Hi Timo and Vino, I agree that table is very active and there is no guarantee for not producing any conflicts if you decide to develop based on community version. I think this part is the risk what we can imagine in the first place. But massively language replacing is something you can not imagine and be ready for, there is no feature added, no refactor is done, simply changing from scala to java will cause lots of conflicts.
But I also agree that this is a "technical debt" that we should eventually pay, as you said, we can do this slowly, even one file each time, let other people have more time to resolve the conflicts. Best, Kurt On Tue, Nov 27, 2018 at 8:37 PM Timo Walther <twal...@apache.org> wrote: > Hi Kurt, > > I understand your concerns. However, there is no concrete roadmap for > Flink 2.0 and (as Vino said) the flink-table is developed very actively. > Major refactorings happened in the past and will also happen with or > without Scala migration. A good example, is the proper catalog support > which will refactor big parts of the TableEnvironment class. Or the > introduction of "retractions" which needed a big refactoring of the > planning phase. Stability is only guaranteed for the API and the general > behavior, however, currently flink-table is not using @Public or > @PublicEvolving annotations for a reason. > > I think the migration will still happen slowly because it needs people > that allocate time for that. Therefore, even Flink forks can slowly > adapt to the evolving Scala-to-Java code base. > > Regards, > Timo > > > Am 27.11.18 um 13:16 schrieb vino yang: > > Hi Kurt, > > > > Currently, there is still a long time to go from flink 2.0. Considering > > that the flink-table > > is one of the most active modules in the current flink project, each > > version has > > a number of changes and features added. I think that refactoring faster > > will reduce subsequent > > complexity and workload. And this may be a gradual and long process. We > > should be able to > > regard it as a "technical debt", and if it does not change it, it will > > also affect the decision-making of other issues. > > > > Thanks, vino. > > > > Kurt Young <ykt...@gmail.com> 于2018年11月27日周二 下午7:34写道： > > > >> Hi Timo, > >> > >> Thanks for writing up the document. I'm +1 for reorganizing the module > >> structure and make table scala free. But I have > >> a little concern abount the timing. Is it more appropriate to get this > done > >> when Flink decide to bump to next big version, like 2.x. > >> It's true you can keep all the class's package path as it is, and will > not > >> introduce API change. But if some company are developing their own > >> Flink, and sync with community version by rebasing, may face a lot of > >> conflicts. Although you can avoid conflicts by always moving source > codes > >> between packages, but I assume you still need to delete the original > scala > >> file and add a new java file when you want to change program language. > >> > >> Best, > >> Kurt > >> > >> > >> On Tue, Nov 27, 2018 at 5:57 PM Timo Walther <twal...