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Re: [DISCUSS] Support Interactive Programming in Flink Table API


Hi,

Thanks for the proposal!

To summarize, you propose a new method Table.cache(): Table that will
trigger a job and write the result into some temporary storage as defined
by a TableFactory.
The cache() call blocks while the job is running and eventually returns a
Table object that represents a scan of the temporary table.
When the "session" is closed (closing to be defined?), the temporary tables
are all dropped.

I think this behavior makes sense and is a good first step towards more
interactive workloads.
However, its performance suffers from writing to and reading from external
systems.
I think this is OK for now. Changes that would significantly improve the
situation (i.e., pinning data in-memory across jobs) would have large
impacts on many components of Flink.
Users could use in-memory filesystems or storage grids (Apache Ignite) to
mitigate some of the performance effects.

Best, Fabian



Am Mo., 26. Nov. 2018 um 03:38 Uhr schrieb Becket Qin <becket.qin@xxxxxxxxx
>:

> Thanks for the explanation, Piotrek.
>
> Is there any extra thing user can do on a MaterializedTable that they
> cannot do on a Table? After users call *table.cache(), *users can just use
> that table and do anything that is supported on a Table, including SQL.
>
> Naming wise, either cache() or materialize() sounds fine to me. cache() is
> a bit more general than materialize(). Given that we are enhancing the
> Table API to also support non-relational processing cases, cache() might be
> slightly better.
>
> Thanks,
>
> Jiangjie (Becket) Qin
>
>
>
> On Fri, Nov 23, 2018 at 11:25 PM Piotr Nowojski <piotr@xxxxxxxxxxxxxxxxx>
> wrote:
>
> > Hi Becket,
> >
> > Ops, sorry I didn’t notice that you intend to reuse existing
> > `TableFactory`. I don’t know why, but I assumed that you want to provide
> an
> > alternate way of writing the data.
> >
> > Now that I hopefully understand the proposal, maybe we could rename
> > `cache()` to
> >
> > void materialize()
> >
> > or going step further
> >
> > MaterializedTable materialize()
> > MaterializedTable createMaterializedView()
> >
> > ?
> >
> > The second option with returning a handle I think is more flexible and
> > could provide features such as “refresh”/“delete” or generally speaking
> > manage the the view. In the future we could also think about adding hooks
> > to automatically refresh view etc. It is also more explicit -
> > materialization returning a new table handle will not have the same
> > implicit side effects as adding a simple line of code like `b.cache()`
> > would have.
> >
> > It would also be more SQL like, making it more intuitive for users
> already
> > familiar with the SQL.
> >
> > Piotrek
> >
> > > On 23 Nov 2018, at 14:53, Becket Qin <becket.qin@xxxxxxxxx> wrote:
> > >
> > > Hi Piotrek,
> > >
> > > For the cache() method itself, yes, it is equivalent to creating a
> > BUILT-IN
> > > materialized view with a lifecycle. That functionality is missing
> today,
> > > though. Not sure if I understand your question. Do you mean we already
> > have
> > > the functionality and just need a syntax sugar?
> > >
> > > What's more interesting in the proposal is do we want to stop at
> creating
> > > the materialized view? Or do we want to extend that in the future to a
> > more
> > > useful unified data store distributed with Flink? And do we want to
> have
> > a
> > > mechanism allow more flexible user job pattern with their own user
> > defined
> > > services. These considerations are much more architectural.
