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https://issues.apache.org/jira/browse/SOLR-6491?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14134954#comment-14134954
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Shalin Shekhar Mangar commented on SOLR-6491:
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bq. Since updates do put some extra load on the leader, this can create an odd
load distribution.
What's the extra load? Every replica writes to the transaction log and the
index. The leader has an extra thread or two to write updates to replicas but
that is it. I don't see why that should be expensive or create undue load.
We've had bugs in the past such as SOLR-6136 but if there are others then we
should find those and fix them before we go through with this feature.
> 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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