@apache.org> > wrote: > >> > >>> Hi Hequn, > >>> > >>> thanks for your feedback. Yes, migrating the test cases is another > issue > >>> that is not represented in the document but should naturally go along > >>> with the migration. > >>> > >>> I agree that we should migrate the main API classes quickly within this > >>> 1.8 release after the module split has been performed. Help here is > >>> highly appreciated! > >>> > >>> I forgot that Java supports static methods in interfaces now, but > >>> actually I don't like the design of calling > `TableEnvironment.get(env)`. > >>> Because people often use `TableEnvironment tEnd = > >>> TableEnvironment.get(env)` and then wonder why there is no > >>> `toAppendStream` or `toDataSet` because they are using the base class. > >>> However, things like that can be discussed in the corresponding issue > >>> when it comes to implementation. > >>> > >>> @Vino: I think your work fits nicely to these efforts. > >>> > >>> @everyone: I will wait for more feedback until end of this week. Then I > >>> will convert the design document into a FLIP and open subtasks in Jira, > >>> if there are no objections? > >>> > >>> Regards, > >>> Timo > >>> > >>> Am 24.11.18 um 13:45 schrieb vino yang: > >>>> Hi hequn, > >>>> > >>>> I am very glad to hear that you are interested in this work. > >>>> As we all know, this process involves a lot. > >>>> Currently, the migration work has begun. I started with the > >>>> Kafka connector's dependency on flink-table and moved the > >>>> related dependencies to flink-table-common. > >>>> This work is tracked by FLINK-9461. [1] > >>>> I don't know if it will conflict with what you expect to do, but from > >> the > >>>> impact I have observed, > >>>> it will involve many classes that are currently in flink-table. > >>>> > >>>> *Just a statement to prevent unnecessary conflicts.* > >>>> > >>>> Thanks, vino. > >>>> > >>>> [1]: https://issues.apache.org/jira/browse/FLINK-9461 > >>>> > >>>> Hequn Cheng <chenghe...@gmail.com> 于2018年11月24日周六 下午7:20写道： > >>>> > >>>>> Hi Timo, > >>>>> > >>>>> Thanks for the effort and writing up this document. I like the idea > to > >>> make > >>>>> flink-table scala free, so +1 for the proposal! > >>>>> > >>>>> It's good to make Java the first-class citizen. For a long time, we > >> have > >>>>> neglected java so that many features in Table are missed in Java Test > >>>>> cases, such as this one[1] I found recently. And I think we may also > >>> need > >>>>> to migrate our test cases, i.e, add java tests. > >>>>> > >>>>> This definitely is a big change and will break API compatible. In > >> order > >>> to > >>>>> bring a smaller impact on users, I think we should go fast when we > >>> migrate > >>>>> APIs targeted to users. It's better to introduce the user sensitive > >>> changes > >>>>> within a release. However, it may be not that easy. I can help to > >>>>> contribute. > >>>>> > >>>>> Separation of interface and implementation is a good idea. This may > >>>>> introduce a minimum of dependencies or even no dependencies. I saw > >> your > >>>>> reply in the google doc. Java8 has already supported static method > for > >>>>> interfaces, I think we can make use of it? > >>>>> > >>>>> Best, > >>>>> Hequn > >>>>> > >>>>> [1] https://issues.apache.org/jira/browse/FLINK-11001 > >>>>> > >>>>> > >>>>> On Fri, Nov 23, 2018 at 5:36 PM Timo Walther <twal...