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From "Mark Miller (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-5872) Eliminate overseer queue
Date Mon, 17 Mar 2014 15:13:43 GMT

    [ https://issues.apache.org/jira/browse/SOLR-5872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13937901#comment-13937901
] 

Mark Miller commented on SOLR-5872:
-----------------------------------

I'm not fully sold on this yet. Compare and set is how this was first implemented and it has
it's own issues - hence the work Sami did to move to the queue. 

Potter has noticed the overseer is fairly slow at working through state updates. I think that
should be investigated first. 

> Eliminate overseer queue 
> -------------------------
>
>                 Key: SOLR-5872
>                 URL: https://issues.apache.org/jira/browse/SOLR-5872
>             Project: Solr
>          Issue Type: Improvement
>          Components: SolrCloud
>            Reporter: Noble Paul
>            Assignee: Noble Paul
>
> The overseer queue is one of the busiest points in the entire system. The raison d'ĂȘtre
of the queue is
>  * Provide batching of operations for the main clusterstate,json so that state updates
are minimized 
> * Avoid race conditions and ensure order
> Now , as we move the individual collection states out of the main clusterstate.json,
the batching is not useful anymore.
> Race conditions can easily be solved by using a compare and set in Zookeeper. 
> The proposed solution  is , whenever an operation is required to be performed on the
clusterstate, the same thread (and of course the same JVM)
>  # read the fresh state and version of zk node  
>  # construct the new state 
>  # perform a compare and set
>  # if compare and set fails go to step 1
> This should be limited to all operations performed on external collections because batching
would be required for others 



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