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 >>>>>>>> >>>>>>> >>>> >
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