Hi Jark,
Please see the reply below:
Regarding to option#3, my concern is that if we don't support streaming
> mode for bounded source,
> how could we create a testing source for streaming mode? Currently, all the
> testing source for streaming
> are bounded, so that the integration test will finish finally.
An UNBOUNDED source does not mean it will never stops. It simply indicates
that the source *may* run forever, so the runtime needs to be prepared for
that, but the task may still stop at some point when it hits some
source-specific condition. So an UNBOUNDED testing source can still stop at
some point if needed.
Regarding to Source#getRecordOrder(), could we have a implicit contract
> that unbounded source should
> already read in order (i.e. reading partitions in parallel), for bounded
> source the order is not mandatory.
> This is also the behaviors of the current sources.
1) a source can't guarantee it reads in strict order, because the producer
> may produce data not in order.
> 2) *Bounded-StrictOrder* is not necessary, because batch can reorder data.
It is true that sometimes the source cannot guarantee the record order, but
sometimes it can. Right now, even for stream processing, there is no
processing order guarantee. For example, a join operator may emit a later
record which successfully found a join match earlier.
Event order is one of the most important requirements for event processing,
a clear order guarantee would be necessary. That said, I agree that right
now even if the sources provide the record order requirement, the runtime
is not able to guarantee that out of the box. So I am OK if we add the
record order to the Source later. But we should avoid misleading users to
make them think the processing order is guaranteed when using the unbounded
runtime.
Thanks,
Jiangjie (Becket) Qin
On Wed, Dec 18, 2019 at 10:29 AM Jark Wu <imj...@gmail.com> wrote:
> Hi Becket,
>
> That's great we have reached a consensus on Source#getBoundedness().
>
> Regarding to option#3, my concern is that if we don't support streaming
> mode for bounded source,
> how could we create a testing source for streaming mode? Currently, all the
> testing source for streaming
> are bounded, so that the integration test will finish finally.
>
> Regarding to Source#getRecordOrder(), could we have a implicit contract
> that unbounded source should
> already read in order (i.e. reading partitions in parallel), for bounded
> source the order is not mandatory.
> This is also the behaviors of the current sources.
> 1) a source can't guarantee it reads in strict order, because the producer
> may produce data not in order.
> 2) *Bounded-StrictOrder* is not necessary, because batch can reorder data.
>
> Best,
> Jark
>
>
>
> On Tue, 17 Dec 2019 at 22:03, Becket Qin <becket....@gmail.com> wrote:
>
> > Hi folks,
> >
> > Thanks for the comments. I am convinced that the Source API should not
> take
> > boundedness as a parameter after it is constructed. What Timo and Dawid
> > suggested sounds a reasonable solution to me. So the Source API would
> > become:
> >
> > Source {
> > Boundedness getBoundedness();
> > }
> >
> > Assuming the above Source API, in addition to the two options mentioned
> in
> > earlier emails, I am thinking of another option:
> >
> > *Option 3:*
> > // MySource must be unbounded, otherwise throws exception.
> > DataStream<Type> dataStream = env.source(mySource);
> >
> > // MySource must be bounded, otherwise throws exception.
> > BoundedDataStream<Type> boundedDataStream = env.boundedSource(mySource);
> >
> > The pros of this API are:
> > a) It fits the requirements from Table / SQL well.
> > b) DataStream users still have type safety (option 2 only has partial
> > type safety).
> > c) Cristal clear boundedness from the API which makes DataStream join
> /
> > connect easy to reason about.
> > The caveats I see,
> > a) It is inconsistent with Table since Table has one unified
> interface.
> > b) No streaming mode for bounded source.
> >
> > @Stephan Ewen <ewenstep...@gmail.com> @Aljoscha Krettek
> > <aljos...@ververica.com> what do you think of the approach?
> >
> >
> > Orthogonal to the above API, I am wondering whether boundedness is the
> only
> > dimension needed to describe the characteristic of the Source behavior.
> We
> > may also need to have another dimension of *record order*.
> >
> > For example, when a file source is reading from a directory with bounded
> > records, it may have two ways to read.
> > 1. Read files in parallel.
> > 2. Read files in the chronological order.
> > In both cases, the file source is a Bounded Source. However, the
> processing
> > requirement for downstream may be different. In the first case, the
> > record processing and result emitting order does not matter, e.g. word
> > count. In the second case, the records may have to be processed in the
> > order they were read, e.g. change log processing.
> >
> > If the Source only has a getBoundedness() method, the downstream
> processors
> > would not know whether the records emitted from the Source should be
> > processed in order or not. So combining the boundedness and record order,
> > we will have four scenarios:
> >
> > *Bounded-StrictOrder*: A segment of change log.
> > *Bounded-Random*: Batch Word Count.
> > *Unbounded-StrictOrder*: An infinite change log.
> > *Unbounded-Random*: Streaming Word Count.
> >
> > Option 2 mentioned in the previous email was kind of trying to handle the
> > Bounded-StrictOrder case by creating a DataStream from a bounded source,
> > which actually does not work.
> > It looks that we do not have strict order support in some operators at
> this
> > point, e.g. join. But we may still want to add the semantic to the Source
> > first so later on we don't need to change all the source implementations,
> > especially given that many of them will be implemented by 3rd party.
> >
> > Given that, we need another dimension of *Record Order* in the Source.
> More
> > specifically, the API would become:
> >
> > Source {
> > Boundedness getBoundedness();
> > RecordOrder getRecordOrder();
> > }
> >
> > public enum RecordOrder {
> > /** The record in the DataStream must be processed in its strict
> order
> > for correctness. */
> > STRICT,
> > /** The record in the DataStream can be processed in arbitrary order.
> > */
> > RANDOM;
> > }
> >
> > Any thoughts?
> >
> > Thanks,
> >
> > Jiangjie (Becket) Qin
> >
> > On Tue, Dec 17, 2019 at 3:44 PM Timo Walther <twal...@apache.org> wrote:
> >
> > > Hi Becket,
> > >
> > > I completely agree with Dawid's suggestion. The information about the
> > > boundedness should come out of the source. Because most of the
> streaming
> > > sources can be made bounded based on some connector specific criterion.
> > > In Kafka, it would be an end offset or end timestamp but in any case
> > > having just a env.boundedSource() is not enough because parameters for
> > > making the source bounded are missing.
> > >
> > > I suggest to have a simple `isBounded(): Boolean` flag in every source
> > > that might be influenced by a connector builder as Dawid mentioned.
> > >
> > > For type safety during programming, we can still go with *Final state
> > > 1*. By having a env.source() vs env.boundedSource(). The latter would
> > > just enforce that the boolean flag is set to `true` and could make
> > > bounded operations available (if we need that actually).
> > >
> > > However, I don't think that we should start making a unified Table API
> > > ununified again. Boundedness is an optimization property. Every bounded
> > > operation can also executed in an unbounded way using
> updates/retraction
> > > or watermarks.
> > >
> > > Regards,
> > > Timo
> > >
> > >
> > > On 15.12.19 14:22, Becket Qin wrote:
> > > > Hi Dawid and Jark,
> > > >
> > > > I think the discussion ultimately boils down to the question that
> which
> > > one
> > > > of the following two final states do we want? Once we make this
> > decision,
> > > > everything else can be naturally derived.
> > > >
> > > > *Final state 1*: Separate API for bounded / unbounded DataStream &
> > Table.
> > > > That means any code users write will be valid at the point when they
> > > write
> > > > the code. This is similar to having type safety check at programming
> > > time.
> > > > For example,
> > > >
> > > > BoundedDataStream extends DataStream {
> > > > // Operations only available for bounded data.
> > > > BoundedDataStream sort(...);
> > > >
> > > > // Interaction with another BoundedStream returns a Bounded stream.
> > > > BoundedJoinedDataStream join(BoundedDataStream other)
> > > >
> > > > // Interaction with another unbounded stream returns an unbounded
> > stream.
> > > > JoinedDataStream join(DataStream other)
> > > > }
> > > >
> > > > BoundedTable extends Table {
> > > > // Bounded only operation.
> > > > BoundedTable sort(...);
> > > >
> > > > // Interaction with another BoundedTable returns a BoundedTable.
> > > > BoundedTable join(BoundedTable other)
> > > >
> > > > // Interaction with another unbounded table returns an unbounded
> table.
> > > > Table join(Table other)
> > > > }
> > > >
> > > > *Final state 2*: One unified API for bounded / unbounded DataStream /
> > > > Table.
> > > > That unified API may throw exception at DAG compilation time if an
> > > invalid
> > > > operation is tried. This is what Table API currently follows.
> > > >
> > > > DataStream {
> > > > // Throws exception if the DataStream is unbounded.
> > > > DataStream sort();
> > > > // Get boundedness.
> > > > Boundedness getBoundedness();
> > > > }
> > > >
> > > > Table {
> > > > // Throws exception if the table has infinite rows.
> > > > Table orderBy();
> > > >
> > > > // Get boundedness.
> > > > Boundedness getBoundedness();
> > > > }
> > > >
> > > >>From what I understand, there is no consensus so far on this decision
> > > yet.
> > > > Whichever final state we choose, we need to make it consistent across
> > the
> > > > entire project. We should avoid the case that Table follows one final
> > > state
> > > > while DataStream follows another. Some arguments I am aware of from
> > both
> > > > sides so far are following:
> > > >
> > > > Arguments for final state 1:
> > > > 1a) Clean API with method safety check at programming time.
> > > > 1b) (Counter 2b) Although SQL does not have programming time error
> > > check, SQL
> > > > is not really a "programming language" per se. So SQL can be
> different
> > > from
> > > > Table and DataStream.
> > > > 1c) Although final state 2 seems making it easier for SQL to use
> given
> > > it
> > > > is more "config based" than "parameter based", final state 1 can
> > probably
> > > > also meet what SQL wants by wrapping the Source in TableSource /
> > > > TableSourceFactory API if needed.
> > > >
> > > > Arguments for final state 2:
> > > > 2a) The Source API itself seems already sort of following the unified
> > API
> > > > pattern.
> > > > 2b) There is no "programming time" method error check in SQL case, so
> > we
> > > > cannot really achieve final state 1 across the board.
> > > > 2c) It is an easier path given our current status, i.e. Table is
> > already
> > > > following final state 2.
> > > > 2d) Users can always explicitly check the boundedness if they want
> to.
> > > >
> > > > As I mentioned earlier, my initial thought was also to have a
> > > > "configuration based" Source rather than a "parameter based" Source.
> So
> > > it
> > > > is completely possible that I missed some important consideration or
> > > design
> > > > principles that we want to enforce for the project. It would be good
> > > > if @Stephan
> > > > Ewen <step...@ververica.com> and @Aljoscha Krettek <
> > > aljos...@ververica.com> can
> > > > also provide more thoughts on this.
> > > >
> > > >
> > > > Re: Jingsong
> > > >
> > > > As you said, there are some batched system source, like parquet/orc
> > > source.
> > > >> Could we have the batch emit interface to improve performance? The
> > > queue of
> > > >> per record may cause performance degradation.
> > > >
> > > >
> > > > The current interface does not necessarily cause performance problem
> > in a
> > > > multi-threading case. In fact, the base implementation allows
> > > SplitReaders
> > > > to add a batch <E> of records<T> to the records queue<E>, so each
> > element
> > > > in the records queue would be a batch <E>. In this case, when the
> main
> > > > thread polls records, it will take a batch <E> of records <T> from
> the
> > > > shared records queue and process the records <T> in a batch manner.
> > > >
> > > > Thanks,
> > > >
> > > > Jiangjie (Becket) Qin
> > > >
> > > > On Thu, Dec 12, 2019 at 1:29 PM Jingsong Li <jingsongl...@gmail.com>
> > > wrote:
> > > >
> > > >> Hi Becket,
> > > >>
> > > >> I also have some performance concerns too.
> > > >>
> > > >> If I understand correctly, SourceOutput will emit data per record
> into
> > > the
> > > >> queue? I'm worried about the multithreading performance of this
> queue.
