Hey Chris, The way I handled this in my application using the High Level Consumer was to turn off auto-commit and commit manually after finishing a batch of messages (obviously you could do it after every message, but for my purposes it was better to have batches)
-- Ian Friedman On Tuesday, July 9, 2013 at 4:09 PM, Chris Curtin wrote: > Enhancement submitted: https://issues.apache.org/jira/browse/KAFKA-966 > > > > On Tue, Jul 9, 2013 at 3:53 PM, Chris Curtin <curtin.ch...@gmail.com > (mailto:curtin.ch...@gmail.com)> wrote: > > > 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 > > ZooKeeper? > > > > 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. > > > > Thanks, > > > > Chris > > > > > > > > On Tue, Jul 9, 2013 at 3:23 PM, Philip O'Toole <phi...@loggly.com > > (mailto:phi...@loggly.com)> 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 <curtin.ch...@gmail.com > > > (mailto:curtin.ch...@gmail.com)> > > > 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 <phi...@loggly.com > > > > (mailto:phi...@loggly.com)> > > > 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 > > > > > 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 <curtin.ch...@gmail.com > > > > > (mailto:curtin.ch...@gmail.com) > > > > > > 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 > > > > was > > > > > > 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 > > > > > > out of the loop as processed (as expected), but I really failed. How > > > > > > > > > > > > > > > > > > do I > > > > > > tell Kafka that I didn't really consume that offset? > > > > > > > > > > > > Here is the example code in the 'business logic': > > > > > > > > > > > > public void run() { > > > > > > ConsumerIterator<byte[], byte[]> it = m_stream.iterator(); > > > > > > int counter = 0; > > > > > > while (it.hasNext()) { > > > > > > MessageAndMetadata<byte[], byte[]> msg = it.next(); > > > > > > if (counter == 10) { > > > > > > System.out.println("Stopping Thread " + > > > > > > > > > > > > > > > > > > > > > > > > > m_threadNumber > > > > + > > > > > ": > > > > > > Partition: " + msg.partition() + > > > > > > ": Offset: " + msg.offset() + " :" + new > > > > > > String(msg.message())); > > > > > > break; > > > > > > } > > > > > > System.out.println("Thread " + m_threadNumber + ": > > > > > > > > > > > > > > > > Partition: " > > > > > > + msg.partition() + > > > > > > ": Offset: " + msg.offset() + " :" + new > > > > > > String(msg.message())); > > > > > > counter++; > > > > > > } > > > > > > > > > > > > System.out.println("Shutting down Thread: " + > > > m_threadNumber); > > > > > > } > > > > > > > > > > > > I understand that handling 'hard' errors like JVM crashes, kill -9 > > > etc. > > > > > may > > > > > > leave the offsets in ZooKeeper incorrect, but I'm trying to > > > > > > > > > > > > > > > > > > > > understand > > > > > what > > > > > > happens in a clean shutdown where Kafka and the Consumer are > > > > > > > > > > > > > > > > > > > > behaving > > > > > > correctly but I can't process what I read. > > > > > > > > > > > > This also feels like I'm blurring SimpleConsumer theory into this, > > > but > > > > > > except for the exception/shutdown case High Level Consumer does > > > > > > > > > > everything > > > > > > I want. > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > Chris
