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From Fabian Hueske <fhue...@gmail.com>
Subject Re: How to contribute to Streaming Table API and StreamSQL
Date Thu, 13 Oct 2016 10:32:50 GMT
Hi Juho,

Yes, FLINK-4557 is an umbrella issue for windowed aggregations (both for
stream and batch) for the Table API (not including SQL).
The features are described in FLIP-11 [1]. Note, there is currently a
discussion about certain aspects of the proposed syntax [2].
There is a pull request for GroupWindow aggregates on streams (not batch)
[3] that should soon be good to merge (parts might be adapted depending on
the outcome of the discussion).
This feature should come with the next minor Flink release (1.2.0).

Support for GroupWindows in SQL depends on Apache Calcite. The Calcite
community is currently working on adding the required keywords to the
parser, validator and internal representation [4].

Let me know, if you have further questions.

Best, Fabian

[1]
https://cwiki.apache.org/confluence/display/FLINK/FLIP-11%3A+Table+API+Stream+Aggregations
[2]
http://apache-flink-mailing-list-archive.1008284.n3.nabble.com/RE-DISCUSS-FLIP-11-Table-API-Stream-Aggregations-tp13990.html
[3] https://github.com/apache/flink/pull/2562
[4] https://issues.apache.org/jira/browse/CALCITE-1345

2016-10-13 9:51 GMT+02:00 Juho Autio <juho.autio@rovio.com>:

> Hi Fabian!
>
> Is this the feature that will also add windowed aggregates to streaming
> SQL:
> https://issues.apache.org/jira/browse/FLINK-4557 (Table API Stream
> Aggregations)?
>
> You wrote:
>
> > However for the 1.2 release, it we plan to focus on the streaming
> > Table API and Stream SQL to add support for windowed aggregates and
> joins,
> > which corresponds to Task 7 and 9 in the design document.
>
> Is there any WIP implementation yet? I'd like to try it as soon as
> possible. Where can we track progress for Stream SQL windowed aggregates?
>
> (A little bit about our use case, if you're interested:
> In our company we enable stream aggregates declaratively on arbitrary JSON
> fields. User can choose an aggregate function, field to aggregate, group by
> fields, and filters. At the moment we use a custom ReduceFunction that
> accumulates the aggregates. Flink's upcoming Streaming SQL seems to answer
> our use case perfectly (especially the calcite sample query in
> https://flink.apache.org/news/2016/05/24/stream-sql.html). We would like
> to
> use that SQL instead of our custom reducer. Especially we want to switch to
> directly defining the user aggregates in that SQL syntax instead of the
> JSON configuration that we now have for the purpose.)
>
> Cheers,
> Juho
>
> On Fri, Jun 17, 2016 at 2:26 PM, Fabian Hueske <fhueske@gmail.com> wrote:
>
> > If we want to have it in Stream SQL yes. Although we can also think about
> > extending the Calcite parser ourselves.
> > IMO, it makes sense to talk to them first, also to get more feedback on
> the
> > feature.
> >
> >
> > 2016-06-17 13:18 GMT+02:00 Jark Wu <wuchong.wc@alibaba-inc.com>:
> >
> > > Hi Fabian,
> > >
> > > Yea, we can immediately start to work on non-windowed aggregates. But
> it
> > > seems that Calcite’s StreamSQL doesn’t support non-windowed aggregates
> > > (also not included in roadmap). So we may need to propose this function
> > > back to Calcite community?
> > >
> > > - Jark Wu
> > >
> > > > 在 2016年6月17日,下午5:41,Fabian Hueske <fhueske@gmail.com>
写道:
> > > >
> > > > Hi Jark Wu,
> > > >
> > > > I agree about the non-windowed aggregates. If there are actual use
> > cases
> > > > for this operator, we should definitely support it.
> > > > Since it does not depend on windows or time, we can immediately start
> > to
> > > > work on it. In principle, it should be rather easy to implement.
> > > > However, we have to check how well it integrates with the current
> state
> > > of
> > > > Calcite.
> > > >
> > > > I think forking off a feature branch is a good idea. We have done
> that
> > > > before (e.g., for porting the Table API on top of Calcite), but it is
> > not
> > > > so common in the Flink community.
> > > > So I would first send a note to the dev list and check that nobody
> > > objects.
> > > >
> > > > I think we can decouple the development of the Table API and SQL.
> > > Although
> > > > it is desirable to have the same feature set in both APIs, I would
> not
> > be
> > > > strict about it.
> > > > However, the Table API does also depend on Calcite because all Table
> > API
> > > > queries go through Calcite's logical plan representation and
> optimizer.
> > > By
> > > > decoupling the SQL and Table API feature development, we do not need
> to
> > > > wait for the SQL parser but still might still need certain features
> in
> > > the
> > > > logical plan or optimizer. I hope we can solve a lot with custom
> > RelNodes
> > > > and optimizer rules which should eventually be contributed back to
> > > Calcite.
> > > >
> > > > Best, Fabian
> > > >
> > > >
> > > > 2016-06-17 9:48 GMT+02:00 Jark Wu <wuchong.wc@alibaba-inc.com>:
> > > >
> > > >> Hi Fabian,
> > > >>
> > > >> There are a lot of our business are using non-windowed aggregations.
> > And
> > > >> there is a little difference between non-windowed aggregate and Row
> > > window
> > > >> operator, as the later is bound to a certain window and emit the
> > result
> > > of
> > > >> the N rows preceding for every incoming row. However the former emit
> > the
> > > >> aggregate result of the whole elements. So I suggest to add them for
> > > more
> > > >> complete semantic.
> > > >>
> > > >> Regarding the windowed aggregate task, I’m agree with that and I'm
> > > looking
> > > >> forward as soon as possible to see the corresponding JIRA issues
> > > created.
> > > >> After that, we can start working on an independent branch without
> > > waiting
> > > >> for 1.1 released. But I’m still a little concerned about Calcite’s
> > > support,
> > > >> as we must waiting for Calcite supporting correspond syntax and the
> > > >> version released. If we can separate the task into Table API and SQL
> > ,
> > > we