> > > >>
> > > >>> One example is some batched messaging systems which only have an
> > offset
> > > >> for the entire batch instead of individual messages in the batch.
> > > >>
> > > >> As you said, there are some batched system source, like parquet/orc
> > > source.
> > > >> Could we have the batch emit interface to improve performance? The
> > > queue of
> > > >> per record may cause performance degradation.
> > > >>
> > > >> Best,
> > > >> Jingsong Lee
> > > >>
> > > >> On Thu, Dec 12, 2019 at 9:15 AM Jark Wu <imj...@gmail.com> wrote:
> > > >>
> > > >>> Hi Becket,
> > > >>>
> > > >>> I think Dawid explained things clearly and makes a lot of sense.
> > > >>> I'm also in favor of #2, because #1 doesn't work for our future
> > unified
> > > >>> envrionment.
> > > >>>
> > > >>> You can see the vision in this documentation [1]. In the future, we
> > > would
> > > >>> like to
> > > >>> drop the global streaming/batch mode in SQL (i.e.
> > > >>> EnvironmentSettings#inStreamingMode/inBatchMode).
> > > >>> A source is bounded or unbounded once defined, so queries can be
> > > inferred
> > > >>> from source to run
> > > >>> in streaming or batch or hybrid mode. However, in #1, we will lose
> > this
> > > >>> ability because the framework
> > > >>> doesn't know whether the source is bounded or unbounded.
> > > >>>
> > > >>> Best,
> > > >>> Jark
> > > >>>
> > > >>>
> > > >>> [1]:
> > > >>>
> > > >>>
> > > >>
> > >
> >
> https://docs.google.com/document/d/1yrKXEIRATfxHJJ0K3t6wUgXAtZq8D-XgvEnvl2uUcr0/edit#heading=h.v4ib17buma1p
> > > >>>
> > > >>> On Wed, 11 Dec 2019 at 20:52, Piotr Nowojski <pi...@ververica.com>
> > > >> wrote:
> > > >>>
> > > >>>> Hi,
> > > >>>>
> > > >>>> Regarding the:
> > > >>>>
> > > >>>> Collection<E> getNextRecords()
> > > >>>>
> > > >>>> I’m pretty sure such design would unfortunately impact the
> > performance
> > > >>>> (accessing and potentially creating the collection on the hot
> path).
> > > >>>>
> > > >>>> Also the
> > > >>>>
> > > >>>> InputStatus emitNext(DataOutput<T> output) throws Exception;
> > > >>>> or
> > > >>>> Status pollNext(SourceOutput<T> sourceOutput) throws Exception;
> > > >>>>
> > > >>>> Gives us some opportunities in the future, to allow Source hot
> > looping
> > > >>>> inside, until it receives some signal “please exit because of some
> > > >>> reasons”
> > > >>>> (output collector could return such hint upon collecting the
> > result).
> > > >> But
> > > >>>> that’s another topic outside of this FLIP’s scope.
> > > >>>>
> > > >>>> Piotrek
> > > >>>>
> > > >>>>> On 11 Dec 2019, at 10:41, Till Rohrmann <trohrm...@apache.org>
> > > >> wrote:
> > > >>>>>
> > > >>>>> Hi Becket,
> > > >>>>>
> > > >>>>> quick clarification from my side because I think you
> misunderstood
> > my
> > > >>>>> question. I did not suggest to let the SourceReader return only a
> > > >>> single
> > > >>>>> record at a time when calling getNextRecords. As the return type
> > > >>>> indicates,
> > > >>>>> the method can return an arbitrary number of records.
> > > >>>>>
> > > >>>>> Cheers,
> > > >>>>> Till
> > > >>>>>
> > > >>>>> On Wed, Dec 11, 2019 at 10:13 AM Dawid Wysakowicz <
> > > >>>> dwysakow...@apache.org <mailto:dwysakow...@apache.org>>
> > > >>>>> wrote:
> > > >>>>>
> > > >>>>>> Hi Becket,
> > > >>>>>>
> > > >>>>>> Issue #1 - Design of Source interface
> > > >>>>>>
> > > >>>>>> I mentioned the lack of a method like
> > > >>>> Source#createEnumerator(Boundedness
> > > >>>>>> boundedness, SplitEnumeratorContext context), because without
> the
> > > >>>> current
> > > >>>>>> proposal is not complete/does not work.
> > > >>>>>>
> > > >>>>>> If we say that boundedness is an intrinsic property of a source
> > imo
> > > >> we
> > > >>>>>> don't need the Source#createEnumerator(Boundedness boundedness,
> > > >>>>>> SplitEnumeratorContext context) method.
> > > >>>>>>
> > > >>>>>> Assuming a source from my previous example:
> > > >>>>>>
> > > >>>>>> Source source = KafkaSource.builder()
> > > >>>>>> ...
> > > >>>>>> .untilTimestamp(...)
> > > >>>>>> .build()
> > > >>>>>>
> > > >>>>>> Would the enumerator differ if created like
> > > >>>>>> source.createEnumerator(CONTINUOUS_UNBOUNDED, ...) vs source
> > > >>>>>> .createEnumerator(BOUNDED, ...)? I know I am repeating myself,
> but
> > > >>> this
> > > >>>> is
> > > >>>>>> the part that my opinion differ the most from the current
> > proposal.
> > > >> I
> > > >>>>>> really think it should always be the source that tells if it is
> > > >>> bounded
> > > >>>> or
> > > >>>>>> not. In the current proposal methods
> continousSource/boundedSource
> > > >>>> somewhat
> > > >>>>>> reconfigure the source, which I think is misleading.
> > > >>>>>>
> > > >>>>>> I think a call like:
> > > >>>>>>
> > > >>>>>> Source source = KafkaSource.builder()
> > > >>>>>> ...
> > > >>>>>> .readContinously() / readUntilLatestOffset() /
> > readUntilTimestamp
> > > /
> > > >>>> readUntilOffsets / ...
> > > >>>>>> .build()
> > > >>>>>>
> > > >>>>>> is way cleaner (and expressive) than
> > > >>>>>>
> > > >>>>>> Source source = KafkaSource.builder()
> > > >>>>>> ...
> > > >>>>>> .build()
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> env.continousSource(source) // which actually underneath would
> > call
> > > >>>> createEnumerator(CONTINUOUS, ctx) which would be equivalent to
> > > >>>> source.readContinously().createEnumerator(ctx)
> > > >>>>>> // or
> > > >>>>>> env.boundedSource(source) // which actually underneath would
> call
> > > >>>> createEnumerator(BOUNDED, ctx) which would be equivalent to
> > > >>>> source.readUntilLatestOffset().createEnumerator(ctx)
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> Sorry for the comparison, but to me it seems there is too much
> > magic
> > > >>>>>> happening underneath those two calls.
> > > >>>>>>
> > > >>>>>> I really believe the Source interface should have getBoundedness
> > > >>> method
> > > >>>>>> instead of (supportBoundedness) + createEnumerator(Boundedness,
> > ...)
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> Issue #2 - Design of
> > > >>>>>> ExecutionEnvironment#source()/continuousSource()/boundedSource()
> > > >>>>>>
> > > >>>>>> As you might have guessed I am slightly in favor of option #2
> > > >>> modified.
> > > >>>>>> Yes I am aware every step of the dag would have to be able to
> say
> > if
> > > >>> it
> > > >>>> is
> > > >>>>>> bounded or not. I have a feeling it would be easier to express
> > cross
> > > >>>>>> bounded/unbounded operations, but I must admit I have not
> thought
> > it
> > > >>>>>> through thoroughly, In the spirit of batch is just a special
> case
> > of
> > > >>>>>> streaming I thought BoundedStream would extend from DataStream.
> > > >>> Correct
> > > >>>> me
> > > >>>>>> if I am wrong. In such a setup the cross bounded/unbounded
> > operation
> > > >>>> could
> > > >>>>>> be expressed quite easily I think:
> > > >>>>>>
> > > >>>>>> DataStream {
> > > >>>>>> DataStream join(DataStream, ...); // we could not really tell
> if
> > > >> the
> > > >>>> result is bounded or not, but because bounded stream is a special
> > case
> > > >> of
> > > >>>> unbounded the API object is correct, irrespective if the left or
> > right
> > > >>> side
> > > >>>> of the join is bounded
> > > >>>>>> }
> > > >>>>>>
> > > >>>>>> BoundedStream extends DataStream {
> > > >>>>>> BoundedStream join(BoundedStream, ...); // only if both sides
> > are
> > > >>>> bounded the result can be bounded as well. However we do have
> access
> > > to
> > > >>> the
> > > >>>> DataStream#join here, so you can still join with a DataStream
> > > >>>>>> }
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> On the other hand I also see benefits of two completely
> disjointed
> > > >>> APIs,
> > > >>>>>> as we could prohibit some streaming calls in the bounded API. I
> > > >> can't
> > > >>>> think
> > > >>>>>> of any unbounded operators that could not be implemented for
> > bounded
> > > >>>> stream.
> > > >>>>>>
> > > >>>>>> Besides I think we both agree we don't like the method:
> > > >>>>>>
> > > >>>>>> DataStream boundedStream(Source)
> > > >>>>>>
> > > >>>>>> suggested in the current state of the FLIP. Do we ? :)
> > > >>>>>>
> > > >>>>>> Best,
> > > >>>>>>
> > > >>>>>> Dawid
> > > >>>>>>
> > > >>>>>> On 10/12/2019 18:57, Becket Qin wrote:
> > > >>>>>>
> > > >>>>>> Hi folks,
> > > >>>>>>
> > > >>>>>> Thanks for the discussion, great feedback. Also thanks Dawid for
> > the
> > > >>>>>> explanation, it is much clearer now.
> > > >>>>>>
> > > >>>>>> One thing that is indeed missing from the FLIP is how the
> > > >> boundedness
> > > >>> is
> > > >>>>>> passed to the Source implementation. So the API should be
> > > >>>>>> Source#createEnumerator(Boundedness boundedness,
> > > >>> SplitEnumeratorContext
> > > >>>>>> context)
> > > >>>>>> And we can probably remove the
> > Source#supportBoundedness(Boundedness
> > > >>>>>> boundedness) method.
> > > >>>>>>
> > > >>>>>> Assuming we have that, we are essentially choosing from one of
> the
> > > >>>>>> following two options:
> > > >>>>>>
> > > >>>>>> Option 1:
> > > >>>>>> // The source is continuous source, and only unbounded
> operations
> > > >> can
> > > >>> be
> > > >>>>>> performed.
> > > >>>>>> DataStream<Type> datastream = env.continuousSource(someSource);
> > > >>>>>>
> > > >>>>>> // The source is bounded source, both bounded and unbounded
> > > >> operations
> > > >>>> can
> > > >>>>>> be performed.
> > > >>>>>> BoundedDataStream<Type> boundedDataStream =
> > > >>>> env.boundedSource(someSource);
> > > >>>>>>
> > > >>>>>> - Pros:
> > > >>>>>> a) explicit boundary between bounded / unbounded streams,
> > it
> > > >> is
> > > >>>>>> quite simple and clear to the users.
> > > >>>>>> - Cons:
> > > >>>>>> a) For applications that do not involve bounded
> operations,
> > > >> they
> > > >>>>>> still have to call different API to distinguish bounded /
> > unbounded
> > > >>>> streams.
> > > >>>>>> b) No support for bounded stream to run in a streaming
> > > runtime
> > > >>>>>> setting, i.e. scheduling and operators behaviors.
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> Option 2:
> > > >>>>>> // The source is either bounded or unbounded, but only unbounded
> > > >>>> operations
> > > >>>>>> could be performed on the returned DataStream.
> > > >>>>>> DataStream<Type> dataStream = env.source(someSource);
> > > >>>>>>
> > > >>>>>> // The source must be a bounded source, otherwise exception is
> > > >> thrown.
