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https://issues.apache.org/jira/browse/SOLR-7989?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14989768#comment-14989768
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Ishan Chattopadhyaya commented on SOLR-7989:
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bq. Can we catch this in a unit test using the proxy jetties to simulate the
partitions?
Right, there's the DownLeaderTest. However, I don't think we should commit the
test. The test is quite a complex way of proving that there is a problem, and
that the problem is fixed once this patch goes in. But, it relies on LIR logic,
and if LIR code changes later, the test will have to keep up with that, which
is maintenance work. I couldn't find an easier way (apart from LIR) to trigger
this particular situation (down replica becoming leader, staying down).
> Down replica elected leader, stays down after successful election
> -----------------------------------------------------------------
>
> Key: SOLR-7989
> URL: https://issues.apache.org/jira/browse/SOLR-7989
> Project: Solr
> Issue Type: Bug
> Reporter: Ishan Chattopadhyaya
> Assignee: Noble Paul
> Attachments: DownLeaderTest.java, DownLeaderTest.java,
> SOLR-7989.patch, SOLR-7989.patch, SOLR-7989.patch, SOLR-7989.patch,
> SOLR-8233.patch
>
>
> It is possible that a down replica gets elected as a leader, and that it
> stays down after the election.
> Here's how I hit upon this:
> * There are 3 replicas: leader, notleader0, notleader1
> * Introduced network partition to isolate notleader0, notleader1 from leader
> (leader puts these two in LIR via zk).
> * Kill leader, remove partition. Now leader is dead, and both of notleader0
> and notleader1 are down. There is no leader.
> * Remove LIR znodes in zk.
> * Wait a while, and there happens a (flawed?) leader election.
> * Finally, the state is such that one of notleader0 or notleader1 (which were
> down before) become leader, but stays down.
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