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Kafka >> mail # user >> High Level Consumer error handling and clean exit

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Re: High Level Consumer error handling and clean exit
Thanks. I know I can write a SimpleConsumer to do this, but it feels like
the High Level consumer is _so_ close to being robust enough to    handle
what I'd think people want to do in most applications. I'm going to submit
an enhancement request.

I'm trying to understand the level of data loss in this situation, so I
looked deeper into the KafkaStream logic: it looks like a KafkaStream
includes a BlockingQueue for transferring the messages to my code from
Kafka. If I call shutdown() when I detect the problem, are the messages
already in the BlockingQueue considered 'read' by Kafka, or does the
shutdown peek into the Queue to see what is still there before updating

My concern is if that queue is not empty I'll be losing more than the one
message that led to the failure.

I'm also curious how others are handling this situation. Do you assume the
message that is causing problems is lost or somehow know to go get it
later? I'd think others would have this problem too.



On Tue, Jul 9, 2013 at 3:23 PM, Philip O'Toole <[EMAIL PROTECTED]> wrote:

> OK.
> It sounds like you're requesting functionality that the high-level consumer
> simply doesn't have. As I am sure you know, there is no API call that
> supports "handing back a message".
> I might be missing something, but if you need this kind of control, I think
> you need to code your application differently. You could try creating a
> ConsumerConnection per partition (your clients will then need to know the
> number of partitions out there). That way commitOffsets() will actually
> only apply to that partition. Auto-commit the same way. It might give you
> the level of control you need.
> Philip
> On Tue, Jul 9, 2013 at 2:22 PM, Chris Curtin <[EMAIL PROTECTED]>
> wrote:
> > Hi Philip,
> >
> > Correct, I don't want to explicitly control the offset committing. The
> > ConsumerConnector handles that well enough except for when I want to
> > shutdown and NOT have Kafka think I consumed that last message for a
> > stream. This isn't the crash case, it is a case where the logic consuming
> > the message detects and error and wants to cleanly exit until that issue
> > can be resolved, but not lose the message it was trying to process when
> the
> > problem is resolved.
> >
> > My understanding is that the commitOffsets() call is across all threads,
> > not just for the stream my thread is reading from. So knowing it is okay
> to
> > call this requires coordination across all my threads, which makes a High
> > Level Consumer a lot harder to write correctly.
> >
> > Thinking about what I'd like to happen is: my code hands the message back
> > to the KafkaStream (or whatever level knows about the consumed offsets)
> and
> > says
> > - set the next start offset for this topic/partition to this message in
> > ZooKeeper
> > - cleanly shutdown the stream from the broker(s)
> > - don't force a rebalance on the consumer since something is wrong with
> > processing of the data in the message, not the message.
> > - If I try to use the stream again I should get an exception
> > - I don't think I would want this to cause a complete shutdown of the
> > ConsumerConnector, in case other threads are still processing. If all
> > threads have the same issue they will all fail soon enough and do the
> same
> > logic. But if only one thread fails, our Operations teams will need to
> > resolve the issue then do a clean restart to recover.
> >
> > I think this logic would only happen when the down stream system was
> having
> > issues since the iterator would be drained correctly when the 'shutdown'
> > call to ConsumerConnector is made.
> >
> > Thanks,
> >
> > Chris
> >
> >
> >
> > On Tue, Jul 9, 2013 at 11:21 AM, Philip O'Toole <[EMAIL PROTECTED]>
> wrote:
> >
> > > It seems like you're not explicitly controlling the offsets. Is that
> > > correct?
> > >
> > > If so, the moment you pull a message from the stream, the client
> > framework
> > > considers it processed. So if your app subsequently crashes before the