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From Kamal Chandraprakash <kamal.chandraprak...@gmail.com>
Subject Re: [VOTE] KIP-520: Augment Consumer.committed(partition) to allow multiple partitions
Date Wed, 11 Sep 2019 07:16:51 GMT
Thanks for the KIP!

LGTM, +1 (non-binding).

On Wed, Sep 11, 2019 at 3:23 AM Matthias J. Sax <matthias@confluent.io>
wrote:

> I don't have a strong preference. So I am also fine to deprecate the
> existing methods. Let's see what Jason thinks.
>
> Can you update the KIP to reflect the semantics of the return `Map` (ie,
> does only contain entries for partitions with committed offsets, and
> does not contain `null` values)?
>
>
> +1 (binding)
>
> -Matthias
>
>
>
>
> On 9/10/19 11:53 AM, Guozhang Wang wrote:
> > Hi Jason / Matthias,
> >
> > I understand your concerns now. Just to clarify my main motivation on
> > deprecating the old APIs is not only for aesthetics (confess I personally
> > do have preference on succinct APIs), but to urge people to use the
> batched
> > API for better latency when possible --- as stated in the KIP, my
> > observation is that in practice most callers are actually going to get
> > committed offsets for more than one partitions, and without deprecating
> the
> > old APIs it would be hard for them to realize that the new API does have
> a
> > benefit in performance.
> >
> > This is different from some of the existing APIs though -- e.g., Matthias
> > mentioned about seek / seekToBeginning / seekToEnd, where only seekToXX
> > have plurals and seek only have singulars. We can, of course, make
> seekToXX
> > with plurals as well just like commitSync/Async, but since seeks are
> > non-blocking APIs (they rely on the follow-up polling call to talk to the
> > brokers) either calling it multiple times with one partition each v.s.
> > calling it one time with a plural makes little difference (still, I'd
> argue
> > that today we do not have a same-named function overloaded with both
> types
> > :P) On the other hand, committed, commitSync, offsetsForTimes etc
> blocking
> > calls are all in the form of plurals except
> >
> > * committed
> > * position
> > * partitionsFor
> >
> > My rationale was that 1) for consecutive calls of #position, mostly it
> > would only require a single round-trip to brokers since we are trying to
> > refresh fetching positions for all partitions anyways, and 2) for
> > #partitionsFor, theoretically we could also consider to ask for multiple
> > topics in one call since each blocking call potentially incurs one round
> > trip, but I did not include it in the scope of this KIP only because I
> have
> > not observed too many usage patterns that are commonly calling it
> > consecutively for multiple topics. At the moment, what I truly want to
> > "improve" on is the committed calls, as in many cases I've seen it being
> > called consecutively for multiple topic-partitions.
> >
> > Therefore, I'm still more inclined to deprecate the old APIs so that we
> can
> > enforce people to discover the new batching APIs for efficiency in this
> > KIP. But if you feel that this compatibility is very crucial to maintain
> I
> > could be convinced.
> >
> >
> > Guozhang
> >
> > On Tue, Sep 10, 2019 at 10:18 AM Matthias J. Sax <matthias@confluent.io>
> > wrote:
> >
> >> Thanks for the KIP Guozhang.
> >>
> >>> Another reason is that other functions of KafkaConsumers do not have
> >> those
> >>> overloaded functions to be consistent
> >>
> >> I tend to agree with Jason about keeping the existing methods. Your
> >> argument does not seem to hold. I just checked the `Consumer` API, and
> >> it's mix of overloads:
> >>
> >> Methods only talking `Collections`
> >>
> >>
> >>
> subscribe/assign/commitSync/commitAsyn/pause/resume/offsetsForTimes/beginningOffsets/endOffsets
> >>
> >> Method with overload taking `Collections` or as single value:
> >>
> >> seek/seekToBeginning/seekToEnd
> >>
> >> (those are strictly different methods, but they are semantically
> related)
> >>
> >> Only talking single value:
> >>
> >> position/committed/partitionsFor
> >>
> >>
> >> While you are strictly speaking correct, that there is no method with an