@apache.org> > >>> wrote: > >>>>>> Hi everyone, > >>>>>> > >>>>>> thanks for the great feedback so far. I updated the document with > the > >>>>>> input I got so far > >>>>>> > >>>>>> @Fabian: I moved the porting of flink-table-runtime classes up in > the > >>>>> list. > >>>>>> @Xiaowei: Could you elaborate what "interface only" means to you? Do > >>> you > >>>>>> mean a module containing pure Java `interface`s? Or is the > validation > >>>>>> logic also part of the API module? Are 50+ expression classes part > of > >>>>>> the API interface or already too implementation-specific? > >>>>>> > >>>>>> @Xuefu: I extended the document by almost a page to clarify when we > >>>>>> should develop in Scala and when in Java. As Piotr said, every new > >>> Scala > >>>>>> line is instant technical debt. > >>>>>> > >>>>>> Thanks, > >>>>>> Timo > >>>>>> > >>>>>> > >>>>>> Am 23.11.18 um 10:29 schrieb Piotr Nowojski: > >>>>>>> Hi Timo, > >>>>>>> > >>>>>>> Thanks for writing this down +1 from my side :) > >>>>>>> > >>>>>>>> I'm wondering that whether we can have rule in the interim when > >> Java > >>>>>> and Scala coexist that dependency can only be one-way. I found that > >> in > >>>>> the > >>>>>> current code base there are cases where a Scala class extends Java > >> and > >>>>> vise > >>>>>> versa. This is quite painful. I'm thinking if we could say that > >>> extension > >>>>>> can only be from Java to Scala, which will help the situation. > >> However, > >>>>> I'm > >>>>>> not sure if this is practical. > >>>>>>> Xuefu: I’m also not sure what’s the best approach here, probably we > >>>>> will > >>>>>> have to work it out as we go. One thing to consider is that from now > >>> on, > >>>>>> every single new code line written in Scala anywhere in Flink-table > >>>>> (except > >>>>>> of Flink-table-api-scala) is an instant technological debt. From > this > >>>>>> perspective I would be in favour of tolerating quite big > >> inchonvieneces > >>>>>> just to avoid any new Scala code. > >>>>>>> Piotrek > >>>>>>> > >>>>>>>> On 23 Nov 2018, at 03:25, Zhang, Xuefu <xuef...@alibaba-inc.com> > >>>>> wrote: > >>>>>>>> Hi Timo, > >>>>>>>> > >>>>>>>> Thanks for the effort and the Google writeup. During our external > >>>>>> catalog rework, we found much confusion between Java and Scala, and > >>> this > >>>>>> Scala-free roadmap should greatly mitigate that. > >>>>>>>> I'm wondering that whether we can have rule in the interim when > >> Java > >>>>>> and Scala coexist that dependency can only be one-way. I found that > >> in > >>>>> the > >>>>>> current code base there are cases where a Scala class extends Java > >> and > >>>>> vise > >>>>>> versa. This is quite painful. I'm thinking if we could say that > >>> extension > >>>>>> can only be from Java to Scala, which will help the situation. > >> However, > >>>>> I'm > >>>>>> not sure if this is practical. > >>>>>>>> Thanks, > >>>>>>>> Xuefu > >>>>>>>> > >>>>>>>> > >>>>>>>> ------------------------------------------------------------------ > >>>>>>>> Sender:jincheng sun <sunjincheng...@gmail.com> > >>>>>>>> Sent at:2018 Nov 23 (Fri) 09:49 > >>>>>>>> Recipient:dev <dev@flink.apache.org> > >>>>>>>> Subject:Re: [DISCUSS] Long-term goal of making flink-table > >> Scala-free > >>>>>>>> Hi Timo, > >>>>>>>> Thanks for initiating this great discussion. > >>>>>>>> > >>>>>>>> Currently when using SQL/TableAPI should include many dependence. > >> In > >>>>>>>> particular, it is not necessary to introduce the specific > >>>>> implementation > >>>>>>>> dependencies which users do not care about. So I am glad to see > >> your > >>>>>>>> proposal, and hope when we consider splitting the API interface > >> into > >>> a > >>>>>>>> separate module, so that the user can introduce minimum of > >>>>> dependencies. > >>>>>>>> So, +1 to [separation of interface and implementation; e.g. > >> `Table` & > >>>>>>>> `TableImpl`] which you mentioned in the google doc. > >>>>>>>> Best, > >>>>>>>> Jincheng > >>>>>>>> > >>>>>>>> Xiaowei Jiang <xiaow...