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Date: Sun, 13 Oct 2013 22:17:52 -0700
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Subject: Re: Regarding QoS for Handlers
From: Devaraj Das <ddas@hortonworks.com>
To: "dev@hbase.apache.org" <dev@hbase.apache.org>
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Varun, it'll be good to have your inputs on HBASE-8836 which I think is
related to what you are talking about.


On Sun, Oct 13, 2013 at 1:54 PM, Varun Sharma <varun@pinterest.com> wrote:

> Or a slightly alternative approach would be to have a CallQueue
> implementation which is more of a priorityQueue.
>
> The Queue wrapper has a number of different queues [TableName:RpcName]
> sorted in descending order by priority level and finally the default quue.
> Dequeue on this queue shall go in descending order of priority.
>
> Varun
>
>
> On Sun, Oct 13, 2013 at 1:36 PM, Varun Sharma <varun@pinterest.com> wrote:
>
> > Hi,
> >
> > I am wondering if QoS on handler threads is being looked at by someone ?
> > We have found huge gains by doing this for asymmetric workloads which are
> > extremely write heavy but latency on reads matters the most. Basically we
> > forked out a separate thread pool of X threads for handling reads to
> > prevent starvation of read requests which were far outnumbered by the #
> of
> > writes.
> >
> > As of now, we have been making adhoc changes (like introduce higher
> > priority levels for certain types of requests like gets and scans) but
> > having a framework to control this would be a really nice thing.
> >
> > One simple way to achieve this would be to have a group of "high priority
> > handler threads" and be able to mark each table to prioritize
> > "reads/writes". On receiving an RPC, the request is directly dispatched
> to
> > this other pool of threads and the remaining RPCs go to the regular pool.
> > This would be a naive implementation.
> >
> > The issue with this could be that what happens when the user ends up
> > directing most of their load to the high priority pool which has fewer
> > threads. We could do something simple like having a tight upper bound on
> > the call queue length and if a new high priority call is rejected from
> this
> > pool, just enqueue it to the regular pool of requests.
> >
> > Thoughts ?
> >
> > Thanks !
> > Varun
> >
>

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