Erick Erickson commented on SOLR-6491:
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[~noble.paul] right, but AFAIK, the Overseer stuff isn't particularly sensitive
to collections and shards. Is there a notion of assigning an overseer role for
a particular node but _only_ for a particular collection/shard combination? All
you've got is the role and the node, I don't see any way to say "add a role for
_this_ collection and _this_ shard.
Of course if there is a way I've just wasted a bunch of time.
[~shalinmangar] I'm trusting some folks who are reporting the edge case, hoping
they'll chime in with "real world". But even if not, "an extra thread or two"
times 100 shards can mount up.
> Add preferredLeader as a ROLE and a collections API command to respect this
> role
> --------------------------------------------------------------------------------
>
> Key: SOLR-6491
> URL: https://issues.apache.org/jira/browse/SOLR-6491
> Project: Solr
> Issue Type: Improvement
> Affects Versions: 4.11, 5.0
> Reporter: Erick Erickson
> Assignee: Erick Erickson
>
> Leaders can currently get out of balance due to the sequence of how nodes are
> brought up in a cluster. For very good reasons shard leadership cannot be
> permanently assigned.
> However, it seems reasonable that a sys admin could optionally specify that a
> particular node be the _preferred_ leader for a particular collection/shard.
> During leader election, preference would be given to any node so marked when
> electing any leader.
> So the proposal here is to add another role for preferredLeader to the
> collections API, something like
> ADDROLE?role=preferredLeader&collection=collection_name&shard=shardId
> Second, it would be good to have a new collections API call like
> ELECTPREFERREDLEADERS?collection=collection_name
> (I really hate that name so far, but you see the idea). That command would
> (asynchronously?) make an attempt to transfer leadership for each shard in a
> collection to the leader labeled as the preferred leader by the new ADDROLE
> role.
> I'm going to start working on this, any suggestions welcome!
> This will subsume several other JIRAs, I'll link them momentarily.
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