> > > >> may not be blocked by Calcite too much.
> > > >>
> > > >> What do you think?
> > > >>
> > > >> - Jark Wu
> > > >>
> > > >>> 在 2016年6月16日,下午8:37,Fabian Hueske <fhueske@gmail.com>
写道:
> > > >>>
> > > >>> Hi Jark,
> > > >>>
> > > >>> thanks for sharing Blink's Streaming Table API. It seems to be
> close
> > to
> > > >> the
> > > >>> DataStream API, while the Table API draft I shared is more similar
> to
> > > >>> Calcite's proposal.
> > > >>> You are right, the current draft does not include running
> > > (non-windowed)
> > > >>> aggregates. We were not sure how useful these are since these
> > > aggregates
> > > >>> are unbound and might become meaningless after being applied on
a
> > very
> > > >> long
> > > >>> stream. However, we can certainly add them, if users request them.
> > > >>> An alternative to running aggregates could be what I called "Row
> > window
> > > >>> operators" in the streaming Table API draft. These operators emit
> an
> > > >>> aggregate for each incoming row, however the aggregate is bound
to
> a
> > > >>> certain window around the row like the 10 rows preceding the row
> for
> > > >> which
> > > >>> the aggregate is computed. Calcite calls these windows "Sliding
> > > windows"
> > > >>> (Attention: This is different from Flink's terminology, in Flink
> > > sliding
> > > >>> windows are something different). Row windows are similar to
> running
> > > >>> aggregates in that they emit a row for each incoming row. You
can
> > also
> > > >>> think of them as a (Flink) sliding count window which is evaluate
> for
> > > >> each
> > > >>> incoming record.
> > > >>>
> > > >>> Further differences are the support of Scalar UDFs in the Table
API
> > and
> > > >> the
> > > >>> support for joins which have not been drafted for the Table API
> yet.
> > > >>> Scalar UDFs are definitely also on our roadmap and with upcoming
> > > support
> > > >>> for side inputs, the DataStream API will also support more types
of
> > > >> joins.
> > > >>>
> > > >>> Regarding the current state of Stream SQL in Calcite I am not
up to
> > > date.
> > > >>>
> > > >>> I would propose to start with the effort of adding support for
> > windowed
> > > >>> aggregates as follows:
> > > >>>
> > > >>> 1) Add support to define a timestamp / watermark extractor to
> tables.
> > > >> This
> > > >>> includes to define a "quasi-monotone" column in a Table's schema.
> > > Calcite
> > > >>> will use this information to reason about the validity of a query
> > > (making
> > > >>> sure that grouping includes at least one monotone attribute).
> > > >>> 2) Add support for sorting a stream on the timestamp attribute.
> While
> > > >>> sorting itself is not very exciting, it is an easy operation and
> can
> > be
> > > >>> immediately implemented without worrying about API questions.
This
> > will
> > > >>> also show how well Calcite supports the reasoning about monotone
> > > >> attributes.
> > > >>> 3) Add support for tumbling windows.
> > > >>>
> > > >>> In each of these steps we might need to get involved with the
> Calcite
> > > >>> community, depending on Calcite's current support for
> > "quasi-monotone"
> > > >>> attributes, etc.
> > > >>>
> > > >>> What do you think?
> > > >>>
> > > >>> Best, Fabian
> > > >>>
> > > >>>
> > > >>> 2016-06-14 11:03 GMT+02:00 Jark Wu <wuchong.wc@alibaba-inc.com>:
> > > >>>
> > > >>>> Hi Fabian,
> > > >>>>
> > > >>>> It’s great to hear that we are going to start it!
> > > >>>>
> > > >>>> I’m glad to share our current Streaming Table API [1]. I
find that
> > > that
> > > >>>> all aggregation functions are scoped to the defined window
in
> Flink
> > > >> Stream
> > > >>>> Table API design [2] and Calcite StreamSQL desgin [3]. I’m
> thinking
> > > >> that do
> > > >>>> we need global aggregation? The global aggregation means that
> > > >> aggregation
> > > >>>> is applied only on grouped key not including window which
is
> > supported
> > > >> in
> > > >>>> DataStream `datastream.keyBy(f1).sum(f2)`.
> > > >>>>
> > > >>>> Since the window syntax of StreamSQL is not implemented yet,
so
> will
> > > we
> > > >>>> help Calcite community with that first or work code for window+agg
> > > Table
> > > >>>> API first ?
> > > >>>>
> > > >>>>
> > > >>>> [1]
> > > >>>>
> > > >>
> > > https://docs.google.com/document/d/1KMUzvBAWSyQ39T8MyxUi0zNH
> > yvLUnyGMPA7_RLSDpFw/edit?usp=sharing
> > > >>>> <
> > > >>>>
> > > >>
> > > https://docs.google.com/document/d/1KMUzvBAWSyQ39T8MyxUi0zNH
> > yvLUnyGMPA7_RLSDpFw/edit?usp=sharing
> > > >>>>>
> > > >>>> [2]
> > > >>>>
> > > >>
> > > https://docs.google.com/document/d/19kSOAOINKCSWLBCKRq2WvNtm
> > uaA9o3AyCh2ePqr3V5E/edit#
> > > >>>> <
> > > >>>>
> > > >>
> > > https://docs.google.com/document/d/19kSOAOINKCSWLBCKRq2WvNtm