> > > >>>>>> BoundedDataStream<Type> boundedDataStream =
> > > >>>>>> env.boundedSource(boundedSource);
> > > >>>>>>
> > > >>>>>> The pros and cons are exactly the opposite of option 1.
> > > >>>>>> - Pros:
> > > >>>>>> a) For applications that do not involve bounded
> operations,
> > > >> they
> > > >>>>>> still have to call different API to distinguish bounded /
> > unbounded
> > > >>>> streams.
> > > >>>>>> b) Support for bounded stream to run in a streaming
> runtime
> > > >>>> setting,
> > > >>>>>> i.e. scheduling and operators behaviors.
> > > >>>>>> - Cons:
> > > >>>>>> a) Bounded / unbounded streams are kind of mixed, i.e.
> > given
> > > a
> > > >>>>>> DataStream, it is not clear whether it is bounded or not, unless
> > you
> > > >>>> have
> > > >>>>>> the access to its source.
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> If we only think from the Source API perspective, option 2
> seems a
> > > >>>> better
> > > >>>>>> choice because functionality wise it is a superset of option 1,
> at
> > > >> the
> > > >>>> cost
> > > >>>>>> of some seemingly acceptable ambiguity in the DataStream API.
> > > >>>>>> But if we look at the DataStream API as a whole, option 1 seems
> a
> > > >>>> clearer
> > > >>>>>> choice. For example, some times a library may have to know
> > whether a
> > > >>>>>> certain task will finish or not. And it would be difficult to
> tell
> > > >> if
> > > >>>> the
> > > >>>>>> input is a DataStream, unless additional information is provided
> > all
> > > >>> the
> > > >>>>>> way from the Source. One possible solution is to have a
> *modified
> > > >>>> option 2*
> > > >>>>>> which adds a method to the DataStream API to indicate
> boundedness,
> > > >>> such
> > > >>>> as
> > > >>>>>> getBoundedness(). It would solve the problem with a potential
> > > >>> confusion
> > > >>>> of
> > > >>>>>> what is difference between a DataStream with
> getBoundedness()=true
> > > >>> and a
> > > >>>>>> BoundedDataStream. But that seems not super difficult to
> explain.
> > > >>>>>>
> > > >>>>>> So from API's perspective, I don't have a strong opinion between
> > > >>>> *option 1*
> > > >>>>>> and *modified option 2. *I like the cleanness of option 1, but
> > > >>> modified
> > > >>>>>> option 2 would be more attractive if we have concrete use case
> for
> > > >> the
> > > >>>>>> "Bounded stream with unbounded streaming runtime settings".
> > > >>>>>>
> > > >>>>>> Re: Till
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> Maybe this has already been asked before but I was wondering why
> > the
> > > >>>>>> SourceReader interface has the method pollNext which hands the
> > > >>>>>> responsibility of outputting elements to the SourceReader
> > > >>>> implementation?
> > > >>>>>> Has this been done for backwards compatibility reasons with the
> > old
> > > >>>> source
> > > >>>>>> interface? If not, then one could define a Collection<E>
> > > >>>> getNextRecords()
> > > >>>>>> method which returns the currently retrieved records and then
> the
> > > >>> caller
> > > >>>>>> emits them outside of the SourceReader. That way the interface
> > would
> > > >>> not
> > > >>>>>> allow to implement an outputting loop where we never hand back
> > > >> control
> > > >>>> to
> > > >>>>>> the caller. At the moment, this contract can be easily broken
> and
> > is
> > > >>>> only
> > > >>>>>> mentioned loosely in the JavaDocs.
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> The primary reason we handover the SourceOutput to the
> > SourceReader
> > > >> is
> > > >>>>>> because sometimes it is difficult for a SourceReader to emit one
> > > >>> record
> > > >>>> at
> > > >>>>>> a time. One example is some batched messaging systems which only
> > > >> have
> > > >>> an
> > > >>>>>> offset for the entire batch instead of individual messages in
> the
> > > >>>> batch. In
> > > >>>>>> that case, returning one record at a time would leave the
> > > >> SourceReader
> > > >>>> in
> > > >>>>>> an uncheckpointable state because they can only checkpoint at
> the
> > > >>> batch
> > > >>>>>> boundaries.
> > > >>>>>>
> > > >>>>>> Thanks,
> > > >>>>>>
> > > >>>>>> Jiangjie (Becket) Qin
> > > >>>>>>
> > > >>>>>> On Tue, Dec 10, 2019 at 5:33 PM Till Rohrmann <
> > trohrm...@apache.org
> > > >>>> <mailto:trohrm...@apache.org>> <trohrm...@apache.org <mailto:
> > > >>>> trohrm...@apache.org>> wrote:
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> Hi everyone,
> > > >>>>>>
> > > >>>>>> thanks for drafting this FLIP. It reads very well.
> > > >>>>>>
> > > >>>>>> Concerning Dawid's proposal, I tend to agree. The boundedness
> > could
> > > >>> come
> > > >>>>>> from the source and tell the system how to treat the operator
> > > >>>> (scheduling
> > > >>>>>> wise). From a user's perspective it should be fine to get back a
> > > >>>> DataStream
> > > >>>>>> when calling env.source(boundedSource) if he does not need
> special
> > > >>>>>> operations defined on a BoundedDataStream. If he needs this,
> then
> > > >> one
> > > >>>> could
> > > >>>>>> use the method BoundedDataStream
> env.boundedSource(boundedSource).
> > > >>>>>>
> > > >>>>>> If possible, we could enforce the proper usage of
> > > >> env.boundedSource()
> > > >>> by
> > > >>>>>> introducing a BoundedSource type so that one cannot pass an
> > > >>>>>> unbounded source to it. That way users would not be able to
> shoot
> > > >>>>>> themselves in the foot.
> > > >>>>>>
> > > >>>>>> Maybe this has already been asked before but I was wondering why
> > the
> > > >>>>>> SourceReader interface has the method pollNext which hands the
> > > >>>>>> responsibility of outputting elements to the SourceReader
> > > >>>> implementation?
> > > >>>>>> Has this been done for backwards compatibility reasons with the
> > old
> > > >>>> source
> > > >>>>>> interface? If not, then one could define a Collection<E>
> > > >>>> getNextRecords()
> > > >>>>>> method which returns the currently retrieved records and then
> the
> > > >>> caller
> > > >>>>>> emits them outside of the SourceReader. That way the interface
> > would
> > > >>> not
> > > >>>>>> allow to implement an outputting loop where we never hand back
> > > >> control
> > > >>>> to
> > > >>>>>> the caller. At the moment, this contract can be easily broken
> and
> > is
> > > >>>> only
> > > >>>>>> mentioned loosely in the JavaDocs.
> > > >>>>>>
> > > >>>>>> Cheers,
> > > >>>>>> Till
> > > >>>>>>
> > > >>>>>> On Tue, Dec 10, 2019 at 7:49 AM Jingsong Li <
> > jingsongl...@gmail.com
> > > >>>> <mailto:jingsongl...@gmail.com>> <jingsongl...@gmail.com <mailto:
> > > >>>> jingsongl...@gmail.com>>
> > > >>>>>> wrote:
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> Hi all,
> > > >>>>>>
> > > >>>>>> I think current design is good.
> > > >>>>>>
> > > >>>>>> My understanding is:
> > > >>>>>>
> > > >>>>>> For execution mode: bounded mode and continuous mode, It's
> totally
> > > >>>>>> different. I don't think we have the ability to integrate the
> two
> > > >>> models
> > > >>>>>>
> > > >>>>>> at
> > > >>>>>>
> > > >>>>>> present. It's about scheduling, memory, algorithms, States, etc.
> > we
> > > >>>>>> shouldn't confuse them.
> > > >>>>>>
> > > >>>>>> For source capabilities: only bounded, only continuous, both
> > bounded
> > > >>> and
> > > >>>>>> continuous.
> > > >>>>>> I think Kafka is a source that can be ran both bounded
> > > >>>>>> and continuous execution mode.
> > > >>>>>> And Kafka with end offset should be ran both bounded
> > > >>>>>> and continuous execution mode. Using apache Beam with Flink
> > > >> runner, I
> > > >>>>>>
> > > >>>>>> used
> > > >>>>>>
> > > >>>>>> to run a "bounded" Kafka in streaming mode. For our previous
> > > >>> DataStream,
> > > >>>>>>
> > > >>>>>> it
> > > >>>>>>
> > > >>>>>> is not necessarily required that the source cannot be bounded.
> > > >>>>>>
> > > >>>>>> So it is my thought for Dawid's question:
> > > >>>>>> 1.pass a bounded source to continuousSource() +1
> > > >>>>>> 2.pass a continuous source to boundedSource() -1, should throw
> > > >>>> exception.
> > > >>>>>>
> > > >>>>>> In StreamExecutionEnvironment, continuousSource and
> boundedSource
> > > >>> define
> > > >>>>>> the execution mode. It defines a clear boundary of execution
> mode.
> > > >>>>>>
> > > >>>>>> Best,
> > > >>>>>> Jingsong Lee
> > > >>>>>>
> > > >>>>>> On Tue, Dec 10, 2019 at 10:37 AM Jark Wu <imj...@gmail.com
> > <mailto:
> > > >>>> imj...@gmail.com>> <imj...@gmail.com <mailto:imj...@gmail.com>>
> > > wrote:
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> I agree with Dawid's point that the boundedness information
> should
> > > >>> come
> > > >>>>>> from the source itself (e.g. the end timestamp), not through
> > > >>>>>> env.boundedSouce()/continuousSource().
> > > >>>>>> I think if we want to support something like `env.source()` that
> > > >>> derive
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> execution mode from source, `supportsBoundedness(Boundedness)`
> > > >>>>>> method is not enough, because we don't know whether it is
> bounded
> > or
> > > >>>>>>
> > > >>>>>> not.
> > > >>>>>>
> > > >>>>>> Best,
> > > >>>>>> Jark
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> On Mon, 9 Dec 2019 at 22:21, Dawid Wysakowicz <
> > > >> dwysakow...@apache.org
> > > >>>> <mailto:dwysakow...@apache.org>> <dwysakow...@apache.org <mailto:
> > > >>>> dwysakow...@apache.org>>
> > > >>>>>> wrote:
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> One more thing. In the current proposal, with the
> > > >>>>>> supportsBoundedness(Boundedness) method and the boundedness
> coming
> > > >>>>>>
> > > >>>>>> from
> > > >>>>>>
> > > >>>>>> either continuousSource or boundedSource I could not find how
> this
> > > >>>>>> information is fed back to the SplitEnumerator.
> > > >>>>>>
> > > >>>>>> Best,
> > > >>>>>>
> > > >>>>>> Dawid
> > > >>>>>>
> > > >>>>>> On 09/12/2019 13:52, Becket Qin wrote:
> > > >>>>>>
> > > >>>>>> Hi Dawid,
> > > >>>>>>
> > > >>>>>> Thanks for the comments. This actually brings another relevant
> > > >>>>>>
> > > >>>>>> question
> > > >>>>>>
> > > >>>>>> about what does a "bounded source" imply. I actually had the
> same
> > > >>>>>> impression when I look at the Source API. Here is what I
> > understand
> > > >>>>>>
> > > >>>>>> after
> > > >>>>>>
> > > >>>>>> some discussion with Stephan. The bounded source has the
> following
> > > >>>>>>
> > > >>>>>> impacts.
> > > >>>>>>
> > > >>>>>> 1. API validity.
> > > >>>>>> - A bounded source generates a bounded stream so some operations
> > > >>>>>>
> > > >>>>>> that
> > > >>>>>>
> > > >>>>>> only
> > > >>>>>>
> > > >>>>>> works for bounded records would be performed, e.g. sort.
> > > >>>>>> - To expose these bounded stream only APIs, there are two
> options:
> > > >>>>>> a. Add them to the DataStream API and throw exception if a
> > > >>>>>>
> > > >>>>>> method
> > > >>>>>>
> > > >>>>>> is
> > > >>>>>>
> > > >>>>>> called on an unbounded stream.
