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 >
