Nothing is urgent. I just don't want to leave it undecided and just keep adding Java APIs inconsistently as it's currently happening.
We should have a set of coherent APIs. It's very difficult to change APIs once they are out in releases. I guess I have seen people here agree with having a general guidance for the same reason at least - please let me know if I'm taking it wrong. I don't think we should assume Java programmers know how Scala works with Java types. Less assumtion might be better. I feel like we have things on the table to consider at this moment and not much point of waiting indefinitely. But sure maybe I am wrong. We can wait for more feedback for a couple of days. On Thu, 30 Apr 2020, 18:59 ZHANG Wei, <wezh...@outlook.com> wrote: > I feel a little pushed... :-) I still don't get the point of why it's > urgent to make the decision now. AFAIK, it's a common practice to handle > Scala types conversions by self when Java programmers prepare to > invoke Scala libraries. I'm not sure which one is the Java programmers' > root complaint, Scala type instance or Scala Jar file. > > My 2 cents. > > -- > Cheers, > -z > > On Thu, 30 Apr 2020 09:17:37 +0900 > Hyukjin Kwon <gurwls...@gmail.com> wrote: > > > There was a typo in the previous email. I am re-sending: > > > > Hm, I thought you meant you prefer 3. over 4 but don't mind particularly. > > I don't mean to wait for more feedback. It looks likely just a deadlock > > which will be the worst case. > > I was suggesting to pick one way first, and stick to it. If we find out > > something later, we can discuss > > more about changing it later. > > > > Having separate Java specific API (3. way) > > - causes maintenance cost > > - makes users to search which API for Java every time > > - this looks the opposite why against the unified API set Spark > targeted > > so far. > > > > I don't completely buy the argument about Scala/Java friendly because > using > > Java instance is already documented in the official Scala documentation. > > Users still need to search if we have Java specific methods for *some* > APIs. > > > > 2020년 4월 30일 (목) 오전 8:58, Hyukjin Kwon <gurwls...@gmail.com>님이 작성: > > > > > Hm, I thought you meant you prefer 3. over 4 but don't mind > particularly. > > > I don't mean to wait for more feedback. It looks likely just a deadlock > > > which will be the worst case. > > > I was suggesting to pick one way first, and stick to it. If we find out > > > something later, we can discuss > > > more about changing it later. > > > > > > Having separate Java specific API (4. way) > > > - causes maintenance cost > > > - makes users to search which API for Java every time > > > - this looks the opposite why against the unified API set Spark > targeted > > > so far. > > > > > > I don't completely buy the argument about Scala/Java friendly because > > > using Java instance is already documented in the official Scala > > > documentation. > > > Users still need to search if we have Java specific methods for *some* > > > APIs. > > > > > > > > > > > > On Thu, 30 Apr 2020, 00:06 Tom Graves, <tgraves...@yahoo.com> wrote: > > > > > >> Sorry I'm not sure what your last email means. Does it mean you are > > >> putting it up for a vote or just waiting to get more feedback? I > disagree > > >> with saying option 4 is the rule but agree having a general rule makes > > >> sense. I think we need a lot more input to make the rule as it > affects the > > >> api's. > > >> > > >> Tom > > >> > > >> On Wednesday, April 29, 2020, 09:53:22 AM CDT, Hyukjin Kwon < > > >> gurwls...