> > > >>>>>> b. Create a BoundedDataStream class which is returned from
> > > >>>>>> env.boundedSource(), while DataStream is returned from
> > > >>>>>>
> > > >>>>>> env.continousSource().
> > > >>>>>>
> > > >>>>>> Note that this cannot be done by having single
> > > >>>>>>
> > > >>>>>> env.source(theSource)
> > > >>>>>>
> > > >>>>>> even
> > > >>>>>>
> > > >>>>>> the Source has a getBoundedness() method.
> > > >>>>>>
> > > >>>>>> 2. Scheduling
> > > >>>>>> - A bounded source could be computed stage by stage without
> > > >>>>>>
> > > >>>>>> bringing
> > > >>>>>>
> > > >>>>>> up
> > > >>>>>>
> > > >>>>>> all
> > > >>>>>>
> > > >>>>>> the tasks at the same time.
> > > >>>>>>
> > > >>>>>> 3. Operator behaviors
> > > >>>>>> - A bounded source indicates the records are finite so some
> > > >>>>>>
> > > >>>>>> operators
> > > >>>>>>
> > > >>>>>> can
> > > >>>>>>
> > > >>>>>> wait until it receives all the records before it starts the
> > > >>>>>>
> > > >>>>>> processing.
> > > >>>>>>
> > > >>>>>> In the above impact, only 1 is relevant to the API design. And
> the
> > > >>>>>>
> > > >>>>>> current
> > > >>>>>>
> > > >>>>>> proposal in FLIP-27 is following 1.b.
> > > >>>>>>
> > > >>>>>> // boundedness depends of source property, imo this should
> always
> > > >>>>>>
> > > >>>>>> be
> > > >>>>>>
> > > >>>>>> preferred
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> DataStream<MyType> stream = env.source(theSource);
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> In your proposal, does DataStream have bounded stream only
> > methods?
> > > >>>>>>
> > > >>>>>> It
> > > >>>>>>
> > > >>>>>> looks it should have, otherwise passing a bounded Source to
> > > >>>>>>
> > > >>>>>> env.source()
> > > >>>>>>
> > > >>>>>> would be confusing. In that case, we will essentially do 1.a if
> an
> > > >>>>>> unbounded Source is created from env.source(unboundedSource).
> > > >>>>>>
> > > >>>>>> If we have the methods only supported for bounded streams in
> > > >>>>>>
> > > >>>>>> DataStream,
> > > >>>>>>
> > > >>>>>> it
> > > >>>>>>
> > > >>>>>> seems a little weird to have a separate BoundedDataStream
> > > >>>>>>
> > > >>>>>> interface.
> > > >>>>>>
> > > >>>>>> Am I understand it correctly?
> > > >>>>>>
> > > >>>>>> Thanks,
> > > >>>>>>
> > > >>>>>> Jiangjie (Becket) Qin
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> On Mon, Dec 9, 2019 at 6:40 PM Dawid Wysakowicz <
> > > >>>>>>
> > > >>>>>> dwysakow...@apache.org <mailto:dwysakow...@apache.org>>
> > > >>>>>>
> > > >>>>>> wrote:
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> Hi all,
> > > >>>>>>
> > > >>>>>> Really well written proposal and very important one. I must
> admit
> > > >>>>>>
> > > >>>>>> I
> > > >>>>>>
> > > >>>>>> have
> > > >>>>>>
> > > >>>>>> not understood all the intricacies of it yet.
> > > >>>>>>
> > > >>>>>> One question I have though is about where does the information
> > > >>>>>>
> > > >>>>>> about
> > > >>>>>>
> > > >>>>>> boundedness come from. I think in most cases it is a property of
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> source. As you described it might be e.g. end offset, a flag
> > > >>>>>>
> > > >>>>>> should
> > > >>>>>>
> > > >>>>>> it
> > > >>>>>>
> > > >>>>>> monitor new splits etc. I think it would be a really nice use
> case
> > > >>>>>>
> > > >>>>>> to
> > > >>>>>>
> > > >>>>>> be
> > > >>>>>>
> > > >>>>>> able to say:
> > > >>>>>>
> > > >>>>>> new KafkaSource().readUntil(long timestamp),
> > > >>>>>>
> > > >>>>>> which could work as an "end offset". Moreover I think all
> Bounded
> > > >>>>>>
> > > >>>>>> sources
> > > >>>>>>
> > > >>>>>> support continuous mode, but no intrinsically continuous source
> > > >>>>>>
> > > >>>>>> support
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> Bounded mode. If I understood the proposal correctly it suggest
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> boundedness sort of "comes" from the outside of the source, from
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> invokation of either boundedStream or continousSource.
> > > >>>>>>
> > > >>>>>> I am wondering if it would make sense to actually change the
> > > >>>>>>
> > > >>>>>> method
> > > >>>>>>
> > > >>>>>> boolean Source#supportsBoundedness(Boundedness)
> > > >>>>>>
> > > >>>>>> to
> > > >>>>>>
> > > >>>>>> Boundedness Source#getBoundedness().
> > > >>>>>>
> > > >>>>>> As for the methods #boundedSource, #continousSource, assuming
> the
> > > >>>>>> boundedness is property of the source they do not affect how the
> > > >>>>>>
> > > >>>>>> enumerator
> > > >>>>>>
> > > >>>>>> works, but mostly how the dag is scheduled, right? I am not
> > > >>>>>>
> > > >>>>>> against
> > > >>>>>>
> > > >>>>>> those
> > > >>>>>>
> > > >>>>>> methods, but I think it is a very specific use case to actually
> > > >>>>>>
> > > >>>>>> override
> > > >>>>>>
> > > >>>>>> the property of the source. In general I would expect users to
> > > >>>>>>
> > > >>>>>> only
> > > >>>>>>
> > > >>>>>> call
> > > >>>>>>
> > > >>>>>> env.source(theSource), where the source tells if it is bounded
> or
> > > >>>>>>
> > > >>>>>> not. I
> > > >>>>>>
> > > >>>>>> would suggest considering following set of methods:
> > > >>>>>>
> > > >>>>>> // boundedness depends of source property, imo this should
> always
> > > >>>>>>
> > > >>>>>> be
> > > >>>>>>
> > > >>>>>> preferred
> > > >>>>>>
> > > >>>>>> DataStream<MyType> stream = env.source(theSource);
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> // always continous execution, whether bounded or unbounded
> source
> > > >>>>>>
> > > >>>>>> DataStream<MyType> boundedStream =
> env.continousSource(theSource);
> > > >>>>>>
> > > >>>>>> // imo this would make sense if the BoundedDataStream provides
> > > >>>>>>
> > > >>>>>> additional features unavailable for continous mode
> > > >>>>>>
> > > >>>>>> BoundedDataStream<MyType> batch = env.boundedSource(theSource);
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> Best,
> > > >>>>>>
> > > >>>>>> Dawid
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> On 04/12/2019 11:25, Stephan Ewen wrote:
> > > >>>>>>
> > > >>>>>> Thanks, Becket, for updating this.
> > > >>>>>>
> > > >>>>>> I agree with moving the aspects you mentioned into separate
> FLIPs
> > > >>>>>>
> > > >>>>>> -
> > > >>>>>>
> > > >>>>>> this
> > > >>>>>>
> > > >>>>>> one way becoming unwieldy in size.
> > > >>>>>>
> > > >>>>>> +1 to the FLIP in its current state. Its a very detailed
> write-up,
> > > >>>>>>
> > > >>>>>> nicely
> > > >>>>>>
> > > >>>>>> done!
> > > >>>>>>
> > > >>>>>> On Wed, Dec 4, 2019 at 7:38 AM Becket Qin <becket....@gmail.com
> > > >>>> <mailto:becket....@gmail.com>> <becket....@gmail.com <mailto:
> > > >>>> becket....@gmail.com>>
> > > >>>>>>
> > > >>>>>> <
> > > >>>>>>
> > > >>>>>> becket....@gmail.com <mailto:becket....@gmail.com>> wrote:
> > > >>>>>>
> > > >>>>>> Hi all,
> > > >>>>>>
> > > >>>>>> Sorry for the long belated update. I have updated FLIP-27 wiki
> > > >>>>>>
> > > >>>>>> page
> > > >>>>>>
> > > >>>>>> with
> > > >>>>>>
> > > >>>>>> the latest proposals. Some noticeable changes include:
> > > >>>>>> 1. A new generic communication mechanism between SplitEnumerator
> > > >>>>>>
> > > >>>>>> and
> > > >>>>>>
> > > >>>>>> SourceReader.
> > > >>>>>> 2. Some detail API method signature changes.
> > > >>>>>>
> > > >>>>>> We left a few things out of this FLIP and will address them in
> > > >>>>>>
> > > >>>>>> separate
> > > >>>>>>
> > > >>>>>> FLIPs. Including:
> > > >>>>>> 1. Per split event time.
> > > >>>>>> 2. Event time alignment.
> > > >>>>>> 3. Fine grained failover for SplitEnumerator failure.
> > > >>>>>>
> > > >>>>>> Please let us know if you have any question.
> > > >>>>>>
> > > >>>>>> Thanks,
> > > >>>>>>
> > > >>>>>> Jiangjie (Becket) Qin
> > > >>>>>>
> > > >>>>>> On Sat, Nov 16, 2019 at 6:10 AM Stephan Ewen <se...@apache.org
> > > >>> <mailto:
> > > >>>> se...@apache.org>> <se...@apache.org <mailto:se...@apache.org>> <
> > > >>>>>>
> > > >>>>>> se...@apache.org <mailto:se...@apache.org>> wrote:
> > > >>>>>>
> > > >>>>>> Hi Łukasz!
> > > >>>>>>
> > > >>>>>> Becket and me are working hard on figuring out the last details
> > > >>>>>>
> > > >>>>>> and
> > > >>>>>>
> > > >>>>>> implementing the first PoC. We would update the FLIP hopefully
> > > >>>>>>
> > > >>>>>> next
> > > >>>>>>
> > > >>>>>> week.
> > > >>>>>>
> > > >>>>>> There is a fair chance that a first version of this will be in
> > > >>>>>>
> > > >>>>>> 1.10,
> > > >>>>>>
> > > >>>>>> but
> > > >>>>>>
> > > >>>>>> I
> > > >>>>>>
> > > >>>>>> think it will take another release to battle test it and migrate
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> connectors.
> > > >>>>>>
> > > >>>>>> Best,
> > > >>>>>> Stephan
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> On Fri, Nov 15, 2019 at 11:14 AM Łukasz Jędrzejewski <
> l...@touk.pl
> > > >>>> <mailto:l...@touk.pl>
> > > >>>>>>
> > > >>>>>> <
> > > >>>>>>
> > > >>>>>> l...@touk.pl <mailto:l...@touk.pl>>
> > > >>>>>>
> > > >>>>>> wrote:
> > > >>>>>>
> > > >>>>>> Hi,
> > > >>>>>>
> > > >>>>>> This proposal looks very promising for us. Do you have any plans
> > > >>>>>>
> > > >>>>>> in
> > > >>>>>>
> > > >>>>>> which
> > > >>>>>>
> > > >>>>>> Flink release it is going to be released? We are thinking on
> > > >>>>>>
> > > >>>>>> using a
> > > >>>>>>
> > > >>>>>> Data
> > > >>>>>>
> > > >>>>>> Set API for our future use cases but on the other hand Data Set
> > > >>>>>>
> > > >>>>>> API
> > > >>>>>>
> > > >>>>>> is
> > > >>>>>>
> > > >>>>>> going to be deprecated so using proposed bounded data streams
> > > >>>>>>
> > > >>>>>> solution
> > > >>>>>>
> > > >>>>>> could be more viable in the long term.
