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://nam11.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%7C7f0d8171d15848afb10c08d7eb215530%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637236400701707166&sdata=1qauveOMB1lKHSkRco7v8tBpcJXab8IeGlcoYNMCZ%2BU%3D&reserved=0 > > > [2] > > > > https://nam11.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%7C7f0d8171d15848afb10c08d7eb215530%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637236400701707166&sdata=%2B9TrlfiGSWDnsaT8DMPrSn1CqGIxtgfNLcPFRJ%2F%2FANQ%3D&reserved=0 > > > [3] > > > > https://nam11.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%7C7f0d8171d15848afb10c08d7eb215530%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637236400701707166&sdata=EjocqFcoIho43wU3yvOEO9Vtvn2jTHliV88W%2BSOed9k%3D&reserved=0 > > > [4] > > > > https://nam11.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%7C7f0d8171d15848afb10c08d7eb215530%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637236400701707166&sdata=BpMYD30%2B2tXeaoIj0nNhlho8XUZOEYvT%2FzH%2FJ4WEK98%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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fapache%2Fspark%2Fpull%2F28085%23discussion_r407334754&data=02%7C01%7C%7C7f0d8171d15848afb10c08d7eb215530%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637236400701707166&sdata=6A82CT7n4FwG6f1Hx3%2FqmetQVSGWlrcE7BHDx0LLwTo%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 > > > > >> > > > > > > > > >