@gmail.com> wrote: > > >> > > >> > > >> I think I am not seeing explicit objection here but rather see people > > >> tend to agree with the proposal in general. > > >> I would like to step forward rather than leaving it as a deadlock - > the > > >> worst choice here is to postpone and abandon this discussion with this > > >> inconsistency. > > >> > > >> I don't currently target to document this as the cases are rather > > >> rare, and we haven't really documented JavaRDD <> RDD vs DataFrame > case as > > >> well. > > >> Let's keep monitoring and see if this discussion thread clarifies > things > > >> enough in such cases I mentioned. > > >> > > >> Let me know if you guys think differently. > > >> > > >> > > >> 2020년 4월 28일 (화) 오후 5:03, Hyukjin Kwon <gurwls...@gmail.com>님이 작성: > > >> > > >> Spark has targeted to have a unified API set rather than having > separate > > >> Java classes to reduce the maintenance cost, > > >> e.g.) JavaRDD <> RDD vs DataFrame. These JavaXXX are more about the > > >> legacy. > > >> > > >> I think it's best to stick to the approach 4. in general cases. > > >> Other options might have to be considered based upon a specific > context. > > >> For example, if we *must* to add a bunch of Java-specifics > > >> into a specific class for an inevitable reason somewhere, I would > > >> consider to have a Java-specific class. > > >> > > >> > > >> > > >> 2020년 4월 28일 (화) 오후 4:38, ZHANG Wei <wezh...@outlook.com>님이 작성: > > >> > > >> Be frankly, I also love the pure Java type in Java API and Scala type > in > > >> Scala API. :-) > > >> > > >> If we don't treat Java as a "FRIEND" of Scala, just as Python, maybe > we > > >> can adopt the status of option 1, the specific Java classes. (But I > don't > > >> like the `Java` prefix, which is redundant when I'm coding Java app, > > >> such as JavaRDD, why not distinct it by package namespace...) The > specific > > >> Java API can also leverage some native Java language features with new > > >> versions. > > >> > > >> And just since the friendly relationship between Scala and Java, the > Java > > >> user can call Scala API with `.asScala` or `.asJava`'s help if Java > API > > >> is not ready. Then switch to Java API when it's well cooked. > > >> > > >> The cons is more efforts to maintain. > > >> > > >> My 2 cents. > > >> > > >> -- > > >> Cheers, > > >> -z > > >> > > >> On Tue, 28 Apr 2020 12:07:36 +0900 > > >> Hyukjin Kwon <gurwls...@gmail.com> wrote: > > >> > > >> > The problem is that calling Scala instances in Java side is > discouraged > > >> in > > >> > general up to my best knowledge. > > >> > A Java user won't likely know asJava in Scala but a Scala user will > > >> likely > > >> > know both asScala and asJava. > > >> > > > >> > > > >> > 2020년 4월 28일 (화) 오전 11:35, ZHANG Wei <wezh...@outlook.com>님이 작성: > > >> > > > >> > > How about making a small change on option 4: > > >> > > Keep Scala API returning Scala type instance with providing a > > >> > > `asJava` method to return a Java type instance. > > >> > > > > >> > > Scala 2.13 has provided CollectionConverter [1][2][3], in the > > >> following > > >> > > Spark dependences upgrade, which can be supported by nature. For > > >> > > current Scala 2.12 version, we can wrap > `ImplicitConversionsToJava`[4] > > >> > > as what Scala 2.13 does and add implicit conversions. > > >> > > > > >> > > Just my 2 cents. > > >> > > > > >> > > -- > > >> > > Cheers, > > >> > > -z > > >> > > > > >> > > [1] > > >> > > > > >> > https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.scala-lang.org%2Foverviews%2Fcollections-2.13%2Fconversions-between-java-and-scala-collections.html&data=02%7C01%7C%7C9175b84aa9004ee6da1908d7ec9bea50%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637238026695625983&sdata=Vw8k4x0D0P1Pocr17O6wPUQzt%2FS3iX0lCBigIKdy0yY%3D&reserved=0 > > >> > > [2] > > >> > > > > >> > https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.scala-lang.org%2Fapi%2F2.13.0%2Fscala%2Fjdk%2Fjavaapi%2FCollectionConverters%24.html&data=02%7C01%7C%7C9175b84aa9004ee6da1908d7ec9bea50%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637238026695625983&sdata=9R96UT1W05Wn6K3RhhkMi1lo6bUnHht3qEhKxsr7%2FI0%3D&reserved=0 > > >> > > [3] > > >> > > > > >> > https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.scala-lang.org%2Fapi%2F2.13.0%2Fscala%2Fjdk%2FCollectionConverters%24.html&data=02%7C01%7C%7C9175b84aa9004ee6da1908d7ec9bea50%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637238026695625983&sdata=IBKGT2uSOgMg0KQOLZnDkxMVeUiZDzEvKvxNF%2FZzXxs%3D&reserved=0 > > >> > > [4] > > >> > > > > >> > https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.scala-lang.org%2Fapi%2F2.12.11%2Fscala%2Fcollection%2Fconvert%2FImplicitConversionsToJava%24.html&data=02%7C01%7C%7C9175b84aa9004ee6da1908d7ec9bea50%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637238026695625983&sdata=nkxkT0WUrqpaOUcyvWDDlFK3yrTa7WJBlTw%2Foqjqqks%3D&reserved=0 > > >> > > > > >> > > > > >> > > On Tue, 28 Apr 2020 08:52:57 +0900 > > >> > > Hyukjin Kwon <gurwls...@gmail.com> wrote: > > >> > > > > >> > > > I would like to make sure I am open for other options that can > be > > >> > > > considered situationally and based on the context. > > >> > > > It's okay, and I don't target to restrict this here. For > example, > > >> DSv2, I > > >> > > > understand it's written in Java because Java > > >> > > > interfaces arguably brings better performance. That's why > vectorized > > >> > > > readers are written in Java too. > > >> > > > > > >> > > > Maybe the "general" wasn't explicit in my previous email. Adding > > >> APIs to > > >> > > > return a Java instance is still > > >> > > > rather rare in general given my few years monitoring. > > >> > > > The problem I would more like to deal with is more about when we > > >> need to > > >> > > > add one or a couple of user-facing > > >> > > > Java-specific APIs to return Java instances, which is relatively > > >> more > > >> > > > frequent compared to when we need a bunch > > >> > > > of Java specific APIs. > > >> > > > > > >> > > > In this case, I think it should be guided to use 4. approach. > There > > >> are > > >> > > > pros and cons between 3. and 4., of course. > > >> > > > But it looks to me 4. approach is closer to what Spark has > targeted > > >> so > > >> > > far. > > >> > > > > > >> > > > > > >> > > > > > >> > > > 2020년 4월 28일 (화) 오전 8:34, Hyukjin Kwon <gurwls...@gmail.com>님이 > 작성: > > >> > > > > > >> > > > > > One thing we could do here is use Java collections > internally > > >> and > > >> > > make > > >> > > > > the Scala API a thin wrapper around Java -- like how Python > works. > > >> > > > > > Then adding a method to the Scala API would require adding > it > > >> to the > > >> > > > > Java API and we would keep the two more in sync. > > >> > > > > > > >> > > > > I think it can be an appropriate idea for when we have to deal > > >> with > > >> > > this > > >> > > > > case a lot but I don't think there are so many > > >> > > > > user-facing APIs to return a Java collections, it's rather > rare. > > >> Also, > > >> > > the > > >> > > > > Java users are relatively less than Scala users. > > >> > > > > This case is slightly different from Python in a way that > there > > >> are so > > >> > > > > many differences to deal with in PySpark case. > > >> > > > > > > >> > > > > Also, in case of `Seq`, actually we can just use `Array` > instead > > >> for > > >> > > both > > >> > > > > Scala and Java side simply. I don't find such cases notably > > >> awkward. > > >> > > > > This problematic cases might be specific to few Java > collections > > >> or > > >> > > > > instances, and I would like to avoid an overkill here. > > >> > > > > > > >> > > > > Of course, if there is a place to consider other options, > let's > > >> do. I > > >> > > > > don't like to say this is the only required option. > > >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > 2020년 4월 28일 (화) 오전 1:18, Ryan Blue <rb...