I agree, the groupBy, in the batch API is misleading, since a ds.groupBy().reduce() does not really build any groups, it is really a ds.keyBy().reduceByKey(). In the streaming API we can still fix this, IMHO.
On Tue, 14 Jul 2015 at 10:56 Stephan Ewen <se...@apache.org> wrote: > It is not a bit different than the batch API, because streaming semantics > are a bit different ;-) > > One good thing is that we can make things better that were sub-optimal in > the Batch API. > > On Tue, Jul 14, 2015 at 10:55 AM, Stephan Ewen <se...@apache.org> wrote: > > > keyBy() does not do any grouping. Grouping in streams in not defined > > without windows. > > > > On Tue, Jul 14, 2015 at 10:48 AM, Gyula Fóra <gyula.f...@gmail.com> > wrote: > > > >> If we only want to have either keyBy or groupBy, why not keep groupBy? > >> That > >> would be more consistent with the batch api. > >> On Tue, Jul 14, 2015 at 10:35 AM Stephan Ewen <se...@apache.org> wrote: > >> > >> > Concerning your comments: > >> > > >> > 1) In the new design, there is no grouping without windowing. The > >> > KeyedDataStream subsumes the grouping and key-ing for partitioned > state. > >> > > >> > The keyBy() + window() makes a parallel grouped window > >> > keyBy() alone allows access to partitioned state. > >> > > >> > My thought was that this is simpler, because it needs not > groupBy() > >> and > >> > keyBy(), but one construct to handle both cases. > >> > > >> > 2) The discretization is a rough thought and is nothing for the short > >> term. > >> > It totally needs more thoughts. I put it there to have it as a sketch > >> for > >> > how to evolve this. > >> > > >> > The idea is of course to not have a single data set, but a series > of > >> > data set. In each discrete time slice, the data set can be treated > like > >> a > >> > regular data set. > >> > > >> > Let's kick off a separate design for the discretization. Joins are > >> good > >> > to talk about (data sets can be joined with data set), and I am sure > >> there > >> > are more questions coming up. > >> > > >> > > >> > Does that make sense? > >> > > >> > > >> > > >> > > >> > > >> > On Tue, Jul 14, 2015 at 10:05 AM, Gyula Fóra <gyula.f...@gmail.com> > >> wrote: > >> > > >> > > I think Marton has some good points here. > >> > > > >> > > 1) Is KeyedDataStream a better name if this is only a renaming? > >> > > > >> > > 2) the discretize semantics is unclear indeed. Are we operating on a > >> > single > >> > > or sequence of datasets? If the latter why not call it something > else > >> > > (dstream). How are joins and other binary operators defined for > >> different > >> > > discretizations etc. > >> > > On Mon, Jul 13, 2015 at 7:37 PM Márton Balassi <mbala...@apache.org > > > >> > > wrote: > >> > > > >> > > > Generally I agree with the new design. Two concerns: > >> > > > > >> > > > 1) Does KeyedDataStream replace GroupedDataStream or is it the > >> latter a > >> > > > special case of the former? > >> > > > > >> > > > The KeyedDataStream as described in the design document is a bit > >> > unclear > >> > > > for me. It lists the following usages: > >> > > > a) It is the first step in building a window stream, on top of > >> which > >> > > the > >> > > > grouped/windowed aggregation and reduce-style function can be > >> applied > >> > > > b) It allows to use the "by-key" state of functions. Here, every > >> > record > >> > > > has access to a state that is scoped by its key. Key-scoped state > >> can > >> > be > >> > > > automatically redistributed and repartitioned. > >> > > > > >> > > > The code snippet describes a use case where the computation and > the > >> > > access > >> > > > of the state is used the way currently the GroupedDataStream > should > >> > > work. I > >> > > > suppose this is the example for case b). Would case a) also window > >> > > elements > >> > > > by key? If yes, then this is practically a renaming and > enhancement > >> of > >> > > the > >> > > > GroupedDataStream functionality with keyed state. Then the > >> > > > StreamExecutionEnvironment.createKeyedStream(Partitioner, > >> > > > KeySelector)construction does not make much sense as the user only > >> > > operates > >> > > > within the scope of the keyselector and not the partitioner > anyway. > >> > > > > >> > > > I personally think KeyedDataStream as a name does not necessarily > >> > suggest > >> > > > that the records are grouped by key, it only suggests partitioning > >> by > >> > > key - > >> > > > at least for me. :) > >> > > > > >> > > > 2) The API for discretization is not convenient IMHO > >> > > > > >> > > > The discretization part declares that the output of > >> > > DataStream.discretize() > >> > > > is a sequence of DataSets. I love this approach, but then in the > >> code > >> > > > snippet the return value of this function is simply a DataSet and > >> uses > >> > it > >> > > > as such. The take home message of that code is the following: this > >> is > >> > > > actually the way you would like to program on these sequence of > >> > DataSets, > >> > > > most probably you would like to do the same with each of them. If > >> that > >> > is > >> > > > the case we should provide a nice utility for that. I think Spark > >> > > > Streaming's DStream.foreachRDD() is fairly useful for this > purpose. > >> > > > > >> > > > On Mon, Jul 13, 2015 at 6:30 PM, Gyula Fóra <gyula.f...