[jira] [Resolved] (SOLR-6790) Implement a leader-serves-reads flag

["Timothy Potter (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SOLR-6790?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Timothy Potter resolved SOLR-6790.
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    Resolution: Won't Fix

See last comment - turns out there is more load on the replica than on the leader due to how batching from leader to replica works.

> Implement a leader-serves-reads flag
> ------------------------------------
>
>                 Key: SOLR-6790
>                 URL: https://issues.apache.org/jira/browse/SOLR-6790
>             Project: Solr
>          Issue Type: New Feature
>          Components: SolrCloud
>            Reporter: Timothy Potter
>
> ZooKeeper has a flag that allows you to disable leaders serving reads, from some basic indexing performance analysis, leaders have visibly higher CPU and heap usage. Here are some screen shots that show the difference between a leader and replica in a 1x2 collection with no query activity (just indexing):
> leader - http://www.dropmocks.com/mHoPUx
> replica - http://www.dropmocks.com/mHoWpX
> There's a clear difference in peak & avg CPU and heap usage. I'm guessing the difference would be even more pronounced if there were more replicas involved.
> Setting the leader-serves-reads=false allows the leader to only do indexing and serve no queries so long as there are other active replicas. I'm thinking this will be true by default but able to set to false per collection. Of course if only the leader is up, then it will serve reads.



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