@netflix.com.invalid > >님이 > > >> 작성: > > >> > > > > > > >> > > > >> I think the right choice here depends on how the object is > used. > > >> For > > >> > > > >> developer and internal APIs, I think standardizing on Java > > >> collections > > >> > > > >> makes the most sense. > > >> > > > >> > > >> > > > >> For user-facing APIs, it is awkward to return Java > collections to > > >> > > Scala > > >> > > > >> code -- I think that's the motivation for Tom's comment. For > user > > >> > > APIs, I > > >> > > > >> think most methods should return Scala collections, and I > don't > > >> have a > > >> > > > >> strong opinion about whether the conversion (or lack > thereof) is > > >> done > > >> > > in a > > >> > > > >> separate object (#1) or in parallel methods (#3). > > >> > > > >> > > >> > > > >> Both #1 and #3 seem like about the same amount of work and > have > > >> the > > >> > > same > > >> > > > >> likelihood that a developer will leave out a Java method > > >> version. One > > >> > > thing > > >> > > > >> we could do here is use Java collections internally and make > the > > >> > > Scala API > > >> > > > >> a thin wrapper around Java -- like how Python works. Then > adding > > >> a > > >> > > method > > >> > > > >> to the Scala API would require adding it to the Java API and > we > > >> would > > >> > > keep > > >> > > > >> the two more in sync. It would also help avoid Scala > collections > > >> > > leaking > > >> > > > >> into internals. > > >> > > > >> > > >> > > > >> On Mon, Apr 27, 2020 at 8:49 AM Hyukjin Kwon < > > >> gurwls...@gmail.com> > > >> > > wrote: > > >> > > > >> > > >> > > > >>> Let's stick to the less maintenance efforts then rather > than we > > >> > > leave it > > >> > > > >>> undecided and delay with leaving this inconsistency. > > >> > > > >>> > > >> > > > >>> I dont think we can have some very meaningful data about > this > > >> soon > > >> > > given > > >> > > > >>> that we don't hear much complaints about this in general so > far. > > >> > > > >>> > > >> > > > >>> The point of this thread is to make a call rather then > defer to > > >> the > > >> > > > >>> future. > > >> > > > >>> > > >> > > > >>> On Mon, 27 Apr 2020, 23:15 Wenchen Fan, < > cloud0...@gmail.com> > > >> wrote: > > >> > > > >>> > > >> > > > >>>> IIUC We are moving away from having 2 classes for Java and > > >> Scala, > > >> > > like > > >> > > > >>>> JavaRDD and RDD. It's much simpler to maintain and use > with a > > >> > > single class. > > >> > > > >>>> > > >> > > > >>>> I don't have a strong preference over option 3 or 4. We may > > >> need to > > >> > > > >>>> collect more data points from actual users. > > >> > > > >>>> > > >> > > > >>>> On Mon, Apr 27, 2020 at 9:50 PM Hyukjin Kwon < > > >> gurwls...