> > > >>>>>>
> > > >>>>>> Thanks,
> > > >>>>>> Łukasz
> > > >>>>>>
> > > >>>>>> On 2019/10/01 15:48:03, Thomas Weise <thomas.we...@gmail.com
> > > >> <mailto:
> > > >>>> thomas.we...@gmail.com>> <thomas.we...@gmail.com <mailto:
> > > >>>> thomas.we...@gmail.com>> <
> > > >>>>>>
> > > >>>>>> thomas.we...@gmail.com <mailto:thomas.we...@gmail.com>> wrote:
> > > >>>>>>
> > > >>>>>> Thanks for putting together this proposal!
> > > >>>>>>
> > > >>>>>> I see that the "Per Split Event Time" and "Event Time Alignment"
> > > >>>>>>
> > > >>>>>> sections
> > > >>>>>>
> > > >>>>>> are still TBD.
> > > >>>>>>
> > > >>>>>> It would probably be good to flesh those out a bit before
> > > >>>>>>
> > > >>>>>> proceeding
> > > >>>>>>
> > > >>>>>> too
> > > >>>>>>
> > > >>>>>> far
> > > >>>>>>
> > > >>>>>> as the event time alignment will probably influence the
> > > >>>>>>
> > > >>>>>> interaction
> > > >>>>>>
> > > >>>>>> with
> > > >>>>>>
> > > >>>>>> the split reader, specifically ReaderStatus
> > > >>>>>>
> > > >>>>>> emitNext(SourceOutput<E>
> > > >>>>>>
> > > >>>>>> output).
> > > >>>>>>
> > > >>>>>> We currently have only one implementation for event time
> alignment
> > > >>>>>>
> > > >>>>>> in
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> Kinesis consumer. The synchronization in that case takes place
> as
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> last
> > > >>>>>>
> > > >>>>>> step before records are emitted downstream (RecordEmitter). With
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> currently proposed interfaces, the equivalent can be implemented
> > > >>>>>>
> > > >>>>>> in
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> reader loop, although note that in the Kinesis consumer the per
> > > >>>>>>
> > > >>>>>> shard
> > > >>>>>>
> > > >>>>>> threads push records.
> > > >>>>>>
> > > >>>>>> Synchronization has not been implemented for the Kafka consumer
> > > >>>>>>
> > > >>>>>> yet.
> > > >>>>>>
> > > >>>>>> https://issues.apache.org/jira/browse/FLINK-12675 <
> > > >>>> https://issues.apache.org/jira/browse/FLINK-12675>
> > > >>>>>>
> > > >>>>>> When I looked at it, I realized that the implementation will
> look
> > > >>>>>>
> > > >>>>>> quite
> > > >>>>>>
> > > >>>>>> different
> > > >>>>>> from Kinesis because it needs to take place in the pull part,
> > > >>>>>>
> > > >>>>>> where
> > > >>>>>>
> > > >>>>>> records
> > > >>>>>>
> > > >>>>>> are taken from the Kafka client. Due to the multiplexing it
> cannot
> > > >>>>>>
> > > >>>>>> be
> > > >>>>>>
> > > >>>>>> done
> > > >>>>>>
> > > >>>>>> by blocking the split thread like it currently works for
> Kinesis.
> > > >>>>>>
> > > >>>>>> Reading
> > > >>>>>>
> > > >>>>>> from individual Kafka partitions needs to be controlled via
> > > >>>>>>
> > > >>>>>> pause/resume
> > > >>>>>>
> > > >>>>>> on the Kafka client.
> > > >>>>>>
> > > >>>>>> To take on that responsibility the split thread would need to be
> > > >>>>>>
> > > >>>>>> aware
> > > >>>>>>
> > > >>>>>> of
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>> watermarks or at least whether it should or should not continue
> to
> > > >>>>>>
> > > >>>>>> consume
> > > >>>>>>
> > > >>>>>> a given split and this may require a different SourceReader or
> > > >>>>>>
> > > >>>>>> SourceOutput
> > > >>>>>>
> > > >>>>>> interface.
> > > >>>>>>
> > > >>>>>> Thanks,
> > > >>>>>> Thomas
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> On Fri, Jul 26, 2019 at 1:39 AM Biao Liu <mmyy1...@gmail.com
> > > >> <mailto:
> > > >>>> mmyy1...@gmail.com>> <mmyy1...@gmail.com <mailto:
> mmyy1...@gmail.com
> > >>
> > > >> <
> > > >>>>>>
> > > >>>>>> mmyy1...@gmail.com <mailto:mmyy1...@gmail.com>> wrote:
> > > >>>>>>
> > > >>>>>> Hi Stephan,
> > > >>>>>>
> > > >>>>>> Thank you for feedback!
> > > >>>>>> Will take a look at your branch before public discussing.
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> On Fri, Jul 26, 2019 at 12:01 AM Stephan Ewen <se...@apache.org
> > > >>>> <mailto:se...@apache.org>> <se...@apache.org <mailto:
> > se...@apache.org
> > > >>>>
> > > >>>>>>
> > > >>>>>> <
> > > >>>>>>
> > > >>>>>> se...@apache.org <mailto:se...@apache.org>>
> > > >>>>>>
> > > >>>>>> wrote:
> > > >>>>>>
> > > >>>>>> Hi Biao!
> > > >>>>>>
> > > >>>>>> Thanks for reviving this. I would like to join this discussion,
> > > >>>>>>
> > > >>>>>> but
> > > >>>>>>
> > > >>>>>> am
> > > >>>>>>
> > > >>>>>> quite occupied with the 1.9 release, so can we maybe pause this
> > > >>>>>>
> > > >>>>>> discussion
> > > >>>>>>
> > > >>>>>> for a week or so?
> > > >>>>>>
> > > >>>>>> In the meantime I can share some suggestion based on prior
> > > >>>>>>
> > > >>>>>> experiments:
> > > >>>>>>
> > > >>>>>> How to do watermarks / timestamp extractors in a simpler and
> more
> > > >>>>>>
> > > >>>>>> flexible
> > > >>>>>>
> > > >>>>>> way. I think that part is quite promising should be part of the
> > > >>>>>>
> > > >>>>>> new
> > > >>>>>>
> > > >>>>>> source
> > > >>>>>>
> > > >>>>>> interface.
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>
> > > >>>
> > > >>
> > >
> >
> https://github.com/StephanEwen/flink/tree/source_interface/flink-core/src/main/java/org/apache/flink/api/common/eventtime
> > > >>>> <
> > > >>>>
> > > >>>
> > > >>
> > >
> >
> https://github.com/StephanEwen/flink/tree/source_interface/flink-core/src/main/java/org/apache/flink/api/common/eventtime
> > > >>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>
> > > >>>
> > > >>
> > >
> >
> https://github.com/StephanEwen/flink/blob/source_interface/flink-core/src/main/java/org/apache/flink/api/common/src/SourceOutput.java
> > > >>>> <
> > > >>>>
> > > >>>
> > > >>
> > >
> >
> https://github.com/StephanEwen/flink/blob/source_interface/flink-core/src/main/java/org/apache/flink/api/common/src/SourceOutput.java
> > > >>>>>
> > > >>>>>>
> > > >>>>>> Some experiments on how to build the source reader and its
> > > >>>>>>
> > > >>>>>> library
> > > >>>>>>
> > > >>>>>> for
> > > >>>>>>
> > > >>>>>> common threading/split patterns:
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>
> > > >>>
> > > >>
> > >
> >
> https://github.com/StephanEwen/flink/tree/source_interface/flink-core/src/main/java/org/apache/flink/api/common/src
> > > >>>> <
> > > >>>>
> > > >>>
> > > >>
> > >
> >
> https://github.com/StephanEwen/flink/tree/source_interface/flink-core/src/main/java/org/apache/flink/api/common/src
> > > >>>>>
> > > >>>>>>
> > > >>>>>> Best,
> > > >>>>>> Stephan
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> On Thu, Jul 25, 2019 at 10:03 AM Biao Liu <mmyy1...@gmail.com
> > > >>> <mailto:
> > > >>>> mmyy1...@gmail.com>> <mmyy1...@gmail.com <mailto:
> mmyy1...@gmail.com
> > >>
> > > >> <
> > > >>>>>>
> > > >>>>>> mmyy1...@gmail.com <mailto:mmyy1...@gmail.com>>
> > > >>>>>>
> > > >>>>>> wrote:
> > > >>>>>>
> > > >>>>>> Hi devs,
> > > >>>>>>
> > > >>>>>> Since 1.9 is nearly released, I think we could get back to
> > > >>>>>>
> > > >>>>>> FLIP-27.
> > > >>>>>>
> > > >>>>>> I
> > > >>>>>>
> > > >>>>>> believe it should be included in 1.10.
> > > >>>>>>
> > > >>>>>> There are so many things mentioned in document of FLIP-27. [1] I
> > > >>>>>>
> > > >>>>>> think
> > > >>>>>>
> > > >>>>>> we'd better discuss them separately. However the wiki is not a
> > > >>>>>>
> > > >>>>>> good
> > > >>>>>>
> > > >>>>>> place
> > > >>>>>>
> > > >>>>>> to discuss. I wrote google doc about SplitReader API which
> > > >>>>>>
> > > >>>>>> misses
> > > >>>>>>
> > > >>>>>> some
> > > >>>>>>
> > > >>>>>> details in the document. [2]
> > > >>>>>>
> > > >>>>>> 1.
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>
> > > >>>
> > > >>
> > >
> >
> https://cwiki.apache.org/confluence/display/FLINK/FLIP-27:+Refactor+Source+Interface
> > > >>>> <
> > > >>>>
> > > >>>
> > > >>
> > >
> >
> https://cwiki.apache.org/confluence/display/FLINK/FLIP-27:+Refactor+Source+Interface
> > > >>>>>
> > > >>>>>>
> > > >>>>>> 2.
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>
> > > >>>
> > > >>
> > >
> >
> https://docs.google.com/document/d/1R1s_89T4S3CZwq7Tf31DciaMCqZwrLHGZFqPASu66oE/edit?usp=sharing
> > > >>>> <
> > > >>>>
> > > >>>
> > > >>
> > >
> >
> https://docs.google.com/document/d/1R1s_89T4S3CZwq7Tf31DciaMCqZwrLHGZFqPASu66oE/edit?usp=sharing
> > > >>>>>
> > > >>>>>>
> > > >>>>>> CC Stephan, Aljoscha, Piotrek, Becket
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> On Thu, Mar 28, 2019 at 4:38 PM Biao Liu <mmyy1...@gmail.com
> > > >> <mailto:
> > > >>>> mmyy1...@gmail.com>> <mmyy1...@gmail.com <mailto:
> mmyy1...@gmail.com
> > >>
> > > >> <
> > > >>>>>>
> > > >>>>>> mmyy1...@gmail.com <mailto:mmyy1...@gmail.com>>
> > > >>>>>>
> > > >>>>>> wrote:
> > > >>>>>>
> > > >>>>>> Hi Steven,
> > > >>>>>> Thank you for the feedback. Please take a look at the document
> > > >>>>>>
> > > >>>>>> FLIP-27
> > > >>>>>>
> > > >>>>>> <
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>
> > > >>>
> > > >>
> > >
> >
> https://cwiki.apache.org/confluence/display/FLINK/FLIP-27%3A+Refactor+Source+Interface
> > > >>>> <
> > > >>>>
> > > >>>
> > > >>
> > >
> >
> https://cwiki.apache.org/confluence/display/FLINK/FLIP-27%3A+Refactor+Source+Interface
> > > >>>>>
> > > >>>>>>
> > > >>>>>> which
> > > >>>>>>
> > > >>>>>> is updated recently. A lot of details of enumerator were added
> > > >>>>>>
> > > >>>>>> in
> > > >>>>>>
> > > >>>>>> this
> > > >>>>>>
> > > >>>>>> document. I think it would help.
