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https://issues.apache.org/jira/browse/HBASE-12790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14388654#comment-14388654
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stack commented on HBASE-12790:
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So looking at the patch, a new concept -- 'grouping' -- is added to Scan as
public apis with no doc on what it is about.
Why is a grouping id a 'string'?
Does FairShareBalancedRPCExecutor add anything? Why in class comment does it
talk about scan when it plainly does nothing with scan. Ditto
FairShareRWQueueRPCExecutor.
So, simplerpcscheduler has defines for
53 public static final String CALL_QUEUE_GROUPING =
"hbase.ipc.server.callqueue.grouping";
54 public static final boolean CALL_QUEUE_GROUPING_DEFAULT_VALUE = false;
and other grouping pollution. Is this because you wanted to avoid putting in
place a fair scheduler implementation? Wouldn't it be cleaner doing this than
adding flags and conditional construction to simplerpcscheduler (its not a
simple scheduler anymore if it has fair scheduling stuff in it).
Back in a sec.
> 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
>
>
> 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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