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https://issues.apache.org/jira/browse/HBASE-12790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14989995#comment-14989995
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ramkrishna.s.vasudevan commented on HBASE-12790:
------------------------------------------------

There are few things to check here. Once Phoenix allows this type of factory 
and since this is an external entity adding to hbase's scheduling - then the 
executors to be used with Replication, the type of queues like fifo, deadline 
everything needs to be handled. 
So if HBase adds some new type of Executor all that needs to be included and as 
Andrew said maintenance will be a tougher. 

> Support fairness across parallelized scans
> ------------------------------------------
>
>                 Key: HBASE-12790
>                 URL: https://issues.apache.org/jira/browse/HBASE-12790
>             Project: HBase
>          Issue Type: New Feature
>            Reporter: James Taylor
>            Assignee: ramkrishna.s.vasudevan
>              Labels: Phoenix
>         Attachments: AbstractRoundRobinQueue.java, HBASE-12790.patch, 
> HBASE-12790_1.patch, HBASE-12790_5.patch, HBASE-12790_callwrapper.patch, 
> HBASE-12790_trunk_1.patch, PHOENIX_4.5.3-HBase-0.98-2317-SNAPSHOT.zip
>
>
> Some HBase clients parallelize the execution of a scan to reduce latency in 
> getting back results. This can lead to starvation with a loaded cluster and 
> interleaved scans, since the RPC queue will be ordered and processed on a 
> FIFO basis. For example, if there are two clients, A & B that submit largish 
> scans at the same time. Say each scan is broken down into 100 scans by the 
> client (broken down into equal depth chunks along the row key), and the 100 
> scans of client A are queued first, followed immediately by the 100 scans of 
> client B. In this case, client B will be starved out of getting any results 
> back until the scans for client A complete.
> One solution to this is to use the attached AbstractRoundRobinQueue instead 
> of the standard FIFO queue. The queue to be used could be (maybe it already 
> is) configurable based on a new config parameter. Using this queue would 
> require the client to have the same identifier for all of the 100 parallel 
> scans that represent a single logical scan from the clients point of view. 
> With this information, the round robin queue would pick off a task from the 
> queue in a round robin fashion (instead of a strictly FIFO manner) to prevent 
> starvation over interleaved parallelized scans.



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