> > > >>>>>>
> > > >>>>>> Steven Wu <stevenz...@gmail.com <mailto:stevenz...@gmail.com>>
> <
> > > >>>> stevenz...@gmail.com <mailto:stevenz...@gmail.com>> <
> > > >>> stevenz...@gmail.com
> > > >>>> <mailto:stevenz...@gmail.com>> <stevenz...@gmail.com <mailto:
> > > >>>> stevenz...@gmail.com>>
> > > >>>>>>
> > > >>>>>> 于2019年3月28日周四
> > > >>>>>>
> > > >>>>>> 下午12:52写道：
> > > >>>>>>
> > > >>>>>> This proposal mentioned that SplitEnumerator might run on the
> > > >>>>>> JobManager or
> > > >>>>>> in a single task on a TaskManager.
> > > >>>>>>
> > > >>>>>> if enumerator is a single task on a taskmanager, then the job
> > > >>>>>>
> > > >>>>>> DAG
> > > >>>>>>
> > > >>>>>> can
> > > >>>>>>
> > > >>>>>> never
> > > >>>>>> been embarrassingly parallel anymore. That will nullify the
> > > >>>>>>
> > > >>>>>> leverage
> > > >>>>>>
> > > >>>>>> of
> > > >>>>>>
> > > >>>>>> fine-grained recovery for embarrassingly parallel jobs.
> > > >>>>>>
> > > >>>>>> It's not clear to me what's the implication of running
> > > >>>>>>
> > > >>>>>> enumerator
> > > >>>>>>
> > > >>>>>> on
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> jobmanager. So I will leave that out for now.
> > > >>>>>>
> > > >>>>>> On Mon, Jan 28, 2019 at 3:05 AM Biao Liu <mmyy1...@gmail.com
> > > >> <mailto:
> > > >>>> mmyy1...@gmail.com>> <mmyy1...@gmail.com <mailto:
> mmyy1...@gmail.com
> > >>
> > > >> <
> > > >>>>>>
> > > >>>>>> mmyy1...@gmail.com <mailto:mmyy1...@gmail.com>>
> > > >>>>>>
> > > >>>>>> wrote:
> > > >>>>>>
> > > >>>>>> Hi Stephan & Piotrek,
> > > >>>>>>
> > > >>>>>> Thank you for feedback.
> > > >>>>>>
> > > >>>>>> It seems that there are a lot of things to do in community.
> > > >>>>>>
> > > >>>>>> I
> > > >>>>>>
> > > >>>>>> am
> > > >>>>>>
> > > >>>>>> just
> > > >>>>>>
> > > >>>>>> afraid that this discussion may be forgotten since there so
> > > >>>>>>
> > > >>>>>> many
> > > >>>>>>
> > > >>>>>> proposals
> > > >>>>>>
> > > >>>>>> recently.
> > > >>>>>> Anyway, wish to see the split topics soon :)
> > > >>>>>>
> > > >>>>>> Piotr Nowojski <pi...@da-platform.com <mailto:
> > pi...@da-platform.com
> > > >>>>
> > > >>> <
> > > >>>> pi...@da-platform.com <mailto:pi...@da-platform.com>> <
> > > >>>> pi...@da-platform.com <mailto:pi...@da-platform.com>> <
> > > >>>> pi...@da-platform.com <mailto:pi...@da-platform.com>>
> > > >>>>>>
> > > >>>>>> 于2019年1月24日周四
> > > >>>>>>
> > > >>>>>> 下午8:21写道：
> > > >>>>>>
> > > >>>>>> Hi Biao!
> > > >>>>>>
> > > >>>>>> This discussion was stalled because of preparations for
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> open
> > > >>>>>>
> > > >>>>>> sourcing
> > > >>>>>>
> > > >>>>>> & merging Blink. I think before creating the tickets we
> > > >>>>>>
> > > >>>>>> should
> > > >>>>>>
> > > >>>>>> split this
> > > >>>>>>
> > > >>>>>> discussion into topics/areas outlined by Stephan and
> > > >>>>>>
> > > >>>>>> create
> > > >>>>>>
> > > >>>>>> Flips
> > > >>>>>>
> > > >>>>>> for
> > > >>>>>>
> > > >>>>>> that.
> > > >>>>>>
> > > >>>>>> I think there is no chance for this to be completed in
> > > >>>>>>
> > > >>>>>> couple
> > > >>>>>>
> > > >>>>>> of
> > > >>>>>>
> > > >>>>>> remaining
> > > >>>>>>
> > > >>>>>> weeks/1 month before 1.8 feature freeze, however it would
> > > >>>>>>
> > > >>>>>> be
> > > >>>>>>
> > > >>>>>> good
> > > >>>>>>
> > > >>>>>> to aim
> > > >>>>>>
> > > >>>>>> with those changes for 1.9.
> > > >>>>>>
> > > >>>>>> Piotrek
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> On 20 Jan 2019, at 16:08, Biao Liu <mmyy1...@gmail.com <mailto:
> > > >>>> mmyy1...@gmail.com>> <mmyy1...@gmail.com <mailto:
> mmyy1...@gmail.com
> > >>
> > > >> <
> > > >>>>>>
> > > >>>>>> mmyy1...@gmail.com <mailto:mmyy1...@gmail.com>>
> > > >>>>>>
> > > >>>>>> wrote:
> > > >>>>>>
> > > >>>>>> Hi community,
> > > >>>>>> The summary of Stephan makes a lot sense to me. It is
> > > >>>>>>
> > > >>>>>> much
> > > >>>>>>
> > > >>>>>> clearer
> > > >>>>>>
> > > >>>>>> indeed
> > > >>>>>>
> > > >>>>>> after splitting the complex topic into small ones.
> > > >>>>>> I was wondering is there any detail plan for next step?
> > > >>>>>>
> > > >>>>>> If
> > > >>>>>>
> > > >>>>>> not,
> > > >>>>>>
> > > >>>>>> I
> > > >>>>>>
> > > >>>>>> would
> > > >>>>>>
> > > >>>>>> like to push this thing forward by creating some JIRA
> > > >>>>>>
> > > >>>>>> issues.
> > > >>>>>>
> > > >>>>>> Another question is that should version 1.8 include
> > > >>>>>>
> > > >>>>>> these
> > > >>>>>>
> > > >>>>>> features?
> > > >>>>>>
> > > >>>>>> Stephan Ewen <se...@apache.org <mailto:se...@apache.org>> <
> > > >>>> se...@apache.org <mailto:se...@apache.org>> <se...@apache.org
> > > <mailto:
> > > >>>> se...@apache.org>> <se...@apache.org <mailto:se...@apache.org>>
> > > >>>> 于2018年12月1日周六
> > > >>>>>>
> > > >>>>>> 上午4:20写道：
> > > >>>>>>
> > > >>>>>> Thanks everyone for the lively discussion. Let me try
> > > >>>>>>
> > > >>>>>> to
> > > >>>>>>
> > > >>>>>> summarize
> > > >>>>>>
> > > >>>>>> where I
> > > >>>>>>
> > > >>>>>> see convergence in the discussion and open issues.
> > > >>>>>> I'll try to group this by design aspect of the source.
> > > >>>>>>
> > > >>>>>> Please
> > > >>>>>>
> > > >>>>>> let me
> > > >>>>>>
> > > >>>>>> know
> > > >>>>>>
> > > >>>>>> if I got things wrong or missed something crucial here.
> > > >>>>>>
> > > >>>>>> For issues 1-3, if the below reflects the state of the
> > > >>>>>>
> > > >>>>>> discussion, I
> > > >>>>>>
> > > >>>>>> would
> > > >>>>>>
> > > >>>>>> try and update the FLIP in the next days.
> > > >>>>>> For the remaining ones we need more discussion.
> > > >>>>>>
> > > >>>>>> I would suggest to fork each of these aspects into a
> > > >>>>>>
> > > >>>>>> separate
> > > >>>>>>
> > > >>>>>> mail
> > > >>>>>>
> > > >>>>>> thread,
> > > >>>>>>
> > > >>>>>> or will loose sight of the individual aspects.
> > > >>>>>>
> > > >>>>>> *(1) Separation of Split Enumerator and Split Reader*
> > > >>>>>>
> > > >>>>>> - All seem to agree this is a good thing
> > > >>>>>> - Split Enumerator could in the end live on JobManager
> > > >>>>>>
> > > >>>>>> (and
> > > >>>>>>
> > > >>>>>> assign
> > > >>>>>>
> > > >>>>>> splits
> > > >>>>>>
> > > >>>>>> via RPC) or in a task (and assign splits via data
> > > >>>>>>
> > > >>>>>> streams)
> > > >>>>>>
> > > >>>>>> - this discussion is orthogonal and should come later,
> > > >>>>>>
> > > >>>>>> when
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> interface
> > > >>>>>>
> > > >>>>>> is agreed upon.
> > > >>>>>>
> > > >>>>>> *(2) Split Readers for one or more splits*
> > > >>>>>>
> > > >>>>>> - Discussion seems to agree that we need to support
> > > >>>>>>
> > > >>>>>> one
> > > >>>>>>
> > > >>>>>> reader
> > > >>>>>>
> > > >>>>>> that
> > > >>>>>>
> > > >>>>>> possibly handles multiple splits concurrently.
> > > >>>>>> - The requirement comes from sources where one
> > > >>>>>>
> > > >>>>>> poll()-style
> > > >>>>>>
> > > >>>>>> call
> > > >>>>>>
> > > >>>>>> fetches
> > > >>>>>>
> > > >>>>>> data from different splits / partitions
> > > >>>>>> --> example sources that require that would be for
> > > >>>>>>
> > > >>>>>> example
> > > >>>>>>
> > > >>>>>> Kafka,
> > > >>>>>>
> > > >>>>>> Pravega, Pulsar
> > > >>>>>>
> > > >>>>>> - Could have one split reader per source, or multiple
> > > >>>>>>
> > > >>>>>> split
> > > >>>>>>
> > > >>>>>> readers
> > > >>>>>>
> > > >>>>>> that
> > > >>>>>>
> > > >>>>>> share the "poll()" function
> > > >>>>>> - To not make it too complicated, we can start with
> > > >>>>>>
> > > >>>>>> thinking
> > > >>>>>>
> > > >>>>>> about
> > > >>>>>>
> > > >>>>>> one
> > > >>>>>>
> > > >>>>>> split reader for all splits initially and see if that
> > > >>>>>>
> > > >>>>>> covers
> > > >>>>>>
> > > >>>>>> all
> > > >>>>>>
> > > >>>>>> requirements
> > > >>>>>>
> > > >>>>>> *(3) Threading model of the Split Reader*
> > > >>>>>>
> > > >>>>>> - Most active part of the discussion ;-)
> > > >>>>>>
> > > >>>>>> - A non-blocking way for Flink's task code to interact
> > > >>>>>>
> > > >>>>>> with
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> source
> > > >>>>>>
> > > >>>>>> is
> > > >>>>>>
> > > >>>>>> needed in order to a task runtime code based on a
> > > >>>>>> single-threaded/actor-style task design
> > > >>>>>> --> I personally am a big proponent of that, it will
> > > >>>>>>
> > > >>>>>> help
> > > >>>>>>
> > > >>>>>> with
> > > >>>>>>
> > > >>>>>> well-behaved checkpoints, efficiency, and simpler yet
> > > >>>>>>
> > > >>>>>> more
> > > >>>>>>
> > > >>>>>> robust
> > > >>>>>>
> > > >>>>>> runtime
> > > >>>>>>
> > > >>>>>> code
> > > >>>>>>
> > > >>>>>> - Users care about simple abstraction, so as a
> > > >>>>>>
> > > >>>>>> subclass
> > > >>>>>>
> > > >>>>>> of
> > > >>>>>>
> > > >>>>>> SplitReader
> > > >>>>>>
> > > >>>>>> (non-blocking / async) we need to have a
> > > >>>>>>
> > > >>>>>> BlockingSplitReader
> > > >>>>>>
> > > >>>>>> which
> > > >>>>>>
> > > >>>>>> will
> > > >>>>>>
> > > >>>>>> form the basis of most source implementations.
