Robert,
For the push orient api, you can potentially implement your own
MessageHandler with those methods. In the main loop of our new consumer
api, you can just call those methods based on the events you get.
Also, we already have an api to get the first and the last offset of a
partition (getOffsetBefore).
Thanks,
Jun
On Sat, Feb 22, 2014 at 11:29 AM, Withers, Robert
<robert.with...@dish.com>wrote:
> This is a good idea, too. I would modify it to include stream marking,
> then you can have:
>
> long end = consumer.lastOffset(tp);
> consumer.setMark(end);
> while(consumer.beforeMark()) {
> process(consumer.pollToMark());
> }
>
> or
>
> long end = consumer.lastOffset(tp);
> consumer.setMark(end);
> for(Object msg : consumer.iteratorToMark()) {
> process(msg);
> }
>
> I actually have 4 suggestions, then:
>
> * pull: stream marking
> * pull: finite streams, bound by time range (up-to-now, yesterday) or
> offset
> * pull: async api
> * push: KafkaMessageSource, for a push model, with msg and OOB events.
> Build one in either individual or chunk mode and have a listener for each
> msg or a listener for a chunk of msgs. Make it composable and policy
> driven (chunked, range, commitOffsets policy, retry policy, transactional)
>
> Thank you,
> Robert
>
> On Feb 22, 2014, at 11:21 AM, Jay Kreps <jay.kr...@gmail.com<mailto:
> jay.kr...@gmail.com>> wrote:
>
> I think what Robert is saying is that we need to think through the offset
> API to enable "batch processing" of topic data. Think of a process that
> periodically kicks off to compute a data summary or do a data load or
> something like that. I think what we need to support this is an api to
> fetch the last offset from the server for a partition. Something like
> long lastOffset(TopicPartition tp)
> and for symmetry
> long firstOffset(TopicPartition tp)
>
> Likely this would have to be batched. Essentially we should add this use
> case to our set of code examples to write and think through.
>
> The usage would be something like
>
> long end = consumer.lastOffset(tp);
> while(consumer.position < end)
> process(consumer.poll());
>
> -Jay
>
>
> On Sat, Feb 22, 2014 at 1:52 AM, Withers, Robert <robert.with...@dish.com
> <mailto:robert.with...@dish.com>>wrote:
>
> Jun,
>
> I was originally thinking a non-blocking read from a distributed stream
> should distinguish between "no local messages, but a fetch is occurring"
> versus "you have drained the stream". The reason this may be valuable to
> me is so I can write consumers that read all known traffic then terminate.
> You caused me to reconsider and I think I am conflating 2 things. One is
> a sync/async api while the other is whether to have an infinite or finite
> stream. Is it possible to build a finite KafkaStream on a range of
> messages?
>
> Perhaps a Simple Consumer would do just fine and then I could start off
> getting the writeOffset from zookeeper and tell it to read a specified
> range per partition. I've done this and forked a simple consumer runnable
> for each partition, for one of our analyzers. The great thing about the
> high-level consumer is that rebalance, so I can fork however many stream
> readers I want and you just figure it out for me. In that way you offer us
> the control over the resource consumption within a pull model. This is
> best to regulate message pressure, they say.
>
> Combining that high-level rebalance ability with a ranged partition drain
> could be really nice...build the stream with an ending position and it is a
> finite stream, but retain the high-level rebalance. With a finite stream,
> you would know the difference of the 2 async scenarios: fetch-in-progress
> versus end-of-stream. With an infinite stream, you never get
> end-of-stream.
>
> Aside from a high-level consumer over a finite range within each
> partition, the other feature I can think of is more complicated. A
> high-level consumer has state machine changes that the client cannot
> access, to my knowledge. Our use of kafka has us invoke a message handler
> with each message we consumer from the KafkaStream, so we convert a
> pull-model to a push-model. Including the idea of receiving notifications
> from state machine changes, what would be really nice is to have a
> KafkaMessageSource, that is an eventful push model. If it were
> thread-safe, then we could register listeners for various events:
>
> * opening-stream
> * closing-stream
> * message-arrived
> * end-of-stream/no-more-messages-in-partition (for finite streams)
> * rebalance started
> * partition assigned
> * partition unassigned
> * rebalance finished
> * partition-offset-committed
>
> Perhaps that is just our use, but instead of a pull-oriented KafkaStream,
> is there any sense in your providing a push-oriented KafkaMessageSource
> publishing OOB messages?
