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 < mj...@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 < > >>> mj...@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 > >>>>>>>> > >>>>>>> > >>>> > > > >