> > > >>>>>>
> > > >>>>>> BlockingSplitReader
> > > >>>>>>
> > > >>>>>> lets
> > > >>>>>>
> > > >>>>>> users do blocking simple poll() calls.
> > > >>>>>> - The BlockingSplitReader would spawn a thread (or
> > > >>>>>>
> > > >>>>>> more)
> > > >>>>>>
> > > >>>>>> and
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> thread(s) can make blocking calls and hand over data
> > > >>>>>>
> > > >>>>>> buffers
> > > >>>>>>
> > > >>>>>> via
> > > >>>>>>
> > > >>>>>> a
> > > >>>>>>
> > > >>>>>> blocking
> > > >>>>>>
> > > >>>>>> queue
> > > >>>>>> - This should allow us to cover both, a fully async
> > > >>>>>>
> > > >>>>>> runtime,
> > > >>>>>>
> > > >>>>>> and a
> > > >>>>>>
> > > >>>>>> simple
> > > >>>>>>
> > > >>>>>> blocking interface for users.
> > > >>>>>> - This is actually very similar to how the Kafka
> > > >>>>>>
> > > >>>>>> connectors
> > > >>>>>>
> > > >>>>>> work.
> > > >>>>>>
> > > >>>>>> Kafka
> > > >>>>>>
> > > >>>>>> 9+ with one thread, Kafka 8 with multiple threads
> > > >>>>>>
> > > >>>>>> - On the base SplitReader (the async one), the
> > > >>>>>>
> > > >>>>>> non-blocking
> > > >>>>>>
> > > >>>>>> method
> > > >>>>>>
> > > >>>>>> that
> > > >>>>>>
> > > >>>>>> gets the next chunk of data would signal data
> > > >>>>>>
> > > >>>>>> availability
> > > >>>>>>
> > > >>>>>> via
> > > >>>>>>
> > > >>>>>> a
> > > >>>>>>
> > > >>>>>> CompletableFuture, because that gives the best
> > > >>>>>>
> > > >>>>>> flexibility
> > > >>>>>>
> > > >>>>>> (can
> > > >>>>>>
> > > >>>>>> await
> > > >>>>>>
> > > >>>>>> completion or register notification handlers).
> > > >>>>>> - The source task would register a "thenHandle()" (or
> > > >>>>>>
> > > >>>>>> similar)
> > > >>>>>>
> > > >>>>>> on the
> > > >>>>>>
> > > >>>>>> future to put a "take next data" task into the
> > > >>>>>>
> > > >>>>>> actor-style
> > > >>>>>>
> > > >>>>>> mailbox
> > > >>>>>>
> > > >>>>>> *(4) Split Enumeration and Assignment*
> > > >>>>>>
> > > >>>>>> - Splits may be generated lazily, both in cases where
> > > >>>>>>
> > > >>>>>> there
> > > >>>>>>
> > > >>>>>> is a
> > > >>>>>>
> > > >>>>>> limited
> > > >>>>>>
> > > >>>>>> number of splits (but very many), or splits are
> > > >>>>>>
> > > >>>>>> discovered
> > > >>>>>>
> > > >>>>>> over
> > > >>>>>>
> > > >>>>>> time
> > > >>>>>>
> > > >>>>>> - Assignment should also be lazy, to get better load
> > > >>>>>>
> > > >>>>>> balancing
> > > >>>>>>
> > > >>>>>> - Assignment needs support locality preferences
> > > >>>>>>
> > > >>>>>> - Possible design based on discussion so far:
> > > >>>>>>
> > > >>>>>> --> SplitReader has a method "addSplits(SplitT...)"
> > > >>>>>>
> > > >>>>>> to
> > > >>>>>>
> > > >>>>>> add
> > > >>>>>>
> > > >>>>>> one or
> > > >>>>>>
> > > >>>>>> more
> > > >>>>>>
> > > >>>>>> splits. Some split readers might assume they have only
> > > >>>>>>
> > > >>>>>> one
> > > >>>>>>
> > > >>>>>> split
> > > >>>>>>
> > > >>>>>> ever,
> > > >>>>>>
> > > >>>>>> concurrently, others assume multiple splits. (Note:
> > > >>>>>>
> > > >>>>>> idea
> > > >>>>>>
> > > >>>>>> behind
> > > >>>>>>
> > > >>>>>> being
> > > >>>>>>
> > > >>>>>> able
> > > >>>>>>
> > > >>>>>> to add multiple splits at the same time is to ease
> > > >>>>>>
> > > >>>>>> startup
> > > >>>>>>
> > > >>>>>> where
> > > >>>>>>
> > > >>>>>> multiple
> > > >>>>>>
> > > >>>>>> splits may be assigned instantly.)
> > > >>>>>> --> SplitReader has a context object on which it can
> > > >>>>>>
> > > >>>>>> call
> > > >>>>>>
> > > >>>>>> indicate
> > > >>>>>>
> > > >>>>>> when
> > > >>>>>>
> > > >>>>>> splits are completed. The enumerator gets that
> > > >>>>>>
> > > >>>>>> notification and
> > > >>>>>>
> > > >>>>>> can
> > > >>>>>>
> > > >>>>>> use
> > > >>>>>>
> > > >>>>>> to
> > > >>>>>>
> > > >>>>>> decide when to assign new splits. This should help both
> > > >>>>>>
> > > >>>>>> in
> > > >>>>>>
> > > >>>>>> cases
> > > >>>>>>
> > > >>>>>> of
> > > >>>>>>
> > > >>>>>> sources
> > > >>>>>>
> > > >>>>>> that take splits lazily (file readers) and in case the
> > > >>>>>>
> > > >>>>>> source
> > > >>>>>>
> > > >>>>>> needs to
> > > >>>>>>
> > > >>>>>> preserve a partial order between splits (Kinesis,
> > > >>>>>>
> > > >>>>>> Pravega,
> > > >>>>>>
> > > >>>>>> Pulsar may
> > > >>>>>>
> > > >>>>>> need
> > > >>>>>>
> > > >>>>>> that).
> > > >>>>>> --> SplitEnumerator gets notification when
> > > >>>>>>
> > > >>>>>> SplitReaders
> > > >>>>>>
> > > >>>>>> start
> > > >>>>>>
> > > >>>>>> and
> > > >>>>>>
> > > >>>>>> when
> > > >>>>>>
> > > >>>>>> they finish splits. They can decide at that moment to
> > > >>>>>>
> > > >>>>>> push
> > > >>>>>>
> > > >>>>>> more
> > > >>>>>>
> > > >>>>>> splits
> > > >>>>>>
> > > >>>>>> to
> > > >>>>>>
> > > >>>>>> that reader
> > > >>>>>> --> The SplitEnumerator should probably be aware of
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> source
> > > >>>>>>
> > > >>>>>> parallelism, to build its initial distribution.
> > > >>>>>>
> > > >>>>>> - Open question: Should the source expose something
> > > >>>>>>
> > > >>>>>> like
> > > >>>>>>
> > > >>>>>> "host
> > > >>>>>>
> > > >>>>>> preferences", so that yarn/mesos/k8s can take this into
> > > >>>>>>
> > > >>>>>> account
> > > >>>>>>
> > > >>>>>> when
> > > >>>>>>
> > > >>>>>> selecting a node to start a TM on?
> > > >>>>>>
> > > >>>>>> *(5) Watermarks and event time alignment*
> > > >>>>>>
> > > >>>>>> - Watermark generation, as well as idleness, needs to
> > > >>>>>>
> > > >>>>>> be
> > > >>>>>>
> > > >>>>>> per
> > > >>>>>>
> > > >>>>>> split
> > > >>>>>>
> > > >>>>>> (like
> > > >>>>>>
> > > >>>>>> currently in the Kafka Source, per partition)
> > > >>>>>> - It is desirable to support optional
> > > >>>>>>
> > > >>>>>> event-time-alignment,
> > > >>>>>>
> > > >>>>>> meaning
> > > >>>>>>
> > > >>>>>> that
> > > >>>>>>
> > > >>>>>> splits that are ahead are back-pressured or temporarily
> > > >>>>>>
> > > >>>>>> unsubscribed
> > > >>>>>>
> > > >>>>>> - I think i would be desirable to encapsulate
> > > >>>>>>
> > > >>>>>> watermark
> > > >>>>>>
> > > >>>>>> generation
> > > >>>>>>
> > > >>>>>> logic
> > > >>>>>>
> > > >>>>>> in watermark generators, for a separation of concerns.
> > > >>>>>>
> > > >>>>>> The
> > > >>>>>>
> > > >>>>>> watermark
> > > >>>>>>
> > > >>>>>> generators should run per split.
> > > >>>>>> - Using watermark generators would also help with
> > > >>>>>>
> > > >>>>>> another
> > > >>>>>>
> > > >>>>>> problem of
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> suggested interface, namely supporting non-periodic
> > > >>>>>>
> > > >>>>>> watermarks
> > > >>>>>>
> > > >>>>>> efficiently.
> > > >>>>>>
> > > >>>>>> - Need a way to "dispatch" next record to different
> > > >>>>>>
> > > >>>>>> watermark
> > > >>>>>>
> > > >>>>>> generators
> > > >>>>>>
> > > >>>>>> - Need a way to tell SplitReader to "suspend" a split
> > > >>>>>>
> > > >>>>>> until a
> > > >>>>>>
> > > >>>>>> certain
> > > >>>>>>
> > > >>>>>> watermark is reached (event time backpressure)
> > > >>>>>> - This would in fact be not needed (and thus simpler)
> > > >>>>>>
> > > >>>>>> if
> > > >>>>>>
> > > >>>>>> we
> > > >>>>>>
> > > >>>>>> had
> > > >>>>>>
> > > >>>>>> a
> > > >>>>>>
> > > >>>>>> SplitReader per split and may be a reason to re-open
> > > >>>>>>
> > > >>>>>> that
> > > >>>>>>
> > > >>>>>> discussion
> > > >>>>>>
> > > >>>>>> *(6) Watermarks across splits and in the Split
> > > >>>>>>
> > > >>>>>> Enumerator*
> > > >>>>>>
> > > >>>>>> - The split enumerator may need some watermark
> > > >>>>>>
> > > >>>>>> awareness,
> > > >>>>>>
> > > >>>>>> which
> > > >>>>>>
> > > >>>>>> should
> > > >>>>>>
> > > >>>>>> be
> > > >>>>>>
> > > >>>>>> purely based on split metadata (like create timestamp
> > > >>>>>>
> > > >>>>>> of
> > > >>>>>>
> > > >>>>>> file
> > > >>>>>>
> > > >>>>>> splits)
> > > >>>>>>
> > > >>>>>> - If there are still more splits with overlapping
> > > >>>>>>
> > > >>>>>> event
> > > >>>>>>
> > > >>>>>> time
> > > >>>>>>
> > > >>>>>> range
> > > >>>>>>
> > > >>>>>> for
> > > >>>>>>
> > > >>>>>> a
> > > >>>>>>
> > > >>>>>> split reader, then that split reader should not advance
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> watermark
> > > >>>>>>
> > > >>>>>> within the split beyond the overlap boundary. Otherwise
> > > >>>>>>
> > > >>>>>> future
> > > >>>>>>
> > > >>>>>> splits
> > > >>>>>>
> > > >>>>>> will
> > > >>>>>>
> > > >>>>>> produce late data.
> > > >>>>>>
> > > >>>>>> - One way to approach this could be that the split
> > > >>>>>>
> > > >>>>>> enumerator
> > > >>>>>>
> > > >>>>>> may
> > > >>>>>>
> > > >>>>>> send
> > > >>>>>>
> > > >>>>>> watermarks to the readers, and the readers cannot emit
> > > >>>>>>
> > > >>>>>> watermarks
> > > >>>>>>
> > > >>>>>> beyond
> > > >>>>>>
> > > >>>>>> that received watermark.