@gmail.com > > > >> > > wrote: > >> > > > > >> > > > > +1 > >> > > > > On Mon, Jul 13, 2015 at 6:23 PM Stephan Ewen <se...@apache.org> > >> > wrote: > >> > > > > > >> > > > > > If naming is the only concern, then we should go ahead, > because > >> we > >> > > can > >> > > > > > change names easily (before the release). > >> > > > > > > >> > > > > > In fact, I don't think it leaves a bad impression. Global > >> windows > >> > are > >> > > > > > non-parallel windows. There are also parallel windows. Pick > what > >> > you > >> > > > need > >> > > > > > and what works. > >> > > > > > > >> > > > > > > >> > > > > > On Mon, Jul 13, 2015 at 6:13 PM, Gyula Fóra < > >> gyula.f...@gmail.com> > >> > > > > wrote: > >> > > > > > > >> > > > > > > I think we agree on everything its more of a naming issue :) > >> > > > > > > > >> > > > > > > I thought it might be misleading that global time windows > are > >> > > > > > > "non-parallel" windows. We dont want to give a bad > impression. > >> > > (Also > >> > > > we > >> > > > > > > dont want them to think that every global window is parallel > >> but > >> > > > thats > >> > > > > > not > >> > > > > > > a problem here) > >> > > > > > > > >> > > > > > > Gyula > >> > > > > > > On Mon, Jul 13, 2015 at 5:22 PM Stephan Ewen < > >> se...@apache.org> > >> > > > wrote: > >> > > > > > > > >> > > > > > > > Okay, what is missing about the windowing in your opinion? > >> > > > > > > > > >> > > > > > > > The core points of the document are: > >> > > > > > > > > >> > > > > > > > - The parallel windows are per group only. > >> > > > > > > > > >> > > > > > > > - The implementation of the parallel windows holds > window > >> > data > >> > > in > >> > > > > the > >> > > > > > > > group buffers. > >> > > > > > > > > >> > > > > > > > - The global windows are non-parallel. May have parallel > >> > > > > > > pre-aggregation, > >> > > > > > > > if they are time windows. > >> > > > > > > > > >> > > > > > > > - Time may be operator time (timer thread), or watermark > >> > time. > >> > > > > > > Watermark > >> > > > > > > > time can refer to ingress or event time. > >> > > > > > > > > >> > > > > > > > - Windows that do not pre-aggregate may require elements > >> in > >> > > > order. > >> > > > > > Not > >> > > > > > > > part of the first prototype. > >> > > > > > > > > >> > > > > > > > Do we agree on those points? > >> > > > > > > > > >> > > > > > > > > >> > > > > > > > On Mon, Jul 13, 2015 at 4:50 PM, Gyula Fóra < > >> > > gyula.f...@gmail.com> > >> > > > > > > wrote: > >> > > > > > > > > >> > > > > > > > > In general I like it, although the main difference > between > >> > the > >> > > > > > current > >> > > > > > > > and > >> > > > > > > > > the new one is the windowing and that is still not very > >> > clear. > >> > > > > > > > > > >> > > > > > > > > Where do we have the full stream time windows for > >> > > instance?(which > >> > > > > is > >> > > > > > > > > parallel but not keyed) > >> > > > > > > > > On Mon, Jul 13, 2015 at 4:28 PM Aljoscha Krettek < > >> > > > > > aljos...@apache.org> > >> > > > > > > > > wrote: > >> > > > > > > > > > >> > > > > > > > > > +1 I like it as well. > >> > > > > > > > > > > >> > > > > > > > > > On Mon, 13 Jul 2015 at 16:17 Kostas Tzoumas < > >> > > > ktzou...@apache.org > >> > > > > > > >> > > > > > > > wrote: > >> > > > > > > > > > > >> > > > > > > > > > > +1 from my side > >> > > > > > > > > > > > >> > > > > > > > > > > On Mon, Jul 13, 2015 at 4:15 PM, Stephan Ewen < > >> > > > > se...@apache.org> > >> > > > > > > > > wrote: > >> > > > > > > > > > > > >> > > > > > > > > > > > Do we have consensus on these designs? > >> > > > > > > > > > > > > >> > > > > > > > > > > > If we have, we should get to implementing this > soon, > >> > > > because > >> > > > > > > > > basically > >> > > > > > > > > > > all > >> > > > > > > > > > > > streaming patches will have to be revisited in > >> light of > >> > > > > this... > >> > > > > > > > > > > > > >> > > > > > > > > > > > On Tue, Jul 7, 2015 at 3:41 PM, Gyula Fóra < > >> > > > > > gyula.f...@gmail.com > >> > > > > > > > > >> > > > > > > > > > wrote: > >> > > > > > > > > > > > > >> > > > > > > > > > > > > You are right thats an important issue. > >> > > > > > > > > > > > > > >> > > > > > > > > > > > > And I think we should also do some renaming with > >> the > >> > > > > > > "iterations" > >> > > > > > > > > > > because > >> > > > > > > > > > > > > they are not really iterations like in the batch > >> case > >> > > and > >> > > > > it > >> > > > > > > > might > >> > > > > > > > > > > > confuse > >> > > > > > > > > > > > > some users. > >> > > > > > > > > > > > > Maybe we can call them loops or cycles and > rename > >> the > >> > > api > >> > > > > > calls > >> > > > > > > > to > >> > > > > > > > > > make > >> > > > > > > > > > > > it > >> > > > > > > > > > > > > more intuitive what happens. It is really just a > >> > cyclic > >> > > > > > > dataflow. > >> > > > > > > > > > > > > > >> > > > > > > > > > > > > Aljoscha Krettek <aljos...