@gmail.com> 于2018年11月22日周四 下午10:50写道： > >>>>>>>> > >>>>>>>>> Hi Timo, thanks for driving this! I think that this is a nice > >> thing > >>>>> to > >>>>>> do. > >>>>>>>>> While we are doing this, can we also keep in mind that we want to > >>>>>>>>> eventually have a TableAPI interface only module which users can > >>> take > >>>>>>>>> dependency on, but without including any implementation details? > >>>>>>>>> > >>>>>>>>> Xiaowei > >>>>>>>>> > >>>>>>>>> On Thu, Nov 22, 2018 at 6:37 PM Fabian Hueske <fhue...@gmail.com > > > >>>>>> wrote: > >>>>>>>>>> Hi Timo, > >>>>>>>>>> > >>>>>>>>>> Thanks for writing up this document. > >>>>>>>>>> I like the new structure and agree to prioritize the porting of > >> the > >>>>>>>>>> flink-table-common classes. > >>>>>>>>>> Since flink-table-runtime is (or should be) independent of the > >> API > >>>>> and > >>>>>>>>>> planner modules, we could start porting these classes once the > >> code > >>>>> is > >>>>>>>>>> split into the new module structure. > >>>>>>>>>> The benefits of a Scala-free flink-table-runtime would be a > >>>>> Scala-free > >>>>>>>>>> execution Jar. > >>>>>>>>>> > >>>>>>>>>> Best, Fabian > >>>>>>>>>> > >>>>>>>>>> > >>>>>>>>>> Am Do., 22. Nov. 2018 um 10:54 Uhr schrieb Timo Walther < > >>>>>>>>>> twal...@apache.org > >>>>>>>>>>> : > >>>>>>>>>>> Hi everyone, > >>>>>>>>>>> > >>>>>>>>>>> I would like to continue this discussion thread and convert the > >>>>>> outcome > >>>>>>>>>>> into a FLIP such that users and contributors know what to > expect > >>> in > >>>>>> the > >>>>>>>>>>> upcoming releases. > >>>>>>>>>>> > >>>>>>>>>>> I created a design document [1] that clarifies our motivation > >> why > >>>>> we > >>>>>>>>>>> want to do this, how a Maven module structure could look like, > >> and > >>>>> a > >>>>>>>>>>> suggestion for a migration plan. > >>>>>>>>>>> > >>>>>>>>>>> It would be great to start with the efforts for the 1.8 release > >>>>> such > >>>>>>>>>>> that new features can be developed in Java and major > >> refactorings > >>>>>> such > >>>>>>>>>>> as improvements to the connectors and external catalog support > >> are > >>>>>> not > >>>>>>>>>>> blocked. > >>>>>>>>>>> > >>>>>>>>>>> Please let me know what you think. > >>>>>>>>>>> > >>>>>>>>>>> Regards, > >>>>>>>>>>> Timo > >>>>>>>>>>> > >>>>>>>>>>> [1] > >>>>>>>>>>> > >>>>>>>>>>> > >> > https://docs.google.com/document/d/1PPo6goW7tOwxmpFuvLSjFnx7BF8IVz0w3dcmPPyqvoY/edit?usp=sharing > >>>>>>>>>>> Am 02.07.18 um 17:08 schrieb Fabian Hueske: > >>>>>>>>>>>> Hi Piotr, > >>>>>>>>>>>> > >>>>>>>>>>>> thanks for bumping this thread and thanks for Xingcan for the > >>>>>>>>> comments. > >>>>>>>>>>>> I think the first step would be to separate the flink-table > >>> module > >>>>>>>>> into > >>>>>>>>>>>> multiple sub modules. These could be: > >>>>>>>>>>>> > >>>>>>>>>>>> - flink-table-api: All API facing classes. Can be later > divided > >>>>>>>>> further > >>>>>>>>>>>> into Java/Scala Table