@gmail.com> > > >> > > > >>>> wrote: > > >> > > > >>>> > > >> > > > >>>>> Scala users are arguably more prevailing compared to Java > > >> users, > > >> > > yes. > > >> > > > >>>>> Using the Java instances in Scala side is legitimate, and > > >> they are > > >> > > > >>>>> already being used in multiple please. I don't believe > Scala > > >> > > > >>>>> users find this not Scala friendly as it's legitimate and > > >> already > > >> > > > >>>>> being used. I personally find it's more trouble some to > let > > >> Java > > >> > > > >>>>> users to search which APIs to call. Yes, I understand the > > >> pros and > > >> > > > >>>>> cons - we should also find the balance considering the > actual > > >> > > usage. > > >> > > > >>>>> > > >> > > > >>>>> One more argument from me is, though, I think one of the > > >> goals in > > >> > > > >>>>> Spark APIs is the unified API set up to my knowledge > > >> > > > >>>>> e.g., JavaRDD <> RDD vs DataFrame. > > >> > > > >>>>> If either way is not particularly preferred over the > other, I > > >> would > > >> > > > >>>>> just choose the one to have the unified API set. > > >> > > > >>>>> > > >> > > > >>>>> > > >> > > > >>>>> > > >> > > > >>>>> 2020년 4월 27일 (월) 오후 10:37, Tom Graves < > tgraves...@yahoo.com>님이 > > >> 작성: > > >> > > > >>>>> > > >> > > > >>>>>> I agree a general guidance is good so we keep consistent > in > > >> the > > >> > > apis. > > >> > > > >>>>>> I don't necessarily agree that 4 is the best solution > > >> though. I > > >> > > agree its > > >> > > > >>>>>> nice to have one api, but it is less friendly for the > scala > > >> side. > > >> > > > >>>>>> Searching for the equivalent Java api shouldn't be hard > as it > > >> > > should be > > >> > > > >>>>>> very close in the name and if we make it a general rule > users > > >> > > should > > >> > > > >>>>>> understand it. I guess one good question is what API do > > >> most of > > >> > > our users > > >> > > > >>>>>> use between Java and Scala and what is the ratio? I > don't > > >> know > > >> > > the answer > > >> > > > >>>>>> to that. I've seen more using Scala over Java. If the > > >> majority > > >> > > use Scala > > >> > > > >>>>>> then I think the API should be more friendly to that. > > >> > > > >>>>>> > > >> > > > >>>>>> Tom > > >> > > > >>>>>> > > >> > > > >>>>>> On Monday, April 27, 2020, 04:04:28 AM CDT, Hyukjin Kwon > < > > >> > > > >>>>>> gurwls...@gmail.com> wrote: > > >> > > > >>>>>> > > >> > > > >>>>>> > > >> > > > >>>>>> Hi all, > > >> > > > >>>>>> > > >> > > > >>>>>> I would like to discuss Java specific APIs and which > design > > >> we > > >> > > will > > >> > > > >>>>>> choose. > > >> > > > >>>>>> This has been discussed in multiple places so far, for > > >> example, at > > >> > > > >>>>>> > > >> > https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fapache%2Fspark%2Fpull%2F28085%23discussion_r407334754&data=02%7C01%7C%7C9175b84aa9004ee6da1908d7ec9bea50%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637238026695625983&sdata=zEYDV0XyvDbeL5YojcdZWHfuJ%2BVOP5%2ByFlbkTFlHPGM%3D&reserved=0 > > >> > > > >>>>>> > > >> > > > >>>>>> > > >> > > > >>>>>> *The problem:* > > >> > > > >>>>>> > > >> > > > >>>>>> In short, I would like us to have clear guidance on how > we > > >> support > > >> > > > >>>>>> Java specific APIs when > > >> > > > >>>>>> it requires to return a Java instance. The problem is > simple: > > >> > > > >>>>>> > > >> > > > >>>>>> def requests: Map[String, ExecutorResourceRequest] = ... > > >> > > > >>>>>> def requestsJMap: java.util.Map[String, > > >> ExecutorResourceRequest] > > >> > > = ... > > >> > > > >>>>>> > > >> > > > >>>>>> vs > > >> > > > >>>>>> > > >> > > > >>>>>> def requests: java.util.Map[String, > ExecutorResourceRequest] > > >> = ... > > >> > > > >>>>>> > > >> > > > >>>>>> > > >> > > > >>>>>> *Current codebase:* > > >> > > > >>>>>> > > >> > > > >>>>>> My understanding so far was that the latter is preferred > and > > >> more > > >> > > > >>>>>> consistent and prevailing in the > > >> > > > >>>>>> existing codebase, for example, see > StateOperatorProgress and > > >> > > > >>>>>> StreamingQueryProgress in Structured