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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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Re: Consumer throughput imbalance
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.  

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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
> > >
> > >
> > > On Sunday, August 25, 2013 at 12:13 PM, Mark wrote:
> > >
> > > > I don't think it would matter as long as you separate the types of
> > message in different topics. Then just add more consumers to the ones that
> > are slow. Am I missing something?
> > > >
> > > > On Aug 25, 2013, at 8:59 AM, Ian Friedman <[EMAIL PROTECTED] (mailto:[EMAIL PROTECTED]) (mailto:
> > [EMAIL PROTECTED] (mailto:[EMAIL PROTECTED]))> wrote:

 
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Jay Kreps 2013-08-26, 17:27
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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