API/SQL > >>>>>>>>>>>> - flink-table-planning: involves all planning (basically > >>>>> everything > >>>>>>>>> we > >>>>>>>>>> do > >>>>>>>>>>>> with Calcite) > >>>>>>>>>>>> - flink-table-runtime: the runtime code > >>>>>>>>>>>> > >>>>>>>>>>>> IMO, a realistic mid-term goal is to have the runtime module > >> and > >>>>>>>>>> certain > >>>>>>>>>>>> parts of the planning module ported to Java. > >>>>>>>>>>>> The api module will be much harder to port because of several > >>>>>>>>>>> dependencies > >>>>>>>>>>>> to Scala core classes (the parser framework, tree iterations, > >>>>> etc.). > >>>>>>>>>> I'm > >>>>>>>>>>>> not saying we should not port this to Java, but it is not > clear > >>> to > >>>>>> me > >>>>>>>>>>> (yet) > >>>>>>>>>>>> how to do it. > >>>>>>>>>>>> > >>>>>>>>>>>> I think flink-table-runtime should not be too hard to port. > The > >>>>> code > >>>>>>>>>> does > >>>>>>>>>>>> not make use of many Scala features, i.e., it's writing very > >>>>>>>>> Java-like. > >>>>>>>>>>>> Also, there are not many dependencies and operators can be > >>>>>>>>> individually > >>>>>>>>>>>> ported step-by-step. > >>>>>>>>>>>> For flink-table-planning, we can have certain packages that we > >>>>> port > >>>>>>>>> to > >>>>>>>>>>> Java > >>>>>>>>>>>> like planning rules or plan nodes. The related classes mostly > >>>>> extend > >>>>>>>>>>>> Calcite's Java interfaces/classes and would be natural choices > >>> for > >>>>>>>>>> being > >>>>>>>>>>>> ported. The code generation classes will require more effort > to > >>>>>> port. > >>>>>>>>>>> There > >>>>>>>>>>>> are also some dependencies in planning on the api module that > >> we > >>>>>>>>> would > >>>>>>>>>>> need > >>>>>>>>>>>> to resolve somehow. > >>>>>>>>>>>> > >>>>>>>>>>>> For SQL most work when adding new features is done in the > >>> planning > >>>>>>>>> and > >>>>>>>>>>>> runtime modules. So, this separation should already reduce > >>>>>>>>>> "technological > >>>>>>>>>>>> dept" quite a lot. > >>>>>>>>>>>> The Table API depends much more on Scala than SQL. > >>>>>>>>>>>> > >>>>>>>>>>>> Cheers, Fabian > >>>>>>>>>>>> > >>>>>>>>>>>> > >>>>>>>>>>>> > >>>>>>>>>>>> 2018-07-02 16:26 GMT+02:00 Xingcan Cui <xingc...@gmail.com>: > >>>>>>>>>>>> > >>>>>>>>>>>>> Hi all, > >>>>>>>>>>>>> > >>>>>>>>>>>>> I also think about this problem these days and here are my > >>>>>> thoughts. > >>>>>>>>>>>>> 1) We must admit that it’s really a tough task to > interoperate > >>>>> with > >>>>>>>>>> Java > >>>>>>>>>>>>> and Scala. E.g., they have different collection types (Scala > >>>>>>>>>> collections > >>>>>>>>>>>>> v.s. java.util.*) and in Java, it's hard to implement a > method > >>>>>> which > >>>>>>>>>>> takes > >>>>>>>>>>>>> Scala functions as parameters. Considering the major part of > >> the > >>>>>>>>> code > >>>>>>>>>>> base > >>>>>>>>>>>>> is implemented in Java, +1 for this goal from a long-term > >> view. > >>>>>>>>>>>>> 2) The ideal solution would be to just expose a Scala API and > >>>>> make > >>>>>>>>> all > >>>>>>>>>>> the > >>>>>>>>>>>>> other parts Scala-free. But I am not sure if it could be > >>> achieved > >>>>>>>>> even > >>>>>>>>>>> in a > >>>>>>>>>>>>> long-term. Thus as Timo suggested, keep the Scala codes in > >>>>>>>>>>>>> "flink-table-core" would be a compromise solution. > >>>>>>>>>>>>> > >>>>>>>>>>>>> 3) If the community makes the final decision, maybe any new > >>>>>> features > >>>>>>>>>>>>> should be added in Java (regardless of the modules), in order > >> to > >>>>>>>>>> prevent > >>>>>>>>>>>>> the Scala codes from growing. > >>>>>>>>>>>>> > >>>>>>>>>>>>> Best, > >>>>>>>>>>>>> Xingcan > >>>>>>>>>>>>> > >>>>>>>>>>>>> > >>>>>>>>>>>>>> On Jul 2, 2018, at 9:30 PM, Piotr Nowojski < > >>>>>>>>> pi...