>
> thank you,
> Robert
>
> On Feb 21, 2014, at 5:59 PM, Jun Rao <jun...@gmail.com<mailto:
> jun...@gmail.com><mailto:
> jun...@gmail.com<mailto:jun...@gmail.com>>> wrote:
>
> Robert,
>
> Could you explain why you want to distinguish btw
> FetchingInProgressException
> and NoMessagePendingException? The nextMsgs() method that you want is
> exactly what poll() does.
>
> Thanks,
>
> Jun
>
>
> On Wed, Feb 19, 2014 at 8:45 AM, Withers, Robert <robert.with...@dish.com
> <mailto:robert.with...@dish.com>
> <mailto:robert.with...@dish.com>>wrote:
>
> I am not clear on why the consumer stream should be positionable,
> especially if it is limited to the in-memory fetched messages. Could
> someone explain to me, please? I really like the idea of committing the
> offset specifically on those partitions with changed read offsets, only.
>
>
>
> 2 items I would like to see added to the KafkaStream are:
>
> * a non-blocking next(), throws several exceptions
> (FetchingInProgressException and a NoMessagePendingException or something)
> to differentiate between fetching or no messages left.
>
> * A nextMsgs() method which returns all locally available messages
> and kicks off a fetch for the next chunk.
>
>
>
> If you are trying to add transactional features, then formally define a
> DTP capability and pull in other server frameworks to share the
> implementation. Should it be XA/Open? How about a new peer2peer DTP
> protocol?
>
>
>
> Thank you,
>
> Robert
>
>
>
> Robert Withers
>
> Staff Analyst/Developer
>
> o: (720) 514-8963
>
> c: (571) 262-1873
>
>
>
> -----Original Message-----
> From: Jay Kreps [mailto:jay.kr...@gmail.com]
> Sent: Sunday, February 16, 2014 10:13 AM
> To: users@kafka.apache.org<mailto:users@kafka.apache.org><mailto:
> users@kafka.apache.org>
> Subject: Re: New Consumer API discussion
>
>
>
> +1 I think those are good. It is a little weird that changing the fetch
>
> point is not batched but changing the commit point is, but I suppose there
> is no helping that.
>
>
>
> -Jay
>
>
>
>
>
> On Sat, Feb 15, 2014 at 7:52 AM, Neha Narkhede <neha.narkh...@gmail.com
> <mailto:neha.narkh...@gmail.com>
> <mailto:neha.narkh...@gmail.com>
> <mailto:neha.narkh...@gmail.com>>wrote:
>
>
>
> Jay,
>
>
>
> That makes sense. position/seek deal with changing the consumers
>
> in-memory data, so there is no remote rpc there. For some reason, I
>
> got committed and seek mixed up in my head at that time :)
>
>
>
> So we still end up with
>
>
>
> long position(TopicPartition tp)
>
> void seek(TopicPartitionOffset p)
>
> Map<TopicPartition, Long> committed(TopicPartition tp);
>
> void commit(TopicPartitionOffset...);
>
>
>
> Thanks,
>
> Neha
>
>
>
> On Friday, February 14, 2014, Jay Kreps <jay.kr...@gmail.com<mailto:
> jay.kr...@gmail.com><mailto:
> jay.kr...@gmail.com<mailto:jay.kr...@gmail.com>><mailto:
> jay.kr...@gmail.com<mailto:jay.kr...@gmail.com><mailto:jay.kr...@gmail.com>>>
> wrote:
>
>
>
> Oh, interesting. So I am assuming the following implementation:
>
> 1. We have an in-memory fetch position which controls the next fetch
>
> offset.
>
> 2. Changing this has no effect until you poll again at which point
>
> your fetch request will be from the newly specified offset 3. We
>
> then have an in-memory but also remotely stored committed offset.
>
> 4. Calling commit has the effect of saving the fetch position as
>
> both the in memory committed position and in the remote store 5.
>
> Auto-commit is the same as periodically calling commit on all
>
> positions.
>
>
>
> So batching on commit as well as getting the committed position
>
> makes sense, but batching the fetch position wouldn't, right? I
>
> think you are actually thinking of a different approach.
>
>
>
> -Jay
>
>
>
>
>
> On Thu, Feb 13, 2014 at 10:40 PM, Neha Narkhede
>
> <neha.narkh...@gmail.com<mailto:neha.narkh...@gmail.com><mailto:
> neha.narkh...@gmail.com>
>
> <javascript:;>
>
> wrote:
>
>
>
> I think you are saying both, i.e. if you have committed on a
>
> partition it returns you that value but if you
>
> haven't
>
> it does a remote lookup?
>
>
>
> Correct.
>
>
>
> The other argument for making committed batched is that commit()
>
> is batched, so there is symmetry.
>
>
>
> position() and seek() are always in memory changes (I assume) so
>
> there
>
> is
>
> no need to batch them.