> > > >>>>>> - Many split enumerators would simply immediately send
> > > >>>>>>
> > > >>>>>> Long.MAX
> > > >>>>>>
> > > >>>>>> out
> > > >>>>>>
> > > >>>>>> and
> > > >>>>>>
> > > >>>>>> leave the progress purely to the split readers.
> > > >>>>>>
> > > >>>>>> - For event-time alignment / split back pressure, this
> > > >>>>>>
> > > >>>>>> begs
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> question
> > > >>>>>>
> > > >>>>>> how we can avoid deadlocks that may arise when splits
> > > >>>>>>
> > > >>>>>> are
> > > >>>>>>
> > > >>>>>> suspended
> > > >>>>>>
> > > >>>>>> for
> > > >>>>>>
> > > >>>>>> event time back pressure,
> > > >>>>>>
> > > >>>>>> *(7) Batch and streaming Unification*
> > > >>>>>>
> > > >>>>>> - Functionality wise, the above design should support
> > > >>>>>>
> > > >>>>>> both
> > > >>>>>>
> > > >>>>>> - Batch often (mostly) does not care about reading "in
> > > >>>>>>
> > > >>>>>> order"
> > > >>>>>>
> > > >>>>>> and
> > > >>>>>>
> > > >>>>>> generating watermarks
> > > >>>>>> --> Might use different enumerator logic that is
> > > >>>>>>
> > > >>>>>> more
> > > >>>>>>
> > > >>>>>> locality
> > > >>>>>>
> > > >>>>>> aware
> > > >>>>>>
> > > >>>>>> and ignores event time order
> > > >>>>>> --> Does not generate watermarks
> > > >>>>>> - Would be great if bounded sources could be
> > > >>>>>>
> > > >>>>>> identified
> > > >>>>>>
> > > >>>>>> at
> > > >>>>>>
> > > >>>>>> compile
> > > >>>>>>
> > > >>>>>> time,
> > > >>>>>>
> > > >>>>>> so that "env.addBoundedSource(...)" is type safe and
> > > >>>>>>
> > > >>>>>> can
> > > >>>>>>
> > > >>>>>> return a
> > > >>>>>>
> > > >>>>>> "BoundedDataStream".
> > > >>>>>> - Possible to defer this discussion until later
> > > >>>>>>
> > > >>>>>> *Miscellaneous Comments*
> > > >>>>>>
> > > >>>>>> - Should the source have a TypeInformation for the
> > > >>>>>>
> > > >>>>>> produced
> > > >>>>>>
> > > >>>>>> type,
> > > >>>>>>
> > > >>>>>> instead
> > > >>>>>>
> > > >>>>>> of a serializer? We need a type information in the
> > > >>>>>>
> > > >>>>>> stream
> > > >>>>>>
> > > >>>>>> anyways, and
> > > >>>>>>
> > > >>>>>> can
> > > >>>>>>
> > > >>>>>> derive the serializer from that. Plus, creating the
> > > >>>>>>
> > > >>>>>> serializer
> > > >>>>>>
> > > >>>>>> should
> > > >>>>>>
> > > >>>>>> respect the ExecutionConfig.
> > > >>>>>>
> > > >>>>>> - The TypeSerializer interface is very powerful but
> > > >>>>>>
> > > >>>>>> also
> > > >>>>>>
> > > >>>>>> not
> > > >>>>>>
> > > >>>>>> easy to
> > > >>>>>>
> > > >>>>>> implement. Its purpose is to handle data super
> > > >>>>>>
> > > >>>>>> efficiently,
> > > >>>>>>
> > > >>>>>> support
> > > >>>>>>
> > > >>>>>> flexible ways of evolution, etc.
> > > >>>>>> For metadata I would suggest to look at the
> > > >>>>>>
> > > >>>>>> SimpleVersionedSerializer
> > > >>>>>>
> > > >>>>>> instead, which is used for example for checkpoint
> > > >>>>>>
> > > >>>>>> master
> > > >>>>>>
> > > >>>>>> hooks,
> > > >>>>>>
> > > >>>>>> or for
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> streaming file sink. I think that is is a good match
> > > >>>>>>
> > > >>>>>> for
> > > >>>>>>
> > > >>>>>> cases
> > > >>>>>>
> > > >>>>>> where
> > > >>>>>>
> > > >>>>>> we
> > > >>>>>>
> > > >>>>>> do
> > > >>>>>>
> > > >>>>>> not need more than ser/deser (no copy, etc.) and don't
> > > >>>>>>
> > > >>>>>> need to
> > > >>>>>>
> > > >>>>>> push
> > > >>>>>>
> > > >>>>>> versioning out of the serialization paths for best
> > > >>>>>>
> > > >>>>>> performance
> > > >>>>>>
> > > >>>>>> (as in
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> TypeSerializer)
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> On Tue, Nov 27, 2018 at 11:45 AM Kostas Kloudas <
> > > >>>>>>
> > > >>>>>> k.klou...@data-artisans.com>
> > > >>>>>>
> > > >>>>>> wrote:
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> Hi Biao,
> > > >>>>>>
> > > >>>>>> Thanks for the answer!
> > > >>>>>>
> > > >>>>>> So given the multi-threaded readers, now we have as
> > > >>>>>>
> > > >>>>>> open
> > > >>>>>>
> > > >>>>>> questions:
> > > >>>>>>
> > > >>>>>> 1) How do we let the checkpoints pass through our
> > > >>>>>>
> > > >>>>>> multi-threaded
> > > >>>>>>
> > > >>>>>> reader
> > > >>>>>>
> > > >>>>>> operator?
> > > >>>>>>
> > > >>>>>> 2) Do we have separate reader and source operators or
> > > >>>>>>
> > > >>>>>> not? In
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> strategy
> > > >>>>>>
> > > >>>>>> that has a separate source, the source operator has a
> > > >>>>>>
> > > >>>>>> parallelism of
> > > >>>>>>
> > > >>>>>> 1
> > > >>>>>>
> > > >>>>>> and
> > > >>>>>>
> > > >>>>>> is responsible for split recovery only.
> > > >>>>>>
> > > >>>>>> For the first one, given also the constraints
> > > >>>>>>
> > > >>>>>> (blocking,
> > > >>>>>>
> > > >>>>>> finite
> > > >>>>>>
> > > >>>>>> queues,
> > > >>>>>>
> > > >>>>>> etc), I do not have an answer yet.
> > > >>>>>>
> > > >>>>>> For the 2nd, I think that we should go with separate
> > > >>>>>>
> > > >>>>>> operators
> > > >>>>>>
> > > >>>>>> for
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> source and the readers, for the following reasons:
> > > >>>>>>
> > > >>>>>> 1) This is more aligned with a potential future
> > > >>>>>>
> > > >>>>>> improvement
> > > >>>>>>
> > > >>>>>> where the
> > > >>>>>>
> > > >>>>>> split
> > > >>>>>>
> > > >>>>>> discovery becomes a responsibility of the JobManager
> > > >>>>>>
> > > >>>>>> and
> > > >>>>>>
> > > >>>>>> readers are
> > > >>>>>>
> > > >>>>>> pooling more work from the JM.
> > > >>>>>>
> > > >>>>>> 2) The source is going to be the "single point of
> > > >>>>>>
> > > >>>>>> truth".
> > > >>>>>>
> > > >>>>>> It
> > > >>>>>>
> > > >>>>>> will
> > > >>>>>>
> > > >>>>>> know
> > > >>>>>>
> > > >>>>>> what
> > > >>>>>>
> > > >>>>>> has been processed and what not. If the source and the
> > > >>>>>>
> > > >>>>>> readers
> > > >>>>>>
> > > >>>>>> are a
> > > >>>>>>
> > > >>>>>> single
> > > >>>>>>
> > > >>>>>> operator with parallelism > 1, or in general, if the
> > > >>>>>>
> > > >>>>>> split
> > > >>>>>>
> > > >>>>>> discovery
> > > >>>>>>
> > > >>>>>> is
> > > >>>>>>
> > > >>>>>> done by each task individually, then:
> > > >>>>>> i) we have to have a deterministic scheme for each
> > > >>>>>>
> > > >>>>>> reader to
> > > >>>>>>
> > > >>>>>> assign
> > > >>>>>>
> > > >>>>>> splits to itself (e.g. mod subtaskId). This is not
> > > >>>>>>
> > > >>>>>> necessarily
> > > >>>>>>
> > > >>>>>> trivial
> > > >>>>>>
> > > >>>>>> for
> > > >>>>>>
> > > >>>>>> all sources.
> > > >>>>>> ii) each reader would have to keep a copy of all its
> > > >>>>>>
> > > >>>>>> processed
> > > >>>>>>
> > > >>>>>> slpits
> > > >>>>>>
> > > >>>>>> iii) the state has to be a union state with a
> > > >>>>>>
> > > >>>>>> non-trivial
> > > >>>>>>
> > > >>>>>> merging
> > > >>>>>>
> > > >>>>>> logic
> > > >>>>>>
> > > >>>>>> in order to support rescaling.
> > > >>>>>>
> > > >>>>>> Two additional points that you raised above:
> > > >>>>>>
> > > >>>>>> i) The point that you raised that we need to keep all
> > > >>>>>>
> > > >>>>>> splits
> > > >>>>>>
> > > >>>>>> (processed
> > > >>>>>>
> > > >>>>>> and
> > > >>>>>>
> > > >>>>>> not-processed) I think is a bit of a strong
> > > >>>>>>
> > > >>>>>> requirement.
> > > >>>>>>
> > > >>>>>> This
> > > >>>>>>
> > > >>>>>> would
> > > >>>>>>
> > > >>>>>> imply
> > > >>>>>>
> > > >>>>>> that for infinite sources the state will grow
> > > >>>>>>
> > > >>>>>> indefinitely.
> > > >>>>>>
> > > >>>>>> This is
> > > >>>>>>
> > > >>>>>> problem
> > > >>>>>>
> > > >>>>>> is even more pronounced if we do not have a single
> > > >>>>>>
> > > >>>>>> source
> > > >>>>>>
> > > >>>>>> that
> > > >>>>>>
> > > >>>>>> assigns
> > > >>>>>>
> > > >>>>>> splits to readers, as each reader will have its own
> > > >>>>>>
> > > >>>>>> copy
> > > >>>>>>
> > > >>>>>> of
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> state.
> > > >>>>>>
> > > >>>>>> ii) it is true that for finite sources we need to
> > > >>>>>>
> > > >>>>>> somehow
> > > >>>>>>
> > > >>>>>> not
> > > >>>>>>
> > > >>>>>> close
> > > >>>>>>
> > > >>>>>> the
> > > >>>>>>
> > > >>>>>> readers when the source/split discoverer finishes. The
> > > >>>>>> ContinuousFileReaderOperator has a work-around for
> > > >>>>>>
> > > >>>>>> that.
> > > >>>>>>
> > > >>>>>> It is
> > > >>>>>>
> > > >>>>>> not
> > > >>>>>>
> > > >>>>>> elegant,
> > > >>>>>>
> > > >>>>>> and checkpoints are not emitted after closing the
> > > >>>>>>
> > > >>>>>> source,
> > > >>>>>>
> > > >>>>>> but
> > > >>>>>>
> > > >>>>>> this, I
> > > >>>>>>
> > > >>>>>> believe, is a bigger problem which requires more
> > > >>>>>>
> > > >>>>>> changes
> > > >>>>>>
> > > >>>>>> than
> > > >>>>>>
> > > >>>>>> just
> > > >>>>>>
> > > >>>>>> refactoring the source interface.
> > > >>>>>>
> > > >>>>>> Cheers,
> > > >>>>>> Kostas
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> --
> > > >>>>>> Best, Jingsong Lee
> > > >>>>
> > > >>>>
> > > >>>
> > > >>
> > > >>
> > > >> --
> > > >> Best, Jingsong Lee
> > > >>
> > > >
> > >
> > >
> >
>
