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From "Mark Miller (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-5615) Deadlock while trying to recover after a ZK session expiry
Date Tue, 07 Jan 2014 17:07:52 GMT

    [ https://issues.apache.org/jira/browse/SOLR-5615?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13864401#comment-13864401
] 

Mark Miller commented on SOLR-5615:
-----------------------------------

Thanks, perfect.

> Deadlock while trying to recover after a ZK session expiry
> ----------------------------------------------------------
>
>                 Key: SOLR-5615
>                 URL: https://issues.apache.org/jira/browse/SOLR-5615
>             Project: Solr
>          Issue Type: Bug
>          Components: SolrCloud
>    Affects Versions: 4.4, 4.5, 4.6
>            Reporter: Ramkumar Aiyengar
>         Attachments: SOLR-5615.patch
>
>
> The sequence of events which might trigger this is as follows:
>  - Leader of a shard, say OL, has a ZK expiry
>  - The new leader, NL, starts the election process
>  - NL, through Overseer, clears the current leader (OL) for the shard from the cluster
state
>  - OL reconnects to ZK, calls onReconnect from event thread (main-EventThread)
>  - OL marks itself down
>  - OL sets up watches for cluster state, and then retrieves it (with no leader for this
shard)
>  - NL, through Overseer, updates cluster state to mark itself leader for the shard
>  - OL tries to register itself as a replica, and waits till the cluster state is updated
>    with the new leader from event thread
>  - ZK sends a watch update to OL, but it is blocked on the event thread waiting for it.
> Oops. This finally breaks out after trying to register itself as replica times out after
20 mins.



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