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From Ufuk Celebi <...@apache.org>
Subject Re: Replacing JobManager with Scala implementation
Date Thu, 04 Sep 2014 22:38:44 GMT
Hey Daniel,

On Thu, Sep 4, 2014 at 11:36 PM, Daniel Warneke <warneke@apache.org> wrote:

> I agree that the questions “akka” and “Scala” should be treated
> separately. Unfortunately, this is not how the discussion has been led so
> far. Instead, the new akka RPC service is used to motivate the necessity
> for Scala in the runtime core. I still don’t see that necessity. I tried to
> find the implementation of the new akka RPC service on github. The only
> code I found was from Asterios, but it looks like he was perfectly able to
> encapsulate the whole akka RPC thing in 5 Java classes [1].
>

I don't think that anybody is talking about the necessity of Scala. Yes,
Akka and an actor based refactoring of core runtime parts result in a hard
dependency to Scala for the core (because Akka is written in Scala), but it
does *not* necessitate to do the refactoring itself in Scala, because there
is an Akka Java API as well.

Are you concerned with the dependency to Scala or with using Akka's Scala
API?

I think that Till started this thread and the [VOTE] exactly because he is
well aware that it is *not* necessary to do it in Scala. He sees good
reasons to do it in Scala and asks the community to vote on it. Again,
because he is aware that this is not a small or light weight change.

The second argument (Scala will attract new developers to the project) is
> nothing but speculation. This might as well totally backfire and lead to
> the opposite.
>

I agree that this point is speculative and both outlined outcomes (attract
or repel developers) are possible. But it is also not the only argument
that has been raised in favor of Scala. Other more technical (not
speculative) points have been given. It is the goal of the vote to find a
consensus about whether these points are sufficient or not.


> The only explanation I have for this push towards akka and Scala is that
> there are already plans to expand the usage of akka way beyond pure RPC. In
> this case, I feel these plans should be clearly articulated on the dev
> list. A simple RPC service does not justify the proposed changes in my
> opinion.
>

There is no push for Scala. It's a vote. And the reasons for going for Akka
have been repeated a few times by now.

I think the way that Asterios initially introduced Akka beneath the
existing RPC proxy service (independently of whether he did in Scala or
Java) would not allow us to make use of central features of Akka (some of
which Till and Stephan outlined).

Best wishes,

Ufuk

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