[jira] [Commented] (SOLR-6760) New optimized DistributedQueue implementation for overseer

["Scott Blum (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SOLR-6760?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14680909#comment-14680909 ] 

Scott Blum commented on SOLR-6760:
----------------------------------

One big question I have is how to handle session/loss connection issues.  I worry that a hole in the patch I have is what happens if we lose ZK connection and regain it?  I have a feeling we'd end up in deadlock.  I think I need to add a general ConnectionStateListener so that I can mark having no watcher if we lose connection, and when connection comes back, tickle the notEmpty condition to cause all blocked threads to loop and ultimately refetch ZK state.

> New optimized DistributedQueue implementation for overseer
> ----------------------------------------------------------
>
>                 Key: SOLR-6760
>                 URL: https://issues.apache.org/jira/browse/SOLR-6760
>             Project: Solr
>          Issue Type: Bug
>            Reporter: Noble Paul
>            Assignee: Noble Paul
>         Attachments: SOLR-6760.patch
>
>
> Currently the DQ works as follows
> * read all items in the directory
> * sort them all 
> * take the head and return it and discard everything else
> * rinse and repeat
> This works well when we have only a handful of items in the Queue. If the items in the queue is much larger (in tens of thousands) , this is counterproductive
> As the overseer queue is a multiple producers + single consumer queue, We can read them all in bulk  and before processing each item , just do a zk.exists(itemname) and if all is well we don't need to do the fetch all + sort thing again



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