Thanks for the advice, Guozhang.

Jagbir: I'll report back on my progress. I intend to have quite a few
threads across many machines. We'll see how well it performs with a whole
high-level consumer per thread.


On Thu, Jun 19, 2014 at 9:30 AM, Guozhang Wang <wangg...@gmail.com> wrote:

> Hello Kyle,
>
> For your first question, the first option would be preferable: it may use
> little bit more memory, and have more ZK writes. In 0.9 though, the offsets
> will be stored in Kafka servers instead of ZK, so you will no longer
> bombard ZK.
>
> For the third question, our designed usage pattern for manual commits would
> be:
>
> message = iter.next();
> process(message)
> consumer.commit();
>
> Thus if one crashes between process(message) and consumer.commit(), you do
> incur duplicates; but you will not get any data loss in this case. If you
> are more tolerable to data loss than duplicates, you can do:
>
> message = iter.next();
> consumer.commit();
> process(message)
>
>
> Guozhang
>
>
> On Wed, Jun 18, 2014 at 9:43 PM, Jagbir <jsho...@hotmail.com> wrote:
>
> > Hi Kyle,
> >
> > Thanks for the update.  Wondering if you found answer to your N-1 commit
> > question? If auto commit happens only at iterator.next () and onky for
> the
> > N -1 message then client code can be much simpler and reliable as you
> > mentioned. I'm also looking forward to any post in this regard.
> >
> > Jagbir
> >
> > On June 18, 2014 3:17:25 PM PDT, Kyle Banker <kyleban...@gmail.com>
> wrote:
> > >I think I've discovered the answer to my second question: according to
> > >the
> > >code in ZookeeperConsumerConnector.scala, a rebalance derives its
> > >offsets
> > >from what's already in Zookeeper. Therefore, uncommitted but consumed
> > >messages from a given partition will be replayed when the partition is
> > >reassigned.
> > >
> > >
> > >On Fri, Jun 13, 2014 at 3:01 PM, Kyle Banker <kyleban...@gmail.com>
> > >wrote:
> > >
> > >> I'm using Kafka 0.8.1.1.
> > >>
> > >> I have a simple goal: use the high-level consumer to consume a
> > >message
> > >> from Kafka, publish the message to a different system, and then
> > >commit the
> > >> message in Kafka. Based on my reading of the docs and the mailing
> > >list, it
> > >> seems like this isn't so easy to achieve. Here is my current
> > >understanding:
> > >>
> > >> First, I have to disable auto-commit. If the consumer automatically
> > >> commits, then I may lose messages if, for example, my process dies
> > >after
> > >> consuming but before publishing my message.
> > >>
> > >> Next, if my app is multi-threaded, I need to either
> > >>
> > >> a) use a separate consumer per thread (memory-intensive, hard on
> > >> Zookeeper) or
> > >> b) use a single consumer and assign a KafkaStream to each thread.
> > >Then,
> > >> when I want to commit, first synchronize all threads using a barrier.
> > >>
> > >> First question: is this correct so far?
> > >>
> > >>
> > >> Still, it appears that rebalancing may be a problem. In particular,
> > >this
> > >> sequence of events:
> > >>
> > >> 1. I'm consuming from a stream tied to two partitions, A and B.
> > >> 2. I consume a message, M, from partition A.
> > >> 3. Partition A gets assigned to a different consumer.
> > >> 4. I choose not to commit M or my process fails.
> > >>
> > >> Second question: When the partition is reassigned, will the message
> > >that I
> > >> consumed be automatically committed? If so, then there's no way to
> > >get the
> > >> reliability I want.
> > >>
> > >>
> > >> Third question: How do the folks at LinkedIn handle this overall use
> > >case?
> > >> What about other users?
> > >>
> > >> It seems to me that a lot of the complexity here could be easily
> > >addressed
> > >> by changing the way in which a partition's message pointer is
> > >advanced.
> > >> That is, when I consume message M, advance the pointer to message (M
> > >- 1)
> > >> rather than to M. In other words, calling iterator.next() would imply
> > >that
> > >> the previously consumed message may be safely committed. If this were
> > >the
> > >> case, I could simply enable auto-commit and be happy.
> > >>
> >
> > --
> > Sent from my Android phone with K-9 Mail. Please excuse my brevity.
>
>
>
>
> --
> -- Guozhang
>

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