> > >
> > > Thanks,
> > >
> > > Jiangjie (Becket) Qin
> > >
> > > On Fri, Nov 23, 2018 at 6:01 PM Piotr Nowojski <
> piotr@xxxxxxxxxxxxxxxxx>
> > > wrote:
> > >
> > >> Hi,
> > >>
> > >> Interesting idea. I’m trying to understand the problem. Isn’t the
> > >> `cache()` call an equivalent of writing data to a sink and later
> reading
> > >> from it? Where this sink has a limited live scope/live time? And the
> > sink
> > >> could be implemented as in memory or a file sink?
> > >>
> > >> If so, what’s the problem with creating a materialised view from a
> table
> > >> “b” (from your document’s example) and reusing this materialised view
> > >> later? Maybe we are lacking mechanisms to clean up materialised views
> > (for
> > >> example when current session finishes)? Maybe we need some syntactic
> > sugar
> > >> on top of it?
> > >>
> > >> Piotrek
> > >>
> > >>> On 23 Nov 2018, at 07:21, Becket Qin <becket.qin@xxxxxxxxx> wrote:
> > >>>
> > >>> Thanks for the suggestion, Jincheng.
> > >>>
> > >>> Yes, I think it makes sense to have a persist() with
> lifecycle/defined
> > >>> scope. I just added a section in the future work for this.
> > >>>
> > >>> Thanks,
> > >>>
> > >>> Jiangjie (Becket) Qin
> > >>>
> > >>> On Fri, Nov 23, 2018 at 1:55 PM jincheng sun <
> sunjincheng121@xxxxxxxxx
> > >
> > >>> wrote:
> > >>>
> > >>>> Hi Jiangjie,
> > >>>>
> > >>>> Thank you for the explanation about the name of `cache()`, I
> > understand
> > >> why
> > >>>> you designed this way!
> > >>>>
> > >>>> Another idea is whether we can specify a lifecycle for data
> > persistence?
> > >>>> For example, persist (LifeCycle.SESSION), so that the user is not
> > >> worried
> > >>>> about data loss, and will clearly specify the time range for keeping
> > >> time.
> > >>>> At the same time, if we want to expand, we can also share in a
> certain
> > >>>> group of session, for example: LifeCycle.SESSION_GROUP(...), I am
> not
> > >> sure,
> > >>>> just an immature suggestion, for reference only!
> > >>>>
> > >>>> Bests,
> > >>>> Jincheng
> > >>>>
> > >>>> Becket Qin <becket.qin@xxxxxxxxx> 于2018年11月23日周五 下午1:33写道:
> > >>>>
> > >>>>> Re: Jincheng,
> > >>>>>
> > >>>>> Thanks for the feedback. Regarding cache() v.s. persist(),
> > personally I
> > >>>>> find cache() to be more accurately describing the behavior, i.e.
> the
> > >>>> Table
> > >>>>> is cached for the session, but will be deleted after the session is
> > >>>> closed.
> > >>>>> persist() seems a little misleading as people might think the table
> > >> will
> > >>>>> still be there even after the session is gone.
> > >>>>>
> > >>>>> Great point about mixing the batch and stream processing in the
> same
> > >> job.
> > >>>>> We should absolutely move towards that goal. I imagine that would
> be
> > a
> > >>>> huge
> > >>>>> change across the board, including sources, operators and
> > >> optimizations,
> > >>>> to
> > >>>>> name some. Likely we will need several separate in-depth
> discussions.
> > >>>>>
> > >>>>> Thanks,
> > >>>>>
> > >>>>> Jiangjie (Becket) Qin
> > >>>>>
> > >>>>> On Fri, Nov 23, 2018 at 5:14 AM Xingcan Cui <xingcanc@xxxxxxxxx>
> > >> wrote:
> > >>>>>
> > >>>>>> Hi all,
> > >>>>>>
> > >>>>>> @Shaoxuan, I think the lifecycle or access domain are both
> > orthogonal
> > >>>> to
> > >>>>>> the cache problem. Essentially, this may be the first time we plan
> > to
> > >>>>>> introduce another storage mechanism other than the state. Maybe
> it’s
> > >>>>> better
> > >>>>>> to first draw a big picture and then concentrate on a specific
> part?
> > >>>>>>
> > >>>>>> @Becket, yes, actually I am more concerned with the underlying
