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https://issues.apache.org/jira/browse/SOLR-3939?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13483595#comment-13483595
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Yonik Seeley commented on SOLR-3939:
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Thinking of some scenarios where this could happen:
1. R1,R2 both up and active, add docs 1,2,3
2. bring R2 down
3. add docs 4 through 1million
4. bring R2 up, peersync fails, replication is kicked off
5. R2 finishes replication and becomes active, but it's recent version still
list 1,2,3
6. bring R1 down, R2 becomes the leader
7. bring R2 up, it does a peer-sync with R1, which looks like it has really old
versions (and succeeds because of that)
8. if the leader (R2) does a peer-sync back with R1, it will fail (not sure of
the consequences of this)
Another variation... if there's an update between 6 and 7:
6.5. add doc 1million+1
This will cause recent versions of R2 to be 1,2,3,1000001
It would be good to verify that peersync to the leader will either fail
(causing full replication), or pick up the new document.
> 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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