-Re: High Level Consumer error handling and clean exit
Philip O'Toole 2013-07-09, 19:24
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.
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
> - set the next start offset for this topic/partition to this message in
> - 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.
> 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
> > considers it processed. So if your app subsequently crashes before the
> > message is fully processed, and "auto-commit" updates the offsets in
> > Zookeeper, you will drop that message.
> > The solution to this to call commitOffsets() explicitly.
> > Philip
> > On Tue, Jul 9, 2013 at 11:16 AM, Chris Curtin <[EMAIL PROTECTED]
> > >wrote:
> > > Hi,
> > >
> > > I'm working through a production-level High Level Consumer app and
> have a
> > > couple of error/shutdown questions to understand how the offset storage
> > is
> > > handled.
> > >
> > > Test case - simulate an error writing to destination application, for
> > > example a database, offset is 'lost'
> > >
> > > Scenario
> > > - write 500 messages for each topic/partition
> > > - use the example High Level Consumer code I wrote for the Wiki
> > > - Change the code so that every 10th read from the 'hasNext()'
> > > ConsumerIterator breaks out of the loop and returns from the thread,
> > > simulating a hard error. I write the offset to System.out to see what
> > > provided
> > > - startup again and look to see what offset was first emitted for a
> > > partition
> > >
> > > Issue: Kafka treats the offset for the message read that caused me to
> > break