py4j looks really nice and the communication works in both ways. There is also another Python to Java communication library called javabridge. I think it is a pity we chose to implement a proprietary protocol for the network communication of the Python API. This could have been abstracted more nicely and we have already seen that you can run into problems if you implement that yourself.
Serializers could be created dynamically if Python passed its dynamically determined types to Java at runtime. Then everything should work on the Java side. On Fri, Jul 31, 2015 at 11:01 AM, Till Rohrmann <trohrm...@apache.org> wrote: > Zeppelin uses py4j [1] to transfer data between a Python process and a JVM. > That way they can run a Python interpreter and Java interpreter and easily > share state between them. Spark also uses py4j as a bridge between Java and > Python. However, I don't know for what exactly. And I also don't know > what's the performance penalty of py4j. But programming is a lot of fun > with it :-) > > Cheers, > Till > > [1] https://www.py4j.org/ > > On Fri, Jul 31, 2015 at 10:34 AM, Stephan Ewen <se...@apache.org> wrote: > > > I think in short: Spark never worried about types. It is just something > > arbitrary. > > > > Flink worries about types, for memory management. > > > > Aljoscha's suggestion is a good one: have a PythonTypeInfo that is > dynamic. > > > > Till' also found a pretty nice way to connect Python and Java in his > > Zeppelin-based demo at the meetup. > > > > On Fri, Jul 31, 2015 at 10:30 AM, Chesnay Schepler <c.schep...@web.de> > > wrote: > > > > > if its just a single array, how would you define group/sort keys? > > > > > > > > > On 31.07.2015 07:03, Aljoscha Krettek wrote: > > > > > >> I think then the Python part would just serialize all the tuple fields > > to > > >> a > > >> big byte array. And all the key fields to another array, so that the > > java > > >> side can to comparisons on the whole "key blob". > > >> > > >> Maybe it's overly simplistic, but it might work. :D > > >> > > >> On Thu, 30 Jul 2015 at 23:35 Chesnay Schepler <c.schep...@web.de> > > wrote: > > >> > > >> I can see this working for basic types, but am unsure how it would > work > > >>> with Tuples. Wouldn't the java API still need to know the arity to > > setup > > >>> serializers? > > >>> > > >>> On 30.07.2015 23:02, Aljoscha Krettek wrote: > > >>> > > >>>> I believe it should be possible to create a special PythonTypeInfo > > where > > >>>> the python side is responsible for serializing data to a byte array > > and > > >>>> > > >>> to > > >>> > > >>>> the java side it is just a byte array and all the comparisons are > also > > >>>> performed on these byte arrays. I think partitioning and sort should > > >>>> > > >>> still > > >>> > > >>>> work, since the sorting is (in most cases) only used to group the > > >>>> > > >>> elements > > >>> > > >>>> for a groupBy(). If proper sort order would be required this would > > have > > >>>> > > >>> to > > >>> > > >>>> be done on the python side. > > >>>> > > >>>> On Thu, 30 Jul 2015 at 22:21 Chesnay Schepler <c.schep...@web.de> > > >>>> wrote: > > >>>> > > >>>> To be perfectly honest i never really managed to work my way through > > >>>>> Spark's python API, it's a whole bunch of magic to me; not even the > > >>>>> general structure is understandable. > > >>>>> > > >>>>> With "pure python" do you mean doing everything in python? as in > just > > >>>>> having serialized data on the java side? > > >>>>> > > >>>>> I believe the way to do this with Flink is to add a switch that > > >>>>> a) disables all type checks > > >>>>> b) creates serializers dynamically at runtime. > > >>>>> > > >>>>> a) should be fairly straight forward, b) on the other hand.... > > >>>>> > > >>>>> btw., the Python API itself doesn't require the type information, > it > > >>>>> already does the b part. > > >>>>> > > >>>>> On 30.07.2015 22:11, Gyula Fóra wrote: > > >>>>> > > >>>>>> That I understand, but could you please tell me how is this done > > >>>>>> differently in Spark for instance? > > >>>>>> > > >>>>>> What would we need to change to make this work with pure python > (as > > it > > >>>>>> seems to be possible)? This probably have large performance > > >>>>>> > > >>>>> implications > > >>> > > >>>> though. > > >>>>>> > > >>>>>> Gyula > > >>>>>> > > >>>>>> Chesnay Schepler <c.schep...@web.de> ezt írta (időpont: 2015. > júl. > > >>>>>> > > >>>>> 30., > > >>> > > >>>> Cs, > > >>>>> > > >>>>>> 22:04): > > >>>>>> > > >>>>>> because it still goes through the Java API that requires some kind > > of > > >>>>>>> type information. imagine a java api program where you omit all > > >>>>>>> > > >>>>>> generic > > >>> > > >>>> types, it just wouldn't work as of now. > > >>>>>>> > > >>>>>>> On 30.07.2015 21:17, Gyula Fóra wrote: > > >>>>>>> > > >>>>>>>> Hey! > > >>>>>>>> > > >>>>>>>> Could anyone briefly tell me what exactly is the reason why we > > force > > >>>>>>>> > > >>>>>>> the > > >>>>> > > >>>>>> users in the Python API to declare types for operators? > > >>>>>>>> > > >>>>>>>> I don't really understand how this works in different systems > but > > I > > >>>>>>>> > > >>>>>>> am > > >>> > > >>>> just > > >>>>>>> > > >>>>>>>> curious why Flink has types and why Spark doesn't for instance. > > >>>>>>>> > > >>>>>>>> If you give me some pointers to read that would also be fine :) > > >>>>>>>> > > >>>>>>>> Thank you, > > >>>>>>>> Gyula > > >>>>>>>> > > >>>>>>>> > > >>> > > > > > >
