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https://issues.apache.org/jira/browse/SOLR-5872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13938717#comment-13938717
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Noble Paul commented on SOLR-5872:
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bq.I'm not really fully up on "external collections" but AFAIK it's part of
some other work to support tons of collections
There is more and more information getting added to the cluster state . I'm
sure no one would object to the point that splitting the clusterstate.json
would be a more scalable solution and the right direction to take. Of course,
this is not to be done in haste , but eventually that should be the way. The
eventual goal should be to support very large no:of collections (say 1000's)
and support extremely large collections (with 1000's of slices) . Solr itself
will not have any problem scaling like that but the Overseer/clusterstate
strategy will go through a revamp before we reach there.
> 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'être 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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