> > uaA9o3AyCh2ePqr3V5E/edit#
> > > >>>>>
> > > >>>> [3] https://calcite.apache.org/docs/stream.html#tumbling-windows
> <
> > > >>>> https://calcite.apache.org/docs/stream.html#tumbling-windows>
> > > >>>>
> > > >>>>
> > > >>>> - Jark Wu
> > > >>>>
> > > >>>>> 在 2016年6月14日,上午1:10,Fabian Hueske <fhueske@gmail.com>
写道:
> > > >>>>>
> > > >>>>> Hi Jark,
> > > >>>>>
> > > >>>>> wow, that's good news!
> > > >>>>> You are right, the streaming Table API is currently very
limited.
> > In
> > > >> the
> > > >>>>> last month's we changed the internal architecture and
put
> > everything
> > > on
> > > >>>> top
> > > >>>>> of Apache Calcite.
> > > >>>>> For the upcoming 1.1 release, we won't add new features
to the
> > Table
> > > >> API
> > > >>>> /
> > > >>>>> SQL. However for the 1.2 release, it we plan to focus
on the
> > > streaming
> > > >>>>> Table API and Stream SQL to add support for windowed aggregates
> and
> > > >>>> joins,
> > > >>>>> which corresponds to Task 7 and 9 in the design document.
You are
> > > >>>>> completely right, that we should start to add tickets
to JIRA for
> > > >> this. I
> > > >>>>> will do that tomorrow.
> > > >>>>>
> > > >>>>> It is great that you have already working code for windowed
> > > aggregates
> > > >>>> and
> > > >>>>> joins! Here is a link to our current API draft for windows
in the
> > > Table
> > > >>>> API
> > > >>>>> [1]. Would be great if you could share how your API looks
like.
> As
> > > you
> > > >>>>> said, the internals have changed a lot by now, but we
might want
> to
> > > >> reuse
> > > >>>>> your API for Table API windows and maybe the code of the
runtime.
> > > >>>> However,
> > > >>>>> we need to go through Calcite for optimization and SQL
support,
> so
> > > some
> > > >>>>> parts need to be definitely changed. Stream SQL is also
on the
> > > roadmap
> > > >> of
> > > >>>>> the Calcite community, but it might be that some features
that we
> > > will
> > > >>>> need
> > > >>>>> are not completed yet. So, maybe we help the Calcite community
> with
> > > >> that
> > > >>>> as
> > > >>>>> well.
> > > >>>>>
> > > >>>>> If you want to contribute, you should first read the how
to
> > > contribute
> > > >>>>> guide [2] and guide for code contributions [3].
> > > >>>>> The general rule is to first open a JIRA and later a pull
> request.
> > > >>>> Changes
> > > >>>>> that are extensive or modify current behavior (except
bugs)
> should
> > be
> > > >>>>> discussed before starting to work on them.
> > > >>>>>
> > > >>>>> Looking forward to work with you on Flink,
> > > >>>>> Fabian
> > > >>>>>
> > > >>>>> [1]
> > > >>>>>
> > > >>>>
> > > >>
> > > https://docs.google.com/document/d/19kSOAOINKCSWLBCKRq2WvNtm
> > uaA9o3AyCh2ePqr3V5E/edit#heading=h.3iw7frfjdcb2
> > > >>>>> [2] http://flink.apache.org/how-to-contribute.html
> > > >>>>> [3] http://flink.apache.org/contribute-code.html
> > > >>>>>
> > > >>>>>
> > > >>>>> 2016-06-13 11:31 GMT+02:00 Jark Wu <wuchong.wc@alibaba-inc.com>:
> > > >>>>>
> > > >>>>>> Hi,
> > > >>>>>>
> > > >>>>>> We have a great interest in the new Table API &
SQL. In Alibaba,
> > we
> > > >> have
> > > >>>>>> added a lot of features (groupBy, agg, window, join,
UDF …) to
> > > >> Streaming
> > > >>>>>> Table API (base on Flink 1.0). Now, many jobs run
on Table API
> in
> > > >>>>>> production environment. But we want to keep pace with
the
> > community,
> > > >>>> and we
> > > >>>>>> have noticed that Flink Community reworked the Table
API and
> also
> > > >>>> supported
> > > >>>>>> SQL. That is really cool. However, the Streaming Table
API is
> > still
> > > so
> > > >>>>>> weak. So we want to contribute to accelerate the Streaming
Table
> > API
> > > >> and
> > > >>>>>> StreamSQL growth.
> > > >>>>>>
> > > >>>>>> It seems that we have complete Task-5 and Task-6 mentioned
in
> the
> > > Work
> > > >>>>>> Plan <
> > > >>>>>>
> > > >>>>
> > > >>
> > > https://docs.google.com/document/d/1TLayJNOTBle_-m1rQfgA6Ouj
> > 1oYsfqRjPcp1h2TVqdI/edit#
> > > >>>>> .
> > > >>>>>> So can we start Task-7 and Task-9 now? Is there any
more
> specific
> > > >>>> plans? I
> > > >>>>>> think it’s better to create an umbrella JIRA like
FLINK-3221 to
> > make
> > > >> the
> > > >>>>>> develop plan clearer.
> > > >>>>>>
> > > >>>>>> If I want to contribute code for groupBy and agg function,
what
> > > >> should I
> > > >>>>>> do? As I didn’t find related JIRAs, can I create
JIRA and pull a
> > > >> request
> > > >>>>>> directly?
> > > >>>>>>
> > > >>>>>> Sorry for so many questions at a time.
> > > >>>>>>
> > > >>>>>>
> > > >>>>>>
> > > >>>>>> - Jark Wu (wuchong)
> > > >>>>>>
> > > >>>>>>
> > > >>>>
> > > >>>>
> > > >>
> > > >>
> > >
> > >
> >
>

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