@Kurt: Yes, I don't think that that forks of Flink will have a hard time
to keep up with the porting. That is also why I called this `long-term
goal` because I don't see big resources for the porting to happen
quicker. But at least new features, API, and runtime profit from Java to
Scala conversion.
@Jark: I updated the document:
1. flink-table-common has been renamed to flink-table-spi by request.
2. Yes, good point. flink-sql-client can be moved there as well.
3. I added a paragraph to the document. Porting the code generation to
Java makes only sense if acceptable tooling for it is in place.
Thanks for the feedback,
Timo
Am 29.11.18 um 08:28 schrieb Jark Wu:
Hi Timo,
Thanks for the great work!
Moving flink-table to Java is a long-awaited things but will involve much
effort. Agree with that we should make it as a long-term goal.
I have read the google doc and +1 for the proposal. Here I have some
questions:
1. Where should the flink-table-common module place ? Will we move the
flink-table-common classes to the new modules?
2. Should flink-sql-client also as a sub-module under flink-table ?
3. The flink-table-planner contains code generation and will be converted
to Java. Actually, I prefer using Scala to code generate because of the
Multiline-String and String-Interpolation (i.e. s"hello $user") features in
Scala. It makes code of code-generation more readable. Do we really
want to migrate
code generation to Java?
Best,
Jark
On Wed, 28 Nov 2018 at 09:14, Kurt Young <ykt...@gmail.com> wrote:
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
