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Kafka, mail # user - Consumer throughput imbalance


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Ian Friedman 2013-08-24, 16:59
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Neha Narkhede 2013-08-25, 14:46
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Ian Friedman 2013-08-25, 16:01
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Mark 2013-08-25, 16:14
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Ian Friedman 2013-08-25, 17:17
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Ian Friedman 2013-08-25, 17:24
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Jay Kreps 2013-08-25, 19:12
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Ian Friedman 2013-08-26, 05:02
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Re: Consumer throughput imbalance
Jay Kreps 2013-08-26, 17:27
Yeah it is always equal to the fetch size. The fetch size needs to be at
least equal to the max message size you have allowed on the server, though.

-Jay
On Sun, Aug 25, 2013 at 10:00 PM, Ian Friedman <[EMAIL PROTECTED]> wrote:

> Jay - is there any way to control the size of the interleaved chunks? The
> performance hit would likely be negligible for us at the moment.
>
> --
> Ian Friedman
>
>
> On Sunday, August 25, 2013 at 3:11 PM, Jay Kreps wrote:
>
> > I'm still a little confused by your description of the problem. It might
> be
> > easier to understand if you listed out the exact things you have
> measured,
> > what you saw, and what you expected to see.
> >
> > Since you mentioned the consumer I can give a little info on how that
> > works. The consumer consumes from all the partitions it owns
> > simultaneously. The behavior is that we interleve fetched data chunks of
> > messages from each partition the consumer is processing. The chunk size
> is
> > controlled by the fetch size set in the consumer. So the behavior you
> would
> > expect is that you would get a bunch of messages from one partition
> > followed by a bunch from another partition. The reason for doing this
> > instead of, say, interleving individual messages is that it is a big
> > performance boost--making every message an entry in a blocking queue
> gives
> > a 5x performance hit in high-throughput cases. Perhaps this interleaving
> is
> > the problem?
> >
> > -Jay
> >
> >
> > On Sun, Aug 25, 2013 at 10:22 AM, Ian Friedman <[EMAIL PROTECTED] (mailto:
> [EMAIL PROTECTED])> wrote:
> >
> > > Sorry I reread what I've written so far and found that it doesn't state
> > > the actual problem very well. Let me clarify once again:
> > >
> > > The problem we're trying to solve is that we can't let messages go for
> > > unbounded amounts of time without getting processed, and it seems that
> > > something about what we're doing (which I suspect is the fact that
> > > consumers own several partitions but only consume from one of them at a
> > > time until it's caught up) is causing a small number of them to sit
> around
> > > for hours and hours. This is despite some consumers idling due to being
> > > fully caught up on the partitions they own. We've found that
> requeueing the
> > > oldest messages (consumers ignore messages that have already been
> > > processed) is fairly effective in getting them to go away, but I'm
> looking
> > > for a more stable solution.
> > >
> > > --
> > > Ian Friedman
> > >
> > >
> > > On Sunday, August 25, 2013 at 1:15 PM, Ian Friedman wrote:
> > >
> > > > When I said "some messages take longer than others" that may have
> been
> > > misleading. What I meant there is that the performance of the entire
> > > application is inconsistent, mostly due to pressure from other
> applications
> > > (mapreduce) on our HBase and MySQL backends. On top of that, some
> messages
> > > just contain more data. Now I suppose what you're suggesting is that I
> > > segment my messages by the average or expected time it takes the
> payloads
> > > to process, but I suspect what will happen if I do that is I will have
> > > several consumers doing nothing most of the time, and the rest of them
> > > backlogged inconsistently the same way they are now. The problem isn't
> so
> > > much the size of the payloads but the fact that we're seeing some
> messages,
> > > which i suspect are in partitions with lots of longer running
> processing
> > > tasks, sit around for hours without getting consumed. That's what I'm
> > > trying to solve.
> > > >
> > > > Is there any way to "add more consumers" without actually adding more
> > > consumer JVM processes? We've hit something of a saturation point for
> our
> > > MySQL database. Is this maybe where having multiple consumer threads
> would
> > > help? If so, given that I have a singular shared processing queue in
> each
> > > consumer, how would I leverage that to solve this problem?
> > > >
> > > > --
> > > > Ian Friedman

 
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Ian Friedman 2013-08-26, 18:19
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Jay Kreps 2013-08-26, 18:38
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Ian Friedman 2013-08-26, 21:43
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Ian Friedman 2013-08-26, 18:34