> >> overload for `Collection` and single value, the API mix seems to suggest
> >> that it might actually be worth to have corresponding overloads for all
> >> methods instead of sticking to `Collections` only.
> >>
> >>
> >>
> >> About the return map: I agree that not containing any entry in the map
> >> is better. It's not only consistent with other APIs but it also avoids
> >> potential NPEs.
> >>
> >>
> >>
> >> -Matthias
> >>
> >>
> >> On 9/10/19 10:04 AM, Jason Gustafson wrote:
> >>>>  I feel it not worth making committed to have both plurals and
> >> singulars.
> >>>
> >>> Not sure I agree. If we had started with these new APIs from the
> >> beginning,
> >>> that may have been better, but we already have exposed the singular
> APIs
> >>> and users are depending on them. Not sure it's worth breaking
> >> compatibility
> >>> just for aesthetics.
> >>>
> >>> -Jason
> >>>
> >>> On Tue, Sep 10, 2019 at 9:41 AM Guozhang Wang <wangguoz@gmail.com>
> >> wrote:
> >>>
> >>>> Thanks Jason!
> >>>>
> >>>> On Tue, Sep 10, 2019 at 9:07 AM Jason Gustafson <jason@confluent.io>
> >>>> wrote:
> >>>>
> >>>>> Hi Guozhang,
> >>>>>
> >>>>> I think the motivation for the new API makes sense. I've wanted
> >> something
> >>>>> like this in the past. That said, do you think there is a substantial
> >>>>> benefit from deprecating the old API? I can still see it being
> >> convenient
> >>>>> in some cases and it's no real cost to maintain.
> >>>>>
> >>>>>
> >>>> That's a good question.
> >>>>
> >>>> Personally I would like to keep a succinct set of APIs out of the box
> >> and
> >>>> let users who want more syntax sugars to add themselves as extended
> >> classes
> >>>> for example (KafkaConsumer is not a final class).
> >>>> Another reason is that other functions of KafkaConsumers do not have
> >> those
> >>>> overloaded functions to be consistent, e.g. we do not have a
> >>>> subscribe(single-topic), pause/resume(single-topic-partition) or
> >>>> seekToBeginning(single-topic-partition). I feel it not worth making
> >>>> committed to have both plurals and singulars.
> >>>>
> >>>> WDYT?
> >>>>
> >>>>
> >>>>> Also, just a minor detail. If the partition has no committed offset,
> >> will
> >>>>> it be present in the map with a null value?
> >>>>>
> >>>>> I looked into the admin client's listConsumerGroupOffsets call when
> >>>> creating the KIP, and to be consistent with that API my intention is
> to
> >> NOT
> >>>> include the entry if a topic-partition does not have committed
> offsets.
> >>>> That said, if we feel returning an entry with null value is better for
> >>>> programmability I can also do that (and will update wiki page to
> >> clarify as
> >>>> well). LMK.
> >>>>
> >>>>
> >>>>> -Jason
> >>>>>
> >>>>> On Tue, Sep 10, 2019 at 6:09 AM Mickael Maison <
> >> mickael.maison@gmail.com
> >>>>>
> >>>>> wrote:
> >>>>>
> >>>>>> +1 (non-binding), thanks Guozhang
> >>>>>>
> >>>>>> On Tue, Sep 10, 2019 at 1:14 AM Boyang Chen <
> >>>> reluctanthero104@gmail.com>
> >>>>>> wrote:
> >>>>>>>
> >>>>>>> Hey Guozhang,
> >>>>>>>
> >>>>>>> LGTM, +1 (non-binding)
> >>>>>>>
> >>>>>>> On Mon, Sep 9, 2019 at 5:07 PM Guozhang Wang <wangguoz@gmail.com>
> >>>>> wrote:
> >>>>>>>
> >>>>>>>> Hello folks,
> >>>>>>>>
> >>>>>>>> I've created a new KIP allowing consumer.committed to
take a set
> of
> >>>>>>>> partitions instead of just one partition to allow batching
effects
> >>>> of
> >>>>>> such
> >>>>>>>> requests (the protocol already allows us to send multiple
> >>>> partitions
> >>>>>> in one
> >>>>>>>> round-trip):
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>
> >>>>>
> >>>>
> >>
> https://cwiki.apache.org/confluence/display/KAFKA/KIP-520%3A+Add+overloaded+Consumer%23committed+for+batching+partitions
> >>>>>>>>
> >>>>>>>> Since it is a pretty straight-forward KIP, I'm starting
the VOTE
> >>>> for
> >>>>>> this
> >>>>>>>> KIP directly. If there are any suggestions about this
proposal,
> >>>>> please
> >>>>>> feel
> >>>>>>>> free to share them in this thread. Thank you!
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> -- Guozhang
> >>>>>>>>
> >>>>>>
> >>>>>
> >>>>
> >>>>
> >>>> --
> >>>> -- Guozhang
> >>>>
> >>>
> >>
> >>
> >
>
>

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