@data-artisans.com> > >>>>>>>>>>>>> wrote: > >>>>>>>>>>>>>> Bumping the topic. > >>>>>>>>>>>>>> > >>>>>>>>>>>>>> If we want to do this, the sooner we decide, the less code > we > >>>>> will > >>>>>>>>>> have > >>>>>>>>>>>>> to rewrite. I have some objections/counter proposals to > >> Fabian's > >>>>>>>>>>> proposal > >>>>>>>>>>>>> of doing it module wise and one module at a time. > >>>>>>>>>>>>>> First, I do not see a problem of having java/scala code even > >>>>>> within > >>>>>>>>>> one > >>>>>>>>>>>>> module, especially not if there are clean boundaries. Like we > >>>>> could > >>>>>>>>>> have > >>>>>>>>>>>>> API in Scala and optimizer rules/logical nodes written in > Java > >>> in > >>>>>>>>> the > >>>>>>>>>>> same > >>>>>>>>>>>>> module. However I haven’t previously maintained mixed > >> scala/java > >>>>>>>>> code > >>>>>>>>>>> bases > >>>>>>>>>>>>> before, so I might be missing something here. > >>>>>>>>>>>>>> Secondly this whole migration might and most like will take > >>>>> longer > >>>>>>>>>> then > >>>>>>>>>>>>> expected, so that creates a problem for a new code that we > >> will > >>>>> be > >>>>>>>>>>>>> creating. After making a decision to migrate to Java, almost > >> any > >>>>>> new > >>>>>>>>>>> Scala > >>>>>>>>>>>>> line of code will be immediately a technological debt and we > >>> will > >>>>>>>>> have > >>>>>>>>>>> to > >>>>>>>>>>>>> rewrite it to Java later. > >>>>>>>>>>>>>> Thus I would propose first to state our end goal - modules > >>>>>>>>> structure > >>>>>>>>>>> and > >>>>>>>>>>>>> which parts of modules we want to have eventually Scala-free. > >>>>>>>>> Secondly > >>>>>>>>>>>>> taking all steps necessary that will allow us to write new > >> code > >>>>>>>>>>> complaint > >>>>>>>>>>>>> with our end goal. Only after that we should/could focus on > >>>>>>>>>>> incrementally > >>>>>>>>>>>>> rewriting the old code. Otherwise we could be stuck/blocked > >> for > >>>>>>>>> years > >>>>>>>>>>>>> writing new code in Scala (and increasing technological > debt), > >>>>>>>>> because > >>>>>>>>>>>>> nobody have found a time to rewrite some non important and > not > >>>>>>>>>> actively > >>>>>>>>>>>>> developed part of some module. > >>>>>>>>>>>>>> Piotrek > >>>>>>>>>>>>>> > >>>>>>>>>>>>>>> On 14 Jun 2018, at 15:34, Fabian Hueske <fhue...@gmail.com > > > >>>>>>>>> wrote: > >>>>>>>>>>>>>>> Hi, > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> In general, I think this is a good effort. However, it > won't > >>> be > >>>>>>>>> easy > >>>>>>>>>>>>> and I > >>>>>>>>>>>>>>> think we have to plan this well. > >>>>>>>>>>>>>>> I don't like the idea of having the whole code base > >> fragmented > >>>>>>>>> into > >>>>>>>>>>> Java > >>>>>>>>>>>>>>> and Scala code for too long. > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> I think we should do this one step at a time and focus on > >>>>>>>>> migrating > >>>>>>>>>>> one > >>>>>>>>>>>>>>> module at a time. > >>>>>>>>>>>>>>> IMO, the easiest start would be to port the runtime to > Java. > >>>>>>>>>>>>>>> Extracting the API classes into an own module, porting them > >> to > >>>>>>>>> Java, > >>>>>>>>>>> and > >>>>>>>>>>>>>>> removing the Scala dependency won't be possible without > >>>>> breaking > >>>>>>>>> the > >>>>>>>>>>> API > >>>>>>>>>>>>>>> since a few classes depend on the Scala Table API. > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> Best, Fabian > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> 2018-06-14 10:33 GMT+02:00 Till Rohrmann < > >>> trohrm...@apache.org > >>>>>> : > >>>>>>>>>>>>>>>> I think that is a noble and honorable goal and we should > >>>>> strive > >>>>>>>>> for > >>>>>>>>>>> it. > >>>>>>>>>>>>>>>> This, however, must be an iterative process given the > sheer > >>>>> size > >>>>>>>>> of > >>>>>>>>>>> the > >>>>>>>>>>>>>>>> code base. I like the approach to define common Java > >> modules > >>>>>>>>> which > >>>>>>>>>>> are > >>>>>>>>>>>>> used > >>>>>>>>>>>>>>>> by more specific Scala modules and slowly moving classes > >> from > >>>>>>>>> Scala > >>>>>>>>>>> to > >>>>>>>>>>>>>>>> Java. Thus +1 for the proposal. > >>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>> Cheers, > >>>>>>>>>>>>>>>> Till > >>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>> On Wed, Jun 13, 2018 at 12:01 PM Piotr Nowojski < > >>>>>>>>>>>>> pi...@data-artisans.com> > >>>>>>>>>>>>>>>> wrote: > >>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> Hi, > >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> I do not have an experience with how scala and java > >>> interacts > >>>>>>>>> with > >>>>>>>>>>>>> each > >>>>>>>>>>>>>>>>> other, so I can not fully validate your proposal, but > >>>>> generally > >>>>>>>>>>>>> speaking > >>>>>>>>>>>>>>>> +1 > >>>>>>>>>>>>>>>>> from me. > >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> Does it also mean, that we should slowly migrate > >>>>>>>>>> `flink-table-core` > >>>>>>>>>>> to > >>>>>>>>>>>>>>>>> Java? How would you envision it? It would be nice to be > >> able > >>>>> to > >>>>>>>>>> add > >>>>>>>>>>>>> new > >>>>>>>>>>>>>>>>> classes/features written in Java and so that they can > >>> coexist > >>>>>>>>> with > >>>>>>>>>>> old > >>>>>>>>>>>>>>>>> Scala code until we gradually switch from Scala to Java. > >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> Piotrek > >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>>> On 13 Jun 2018, at 11:32, Timo Walther < > >> twal...@apache.org > >>>>>>>>>> wrote: > >>>>>>>>>>>>>>>>>> Hi everyone, > >>>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>>> as you all know, currently the Table & SQL API is > >>>>> implemented > >>>>>>>>> in > >>>>>>>>>>>>> Scala. > >>>>>>>>>>>>>>>>> This decision was made a long-time ago when the initital > >>> code > >>>>>>>>> base > >>>>>>>>>>> was > >>>>>>>>>>>>>>>>> created as part of a master's thesis. The community kept > >>>>> Scala > >>>>>>>>>>>>> because of > >>>>>>>>>>>>>>>>> the nice language features that enable a fluent Table API > >>>>> like > >>>>>>>>>>>>>>>>> table.select('field.trim()) and because Scala allows for > >>>>> quick > >>>>>>>>>>>>>>>> prototyping > >>>>>>>>>>>>>>>>> (e.g. multi-line comments for code generation). The > >>>>> committers > >>>>>>>>>>>>> enforced > >>>>>>>>>>>>>>>> not > >>>>>>>>>>>>>>>>> splitting the code-base into two programming languages. > >>>>>>>>>>>>>>>>>> However, nowadays