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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-12790) Support fairness across parallelized scans
Date Tue, 31 Mar 2015 15:48:53 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14388730#comment-14388730

stack commented on HBASE-12790:

I see the new queue implementation doing a bunch of extra work while the q lock is held. Any
micro-benchmark compare of this implementation to current q implementation even with no grouping

Is a 'producer' a 'group'? (Odd having method named extractProducer return group).

Why only 'scans' implemented? Wouldn't we want fairness for any method invoked against the

Do you have any proof this code delivers what is suggested at the top of this issue, that
if all cilent A's scans are queued before all of client B's, that client B will get some action.

So, users would have to 'enable' this on the cluster? It would not be on by default?  If no
degradation in scheduler, why would we not want this always on (if it indeed does fairness)?

> 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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