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From Stephan Ewen <se...@apache.org>
Subject Re: Tuple
Date Sun, 02 Aug 2015 22:48:46 GMT
Tuple0 would need special serialization and comparator logic. If that is
given, I see no reason not to support it.

There is BTW, the request to create a dedicated "flink-tuple" project, that
only contains the tuple classes. Any opinions on that?

On Mon, Aug 3, 2015 at 12:45 AM, Matthias J. Sax <
mjsax@informatik.hu-berlin.de> wrote:

> Thanks for the explanation!
>
> As I mentioned before, Tuple0 might also be helpful for streaming. And I
> guess I will need it for Storm compatibility layer, too. (I need to
> double check, but Storm supports zero-attribute-tuples, too).
>
> With regard to the information I collected during the discussion, I vote
> for keeping Tuple0 in Flink core, and fix the serialization problem.
> Should we have another JIRA for this? Or should I extend the existing
> JIRA? (https://issues.apache.org/jira/browse/FLINK-2457)
>
> -Matthias
>
>
> On 08/03/2015 12:22 AM, Chesnay Schepler wrote:
> > First of all, it was a really good idea to start a discussion about this.
> >
> > So the general idea behind Tuple0 was this:
> >
> > The Python API maps python tuples to flink tuples. Python can have empty
> > tuples, so i thought "well duh, let's make a Tuple0 class!". What i did
> > not wanna do is create some non-Tuple object to represent empty tuples,
> > I'd rather have them treated the same, because it's less work and
> > creates simpler code.
> >
> > When transferring the plan to java, certain parameters for operations
> > are tuples, which can be empty aswell.
> > This is where the Tuple0 class is really useful, because these empty
> > tuples go through the same logic as other tuples.
> > This is also why i want to keep the class, at least in the python
> > project, for now.
> >
> > For the actual program execution, I need a new solution. Funny story,
> > while writing this reply i noticed that the Python API can't handle
> > Tuple0 at runtime aswell. ha...ha... -.-
> >
> > Guess I now know what I'm working on next.
> >
> > On 02.08.2015 21:24, Matthias J. Sax wrote:
> >> Can you elaborate how and why Python used Tuple0? If it cannot be
> >> serialized similar to regular Tuples, what is the usage in Python? Right
> >> now it seems, as there is no special serialization code for Tuple0.
> >>
> >> I just want to understand the topic in detail.
> >>
> >> -Matthias
> >>
> >>
> >> On 08/01/2015 03:38 PM, Stephan Ewen wrote:
> >>> I think a Tuple0 cannot be implemented like the current tuples, at
> least
> >>> with respect to runtime serialization.
> >>>
> >>> The system makes the assumption that it makes progress in consuming
> >>> bytes
> >>> when deserializing values. If a Tuple= never consumes data from the
> byte
> >>> stream, this assumption is broken. It would need at least one marker
> >>> byte.
> >>> Then it effectively is a Tuple1<Byte> disgusing itself as a tuple0.
> >>>
> >>>
> >>>
> >>> On Sat, Aug 1, 2015 at 1:38 PM, Matthias J. Sax <
> >>> mjsax@informatik.hu-berlin.de> wrote:
> >>>
> >>>> I just double checked. Scala does not have type Tuple0. IMHO, it would
> >>>> be best to remove Tuple0 for consistency. Having Tuple types is for
> >>>> consistency reason with Scala in the first place, right? Please give
> >>>> feedback.
> >>>>
> >>>> -Matthias
> >>>>
> >>>>
> >>>> On 08/01/2015 01:04 PM, Matthias J. Sax wrote:
> >>>>> I see.
> >>>>>
> >>>>> I think that it might be useful to have Tuple0, because in rare
> cases,
> >>>>> you only want to "notify" a downstream operators (taking about
> >>>>> streaming) that something happened but there is no actual data to
be
> >>>>> processed. Furthermore, if Flink cannot deal with Tuple0 it should
be
> >>>>> removed completely for consistency IMHO.
> >>>>>
> >>>>> I will open a JIRA for it.
> >>>>>
> >>>>> -Matthias
> >>>>>
> >>>>> On 07/31/2015 10:44 PM, Chesnay Schepler wrote:
> >>>>>> also, I'm not sure if I ever sent a Tuple0 through a program,
it
> >>>>>> could
> >>>>>> be that the system freaks out.
> >>>>>>
> >>>>>> On 31.07.2015 22:40, Chesnay Schepler wrote:
> >>>>>>> there's no specific reason. it was added fairly recently
by me
> >>>>>>> (mid of
> >>>>>>> april), and you're most likely the second person to use
it.
> >>>>>>>
> >>>>>>> i didn't integrate into all our tuple related stuff because,
well,
> i
> >>>>>>> never thought anyone would actually need it, so i saved
myself the
> >>>>>>> trouble.
> >>>>>>>
> >>>>>>>> Hi,
> >>>>>>>>
> >>>>>>>> is there any specific reason, why Tuple.getTupleClass(int
arity)
> >>>>>>>> does
> >>>>>>>> not support arity zero? There is a class Tuple0, but
it cannot be
> >>>>>>>> generator by Tuple.getTupleClass(...). Is it a missing
feature (I
> >>>> would
> >>>>>>>> like to have it).
> >>>>>>>>
> >>>>>>>> -Matthias
> >>>>>>>>
> >>>>>>>
> >>>>
> >
>
>

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