>
>
>
> I'm not as sure as you are about that assumption being true.
>
> Basically
>
> in
>
> my example above, the batching argument for committed() also
>
> applies to
>
> position() since one purpose of fetching a partition's offset is
>
> to use
>
> it
>
> to set the position of the consumer to that offset. Since that
>
> might
>
> lead
>
> to a remote OffsetRequest call, I think we probably would be
>
> better off batching it.
>
>
>
> Another option for naming would be position/reposition instead of
>
> position/seek.
>
>
>
> I think position/seek is better since it aligns with Java file APIs.
>
>
>
> I also think your suggestion about ConsumerPosition makes sense.
>
>
>
> Thanks,
>
> Neha
>
> On Feb 13, 2014 9:22 PM, "Jay Kreps" <jay.kr...@gmail.com<mailto:
> jay.kr...@gmail.com><mailto:
> jay.kr...@gmail.com<mailto:jay.kr...@gmail.com>><mailto:
> jay.kr...@gmail.com<mailto:jay.kr...@gmail.com><mailto:jay.kr...@gmail.com>>>
> wrote:
>
>
>
> Hey Neha,
>
>
>
> I actually wasn't proposing the name TopicOffsetPosition, that
>
> was
>
> just a
>
> typo. I meant TopicPartitionOffset, and I was just referencing
>
> what
>
> was
>
> in
>
> the javadoc. So to restate my proposal without the typo, using
>
> just
>
> the
>
> existing classes (that naming is a separate question):
>
> long position(TopicPartition tp)
>
> void seek(TopicPartitionOffset p)
>
> long committed(TopicPartition tp)
>
> void commit(TopicPartitionOffset...);
>
>
>
> So I may be unclear on committed() (AKA lastCommittedOffset). Is
>
> it returning the in-memory value from the last commit by this
>
> consumer,
>
> or
>
> is
>
> it doing a remote fetch, or both? I think you are saying both, i.e.
>
> if
>
> you
>
> have committed on a partition it returns you that value but if
>
> you
>
> haven't
>
> it does a remote lookup?
>
>
>
> The other argument for making committed batched is that commit()
>
> is batched, so there is symmetry.
>
>
>
> position() and seek() are always in memory changes (I assume) so
>
> there
>
> is
>
> no need to batch them.
>
>
>
> So taking all that into account what if we revise it to
>
> long position(TopicPartition tp)
>
> void seek(TopicPartitionOffset p)
>
> Map<TopicPartition, Long> committed(TopicPartition tp);
>
> void commit(TopicPartitionOffset...);
>
>
>
> This is not symmetric between position/seek and commit/committed
>
> but
>
> it
>
> is
>
> convenient. Another option for naming would be
>
> position/reposition
>
> instead
>
> of position/seek.
>
>
>
> With respect to the name TopicPartitionOffset, what I was trying
>
> to
>
> say
>
> is
>
> that I recommend we change that to something shorter. I think
>
> TopicPosition
>
> or ConsumerPosition might be better. Position does not refer to
>
> the variables in the object, it refers to the meaning of the
>
> object--it represents a position within a topic. The offset
>
> field in that object
>
> is
>
> still called the offset. TopicOffset, PartitionOffset, or
>
> ConsumerOffset
>
> would all be workable too. Basically I am just objecting to
>
> concatenating
>
> three nouns together. :-)
>
>
>
> -Jay
>
>
>
>
>
>
>
>
>
>
>
> On Thu, Feb 13, 2014 at 1:54 PM, Neha Narkhede <
>
> neha.narkh...@gmail.com<mailto:neha.narkh...@gmail.com><mailto:
> neha.narkh...@gmail.com><mailto:
> neha.narkh...@gmail.com<mailto:neha.narkh...@gmail.com>>
>
> wrote:
>
>
>
> 2. It returns a list of results. But how can you use the list?
>
> The
>
> only
>
> way
>
> to use the list is to make a map of tp=>offset and then look
>
> up
>
> results
>
> in
>
> this map (or do a for loop over the list for the partition you
>
> want). I
>
> recommend that if this is an in-memory check we just do one at
>
> a
>
> time.
>
> E.g.
>
> long committedPosition(
>
> TopicPosition).
>
>
>
> This was discussed in the previous emails. There is a choic
>
>
>
>
> --
> Robert Withers
> robert.with...@dish.com<mailto:robert.with...@dish.com><mailto:
> robert.with...@dish.com>
> c: 303.919.5856
>
>
>
> --
> Robert Withers
> robert.with...@dish.com<mailto:robert.with...@dish.com>
> c: 303.919.5856
>
>