the flink-table module more and more > >>>>> becomes > >>>>>>>>> an > >>>>>>>>>>>>>>>>> important part in the Flink ecosystem. Connectors, > >> formats, > >>>>> and > >>>>>>>>>> SQL > >>>>>>>>>>>>>>>> client > >>>>>>>>>>>>>>>>> are actually implemented in Java but need to interoperate > >>>>> with > >>>>>>>>>>>>>>>> flink-table > >>>>>>>>>>>>>>>>> which makes these modules dependent on Scala. As > mentioned > >>> in > >>>>>> an > >>>>>>>>>>>>> earlier > >>>>>>>>>>>>>>>>> mail thread, using Scala for API classes also exposes > >> member > >>>>>>>>>>> variables > >>>>>>>>>>>>>>>> and > >>>>>>>>>>>>>>>>> methods in Java that should not be exposed to users [1]. > >>> Java > >>>>>> is > >>>>>>>>>>> still > >>>>>>>>>>>>>>>> the > >>>>>>>>>>>>>>>>> most important API language and right now we treat it as > a > >>>>>>>>>>>>> second-class > >>>>>>>>>>>>>>>>> citizen. I just noticed that you even need to add Scala > if > >>>>> you > >>>>>>>>>> just > >>>>>>>>>>>>> want > >>>>>>>>>>>>>>>> to > >>>>>>>>>>>>>>>>> implement a ScalarFunction because of method clashes > >> between > >>>>>>>>>> `public > >>>>>>>>>>>>>>>> String > >>>>>>>>>>>>>>>>> toString()` and `public scala.Predef.String toString()`. > >>>>>>>>>>>>>>>>>> Given the size of the current code base, reimplementing > >> the > >>>>>>>>>> entire > >>>>>>>>>>>>>>>>> flink-table code in Java is a goal that we might never > >>> reach. > >>>>>>>>>>>>> However, we > >>>>>>>>>>>>>>>>> should at least treat the symptoms and have this as a > >>>>> long-term > >>>>>>>>>> goal > >>>>>>>>>>>>> in > >>>>>>>>>>>>>>>>> mind. My suggestion would be to convert user-facing and > >>>>> runtime > >>>>>>>>>>>>> classes > >>>>>>>>>>>>>>>> and > >>>>>>>>>>>>>>>>> split the code base into multiple modules: > >>>>>>>>>>>>>>>>>>> flink-table-java {depends on flink-table-core} > >>>>>>>>>>>>>>>>>> Implemented in Java. Java users can use this. This would > >>>>>>>>> require > >>>>>>>>>> to > >>>>>>>>>>>>>>>>> convert classes like TableEnvironment, Table. > >>>>>>>>>>>>>>>>>>> flink-table-scala {depends on flink-table-core} > >>>>>>>>>>>>>>>>>> Implemented in Scala. Scala users can use this. > >>>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>>>> flink-table-common > >>>>>>>>>>>>>>>>>> Implemented in Java. Connectors, formats, and UDFs can > >> use > >>>>>>>>> this. > >>>>>>>>>> It > >>>>>>>>>>>>>>>>> contains interface classes such as descriptors, table > >> sink, > >>>>>>>>> table > >>>>>>>>>>>>> source. > >>>>>>>>>>>>>>>>>>> flink-table-core {depends on flink-table-common and > >>>>>>>>>>>>>>>>> flink-table-runtime} > >>>>>>>>>>>>>>>>>> Implemented in Scala. Contains the current main code > >> base. > >>>>>>>>>>>>>>>>>>> flink-table-runtime > >>>>>>>>>>>>>>>>>> Implemented in Java. This would require to convert > >> classes > >>>>> in > >>>>>>>>>>>>>>>>> o.a.f.table.runtime but would improve the runtime > >>>>> potentially. > >>>>>>>>>>>>>>>>>> What do you think? > >>>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>>> Regards, > >>>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>>> Timo > >>>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>>> [1] > >>>>>>>>>>>>>>>>> http://apache-flink-mailing-list-archive.1008284.n3. > >>>>>>>>>>>>>>>> nabble.com/DISCUSS-Convert-main-Table-API-classes-into- > >>>>>>>>>>>>> traits-tp21335.html > >>> > >
