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https://issues.apache.org/jira/browse/SOLR-3939?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13484652#comment-13484652
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Joel Bernstein commented on SOLR-3939:
--------------------------------------

I ran the Oct 14th test and the leader election worked perfectly. Then I tested 
shutting down the leader VM instead of unloading the loader core and this 
worked fine.  

Then I tried a leader with two replicas that had both just been replicated to. 
When I unloaded the leader neither replica became leader. But this was the case 
that was not yet accounted for I believe.

I can't think of a use case where the second scenario would happen though.

The first scenario though is critical for migrating micro-shards, so it's great 
that you committed this.

Thanks for your work on this issue.

Joel





                
> An empty or just replicated index cannot become the leader of a shard after a 
> leader goes down.
> -----------------------------------------------------------------------------------------------
>
>                 Key: SOLR-3939
>                 URL: https://issues.apache.org/jira/browse/SOLR-3939
>             Project: Solr
>          Issue Type: Bug
>          Components: SolrCloud
>    Affects Versions: 4.0-BETA, 4.0
>            Reporter: Joel Bernstein
>            Assignee: Mark Miller
>            Priority: Critical
>              Labels: 4.0.1_Candidate
>             Fix For: 4.1, 5.0
>
>         Attachments: cloud2.log, cloud.log, SOLR-3939.patch, SOLR-3939.patch
>
>
> When a leader core is unloaded using the core admin api, the followers in the 
> shard go into recovery but do not come out. Leader election doesn't take 
> place and the shard goes down.
> This effects the ability to move a micro-shard from one Solr instance to 
> another Solr instance.
> The problem does not occur 100% of the time but a large % of the time. 
> To setup a test, startup Solr Cloud with a single shard. Add cores to that 
> shard as replicas using core admin. Then unload the leader core using core 
> admin. 

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