@apache.org> ezt írta > >> > > > (időpont: > >> > > > > > > 2015. > >> > > > > > > > > júl. > >> > > > > > > > > > > 7., > >> > > > > > > > > > > > > K, > >> > > > > > > > > > > > > 15:35): > >> > > > > > > > > > > > > > >> > > > > > > > > > > > > > Hi, > >> > > > > > > > > > > > > > I just noticed that we don't have anything > about > >> > how > >> > > > > > > iterations > >> > > > > > > > > and > >> > > > > > > > > > > > > > timestamps/watermarks should interact. > >> > > > > > > > > > > > > > > >> > > > > > > > > > > > > > Cheers, > >> > > > > > > > > > > > > > Aljoscha > >> > > > > > > > > > > > > > > >> > > > > > > > > > > > > > On Mon, 6 Jul 2015 at 23:56 Stephan Ewen < > >> > > > > se...@apache.org > >> > > > > > > > >> > > > > > > > > wrote: > >> > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > Hi all! > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > As many of you know, there are a ongoing > >> efforts > >> > to > >> > > > > > > > consolidate > >> > > > > > > > > > the > >> > > > > > > > > > > > > > > streaming API for the next release, and then > >> > > graduate > >> > > > > it > >> > > > > > > > (from > >> > > > > > > > > > beta > >> > > > > > > > > > > > > > > status). > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > In the process of this consolidation, we > want > >> to > >> > > > > achieve > >> > > > > > > the > >> > > > > > > > > > > > following > >> > > > > > > > > > > > > > > goals. > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > - Make the code more robust and simplify it > >> in > >> > > parts > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > - Clearly define the semantics of the > >> > constructs. > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > - Prepare it for support of more advanced > >> > > concepts, > >> > > > > like > >> > > > > > > > > > > > partitionable > >> > > > > > > > > > > > > > > state, and event time. > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > - Cut support for certain corner cases that > >> were > >> > > > > > > prototyped, > >> > > > > > > > > but > >> > > > > > > > > > > > > turned > >> > > > > > > > > > > > > > > out to be not efficiently doable > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > Based on prior discussions on the mailing > >> list, > >> > > > > Aljoscha > >> > > > > > > and > >> > > > > > > > me > >> > > > > > > > > > > > drafted > >> > > > > > > > > > > > > > the > >> > > > > > > > > > > > > > > design documents below, which outline how > the > >> > > > > > consolidated > >> > > > > > > > API > >> > > > > > > > > > > would > >> > > > > > > > > > > > > > like. > >> > > > > > > > > > > > > > > We focused in constructs, time, and window > >> > > semantics. > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > Design document on how to restructure the > >> > Streaming > >> > > > > API: > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > > > > > > >> > > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > https://cwiki.apache.org/confluence/display/FLINK/Streams+and+Operations+on+Streams > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > Design document on definitions of time, > order, > >> > and > >> > > > the > >> > > > > > > > > resulting > >> > > > > > > > > > > > > > semantics: > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > > > > > > >> > > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > https://cwiki.apache.org/confluence/display/FLINK/Time+and+Order+in+Streams > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > Note: The design of the interfaces and > >> concepts > >> > for > >> > > > > > > advanced > >> > > > > > > > > > state > >> > > > > > > > > > > in > >> > > > > > > > > > > > > > > functions is not in here. That is part of a > >> > > separate > >> > > > > > design > >> > > > > > > > > > > > discussion > >> > > > > > > > > > > > > > and > >> > > > > > > > > > > > > > > orthogonal to the designs drafted here. > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > Please have a look and voice questions and > >> > > concerns. > >> > > > > > Since > >> > > > > > > we > >> > > > > > > > > > > should > >> > > > > > > > > > > > > not > >> > > > > > > > > > > > > > > break the streaming API more than once, we > >> should > >> > > > make > >> > > > > > sure > >> > > > > > > > > this > >> > > > > > > > > > > > > > > consolidation brings it into the shape we > >> want it > >> > > to > >> > > > be > >> > > > > > in. > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > Greetings, > >> > > > > > > > > > > > > > > Stephan > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > > > > > > >> > > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > > > > >
