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From Till Rohrmann <trohrm...@apache.org>
Subject Re: [DISCUSS] Changing Flink's shading model
Date Thu, 11 May 2017 08:59:23 GMT
I agree that shading is a nasty business it would make things a bit more
explicit to program directly against the relocated API of the
above-mentioned libraries. I assume that we should be able to follow the
examples of flakka and frocks. Have we somewhere documented how to publish
artifacts on Maven central?

On Thu, May 11, 2017 at 10:54 AM, Stephan Ewen <sewen@apache.org> wrote:

> @Ufuk  - I have never set up artifact deployment in Maven, could need some
> help there.
>
> Regarding shading Netty, I agree, would be good to do that as well...
>
> On Thu, May 11, 2017 at 10:52 AM, Ufuk Celebi <uce@apache.org> wrote:
>
> > The advantages you've listed sound really compelling to me.
> >
> > - Do you have time to implement these changes or do we need a volunteer?
> ;)
> >
> > - I assume that republishing the artifacts as you propose doesn't have
> > any new legal implications since we already publish them with our
> > JARs, right?
> >
> > - We might think about adding Netty to the list of shaded artifacts
> > since some dependency conflicts were reported recently. Would have to
> > double check the reported issues before doing that though. ;-)
> >
> > – Ufuk
> >
> >
> > On Wed, May 10, 2017 at 8:45 PM, Stephan Ewen <sewen@apache.org> wrote:
> > > @chesnay: I used ASM as an example in the proposal. Maybe I did not say
> > > that clearly.
> > >
> > > If we like that approach, we should deal with the other libraries (at
> > least
> > > the frequently used ones) in the same way.
> > >
> > >
> > > I would imagine to have a project layout like that:
> > >
> > > flink-shaded-deps
> > >   - flink-shaded-asm
> > >   - flink-shaded-guava
> > >   - flink-shaded-curator
> > >   - flink-shaded-hadoop
> > >
> > >
> > > "flink-shaded-deps" would not be built every time (and not be released
> > > every time), but only when needed.
> > >
> > >
> > >
> > >
> > >
> > >
> > > On Wed, May 10, 2017 at 7:28 PM, Chesnay Schepler <chesnay@apache.org>
> > > wrote:
> > >
> > >> I like the idea, thank you for bringing it up.
> > >>
> > >> Given that the raised problems aren't really ASM specific would it
> make
> > >> sense to create one flink-shaded module that contains all frequently
> > shaded
> > >> libraries? (or maybe even all shaded dependencies by core modules) The
> > >> proposal limits the scope of this to ASM and i was wondering why.
> > >>
> > >> I also remember that there was a discussion recently about why we
> shade
> > >> things at all, and the idea of working against the shaded namespaces
> was
> > >> brought up. Back then i was expressing doubts as to whether IDE's
> would
> > >> properly support this; what's the state on that?
> > >>
> > >> On 10.05.2017 18:18, Stephan Ewen wrote:
> > >>
> > >>> Hi!
> > >>>
> > >>> This is a discussion about altering the way we handle dependencies
> and
> > >>> shading in Flink.
> > >>> I ran into quite a view problems trying to adjust / fix some shading
> > >>> issues
> > >>> during release validation.
> > >>>
> > >>> The issue is tracked under: https://issues.apache.org/jira
> > >>> /browse/FLINK-6529
> > >>> Bring this discussion thread up because it is a bigger issue
> > >>>
> > >>> *Problem*
> > >>>
> > >>> Currently, Flink shades dependencies like ASM and Guava into all jars
> > of
> > >>> projects that reference it and relocate the classes.
> > >>>
> > >>> There are some drawbacks to that approach, let's discuss them at the
> > >>> example of ASM:
> > >>>
> > >>>    - The ASM classes are for example in flink-core, flink-java,
> > >>> flink-scala,
> > >>> flink-runtime, etc.
> > >>>
> > >>>    - Users that reference these dependencies have the classes
> multiple
> > >>> times
> > >>> in the classpath. That is unclean (works, through, because the
> classes
> > are
> > >>> identical). The same happens when building the final dist. jar.
> > >>>
> > >>>    - Some of these dependencies require to include license files in
> the
> > >>> shaded jar. It is hard to impossible to build a good automatic
> solution
> > >>> for
> > >>> that, partly due to Maven's very poor cross-project path support
> > >>>
> > >>>    - Most importantly: Scala does not support shading really well.
> > Scala
> > >>> classes have references to classes in more places than just the class
> > >>> names
> > >>> (apparently for Scala reflect support). Referencing a Scala project
> > with
> > >>> shaded ASM still requires to add a reference to unshaded ASM (at
> least
> > as
> > >>> a
> > >>> compile dependency).
> > >>>
> > >>> *Proposal*
> > >>>
> > >>> I propose that we build and deploy a asm-flink-shaded version of ASM
> > and
> > >>> directly program against the relocated namespaces. Since we never use
> > >>> classes that we relocate in public interfaces, Flink users will never
> > see
> > >>> the relocated class names. Internally, it does not hurt to use them.
> > >>>
> > >>>    - Proper maven dependency management, no hidden (shaded)
> > dependencies
> > >>>
> > >>>    - One copy of each class for shaded dependencies
> > >>>
> > >>>    - Proper Scala interoperability
> > >>>
> > >>>    - Natural License management (license is part of deployed
> > >>> asm-flink-shaded jar)
> > >>>
> > >>>
> > >>> Happy to hear thoughts!
> > >>>
> > >>> Stephan
> > >>>
> > >>>
> > >>
> >
>

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