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Date: Tue, 7 Mar 2017 10:34:38 +0000 (UTC)
From: "ramkrishna.s.vasudevan (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Commented] (HBASE-12790) Support fairness across
 parallelized scans
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archived-at: Tue, 07 Mar 2017 10:34:45 -0000


    [ https://issues.apache.org/jira/browse/HBASE-12790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15899197#comment-15899197 ] 

ramkrishna.s.vasudevan commented on HBASE-12790:
------------------------------------------------

Yes. This not only needs a pluggable RPC but also we should tag every scan request with a specifc id. That Id has to come from the client. HAving such an API to mark the scan opertion with an id but that id getting used only inside the RPC layer was the reason why this JIRA was not taken forward.

> 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_1.patch, HBASE-12790_5.patch, HBASE-12790_callwrapper.patch, HBASE-12790.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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