Streaming. > > >> > > > >>>>>> However, I realised that we also have other approaches > in the > > >> > > current > > >> > > > >>>>>> codebase. There look > > >> > > > >>>>>> four approaches to deal with Java specifics in general: > > >> > > > >>>>>> > > >> > > > >>>>>> 1. Java specific classes such as JavaRDD and > > >> JavaSparkContext. > > >> > > > >>>>>> 2. Java specific methods with the same name that > overload > > >> its > > >> > > > >>>>>> parameters, see functions.scala. > > >> > > > >>>>>> 3. Java specific methods with a different name that > needs > > >> to > > >> > > > >>>>>> return a different type such as > TaskContext.resourcesJMap > > >> vs > > >> > > > >>>>>> TaskContext.resources. > > >> > > > >>>>>> 4. One method that returns a Java instance for both > Scala > > >> and > > >> > > > >>>>>> Java sides. see StateOperatorProgress and > > >> > > StreamingQueryProgress. > > >> > > > >>>>>> > > >> > > > >>>>>> > > >> > > > >>>>>> *Analysis on the current codebase:* > > >> > > > >>>>>> > > >> > > > >>>>>> I agree with 2. approach because the corresponding cases > > >> give you > > >> > > a > > >> > > > >>>>>> consistent API usage across > > >> > > > >>>>>> other language APIs in general. Approach 1. is from the > old > > >> world > > >> > > > >>>>>> when we didn't have unified APIs. > > >> > > > >>>>>> This might be the worst approach. > > >> > > > >>>>>> > > >> > > > >>>>>> 3. and 4. are controversial. > > >> > > > >>>>>> > > >> > > > >>>>>> For 3., if you have to use Java APIs, then, you should > > >> search if > > >> > > > >>>>>> there is a variant of that API > > >> > > > >>>>>> every time specifically for Java APIs. But yes, it gives > you > > >> > > > >>>>>> Java/Scala friendly instances. > > >> > > > >>>>>> > > >> > > > >>>>>> For 4., having one API that returns a Java instance > makes you > > >> > > able to > > >> > > > >>>>>> use it in both Scala and Java APIs > > >> > > > >>>>>> sides although it makes you call asScala in Scala side > > >> > > specifically. > > >> > > > >>>>>> But you don’t > > >> > > > >>>>>> have to search if there’s a variant of this API and it > gives > > >> you a > > >> > > > >>>>>> consistent API usage across languages. > > >> > > > >>>>>> > > >> > > > >>>>>> Also, note that calling Java in Scala is legitimate but > the > > >> > > opposite > > >> > > > >>>>>> case is not, up to my best knowledge. > > >> > > > >>>>>> In addition, you should have a method that returns a Java > > >> instance > > >> > > > >>>>>> for PySpark or SparkR to support. > > >> > > > >>>>>> > > >> > > > >>>>>> > > >> > > > >>>>>> *Proposal:* > > >> > > > >>>>>> > > >> > > > >>>>>> I would like to have a general guidance on this that the > > >> Spark dev > > >> > > > >>>>>> agrees upon: Do 4. approach. If not possible, do 3. > Avoid 1 > > >> > > almost at all > > >> > > > >>>>>> cost. > > >> > > > >>>>>> > > >> > > > >>>>>> Note that this isn't a hard requirement but *a general > > >> guidance*; > > >> > > > >>>>>> therefore, the decision might be up to > > >> > > > >>>>>> the specific context. For example, when there are some > strong > > >> > > > >>>>>> arguments to have a separate Java specific API, that’s > fine. > > >> > > > >>>>>> Of course, we won’t change the existing methods given > > >> Micheal’s > > >> > > > >>>>>> rubric added before. I am talking about new > > >> > > > >>>>>> methods in unreleased branches. > > >> > > > >>>>>> > > >> > > > >>>>>> Any concern or opinion on this? > > >> > > > >>>>>> > > >> > > > >>>>> > > >> > > > >> > > >> > > > >> -- > > >> > > > >> Ryan Blue > > >> > > > >> Software Engineer > > >> > > > >> Netflix > > >> > > > >> > > >> > > > > > > >> > > > > >> > > >> >
