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From "Samarth Jain (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-12790) Support fairness across parallelized scans
Date Tue, 07 Mar 2017 06:42:32 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15898836#comment-15898836

Samarth Jain commented on HBASE-12790:

[~lhofhansl] - just having a pluggable RPCScheduler won't do it. Assuming we are targeting
only queries for now, we need to be able to tag/mark scans belonging to a query with the same
identifier. This information will be then used by the round robin queue to do the round-robin
of groups thing.
  public boolean dispatch(final CallRunner callTask) throws InterruptedException {

> 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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