> > >> service.
> > >>>>>> This seems to be quite a major change to the existing codebase. As
> > you
> > >>>>>> claimed, the service should be extendible to support other
> > components
> > >>>> and
> > >>>>>> we’d better discussed it in another thread.
> > >>>>>>
> > >>>>>> All in all, I also eager to enjoy the more interactive Table API,
> in
> > >>>> case
> > >>>>>> of a general and flexible enough service mechanism.
> > >>>>>>
> > >>>>>> Best,
> > >>>>>> Xingcan
> > >>>>>>
> > >>>>>>> On Nov 22, 2018, at 10:16 AM, Xiaowei Jiang <xiaoweij@xxxxxxxxx>
> > >>>>> wrote:
> > >>>>>>>
> > >>>>>>> Relying on a callback for the temp table for clean up is not very
> > >>>>>> reliable.
> > >>>>>>> There is no guarantee that it will be executed successfully. We
> may
> > >>>>> risk
> > >>>>>>> leaks when that happens. I think that it's safer to have an
> > >>>> association
> > >>>>>>> between temp table and session id. So we can always clean up temp
> > >>>>> tables
> > >>>>>>> which are no longer associated with any active sessions.
> > >>>>>>>
> > >>>>>>> Regards,
> > >>>>>>> Xiaowei
> > >>>>>>>
> > >>>>>>> On Thu, Nov 22, 2018 at 12:55 PM jincheng sun <
> > >>>>> sunjincheng121@xxxxxxxxx>
> > >>>>>>> wrote:
> > >>>>>>>
> > >>>>>>>> Hi Jiangjie&Shaoxuan,
> > >>>>>>>>
> > >>>>>>>> Thanks for initiating this great proposal!
> > >>>>>>>>
> > >>>>>>>> Interactive Programming is very useful and user friendly in case
> > of
> > >>>>> your
> > >>>>>>>> examples.
> > >>>>>>>> Moreover, especially when a business has to be executed in
> several
> > >>>>>> stages
> > >>>>>>>> with dependencies,such as the pipeline of Flink ML, in order to
> > >>>>> utilize
> > >>>>>> the
> > >>>>>>>> intermediate calculation results we have to submit a job by
> > >>>>>> env.execute().
> > >>>>>>>>
> > >>>>>>>> About the `cache()`  , I think is better to named `persist()`,
> And
> > >>>> The
> > >>>>>>>> Flink framework determines whether we internally cache in memory
> > or
> > >>>>>> persist
> > >>>>>>>> to the storage system,Maybe save the data into state backend
> > >>>>>>>> (MemoryStateBackend or RocksDBStateBackend etc.)
> > >>>>>>>>
> > >>>>>>>> BTW, from the points of my view in the future, support for
> > streaming
> > >>>>> and
> > >>>>>>>> batch mode switching in the same job will also benefit in
> > >>>> "Interactive
> > >>>>>>>> Programming",  I am looking forward to your JIRAs and FLIP!
> > >>>>>>>>
> > >>>>>>>> Best,
> > >>>>>>>> Jincheng
> > >>>>>>>>
> > >>>>>>>>
> > >>>>>>>> Becket Qin <becket.qin@xxxxxxxxx> 于2018年11月20日周二 下午9:56写道:
> > >>>>>>>>
> > >>>>>>>>> Hi all,
> > >>>>>>>>>
> > >>>>>>>>> As a few recent email threads have pointed out, it is a
> promising
> > >>>>>>>>> opportunity to enhance Flink Table API in various aspects,
> > >>>> including
> > >>>>>>>>> functionality and ease of use among others. One of the
> scenarios
> > >>>>> where
> > >>>>>> we
> > >>>>>>>>> feel Flink could improve is interactive programming. To explain
> > the
> > >>>>>>>> issues
> > >>>>>>>>> and facilitate the discussion on the solution, we put together
> > the
> > >>>>>>>>> following document with our proposal.
> > >>>>>>>>>
> > >>>>>>>>>
> > >>>>>>>>>
> > >>>>>>>>
> > >>>>>>
> > >>>>>
> > >>>>
> > >>
> >
> https://docs.google.com/document/d/1d4T2zTyfe7hdncEUAxrlNOYr4e5IMNEZLyqSuuswkA0/edit?usp=sharing
> > >>>>>>>>>
> > >>>>>>>>> Feedback and comments are very welcome!
> > >>>>>>>>>
> > >>>>>>>>> Thanks,
> > >>>>>>>>>
> > >>>>>>>>> Jiangjie (Becket) Qin
> > >>>>>>>>>
> > >>>>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>
> > >>>>
> > >>
> > >>
> >
> >
>