flink-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Stephan Ewen <se...@apache.org>
Subject Re: [DISCUSS] Backwards compatibility policy.
Date Tue, 27 Jun 2017 16:03:49 GMT
I think that this discussion is probably motivated especially by the
"legacy state" handling of Flink 1.1.
The biggest gain in codebase and productivity would be won only by dropping
1.1 compatibility in Flink 1.4.

My gut feeling is that this is reasonable. We support two versions back,
which means that users can skip one upgrade, but not two.

>From what I can tell, users are usually eager to upgrade. They don't do it
immediately, but as soon as the new release is a bit battle tested.

I would expect skipping two entire versions to be rare enough to be okay
with a solution which is a bit more effort for the user:
You can upgrade from Flink 1.1. to 1.4 by loading the 1.1 savepoint into
Flink 1.2, take a savepoint (1.2 format), and resume that in Flink 1.4.

Greetings,
Stephan


On Tue, Jun 27, 2017 at 12:01 PM, Stefan Richter <
s.richter@data-artisans.com> wrote:

> For many parts of the code, I would agree with Aljoscha. However, I can
> also see notable exceptions, such as maintaining support for the legacy
> state from Flink <=1.1. For example, I think dropping support for this can
> simplify new developments such as fast local recovery or state replication
> quiet a bit because this is a special case that runs through a lot of code
> from backend to JM. So besides this general discussion about a backwards
> compatible policy, do you think it could make sense to start another
> concrete discussion about if we still must or want backwards compatibility
> to Flink 1.1 in Flink 1.4?
>
> > Am 29.05.2017 um 12:08 schrieb Aljoscha Krettek <aljoscha@apache.org>:
> >
> > Normally, I’m the first one to suggest removing everything that is not
> absolutely necessary in order to have a clean code base. On this issue,
> though, I think we should support restoring from old Savepoints as far back
> as possible if it does not make the code completely unmaintainable. Some
> users might jump versions and always forcing them to go though every
> version from their old version to the current version doesn’t seem feasible
> and might put off some users.
> >
> > So far, I think the burden of supporting restore from 1.1 is still small
> enough and with each new version the changes between versions become less
> and less. The changes from 1.2 to the upcoming 1.3 are quite minimal, I
> think.
> >
> > Best,
> > Aljoscha
> >> On 24. May 2017, at 17:58, Ted Yu <yuzhihong@gmail.com> wrote:
> >>
> >> bq. about having LTS versions once a year
> >>
> >> +1 to the above.
> >>
> >> There may be various reasons users don't want to upgrade (after new
> >> releases come out). We should give such users enough flexibility on the
> >> upgrade path.
> >>
> >> Cheers
> >>
> >> On Wed, May 24, 2017 at 8:39 AM, Kostas Kloudas <
> k.kloudas@data-artisans.com
> >>> wrote:
> >>
> >>> Hi all,
> >>>
> >>> For the proposal of having a third party tool, I agree with Ted.
> >>> Maintaining
> >>> it is a big and far from trivial effort.
> >>>
> >>> Now for the window of backwards compatibility, I would argue that even
> if
> >>> for some users 4 months (1 release) is not enough to bump their Flink
> >>> version,
> >>> the proposed policy guarantees that there will always be a path from
> any
> >>> old
> >>> version to any subsequent one.
> >>>
> >>> Finally, for the proposal about having LTS versions once a year, I am
> not
> >>> sure if this will reduce or create more overhead. If I understand the
> plan
> >>> correctly, this would mean that the community will have to maintain
> >>> 2 or 3 LTS versions and the last two major ones, right?
> >>>
> >>>> On May 22, 2017, at 7:31 PM, Ted Yu <yuzhihong@gmail.com> wrote:
> >>>>
> >>>> For #2, it is difficult to achieve:
> >>>>
> >>>> a. maintaining savepoint migration is non-trivial and should be
> reviewed
> >>> by
> >>>> domain experts
> >>>> b. how to certify such third-party tool
> >>>>
> >>>> Cheers
> >>>>
> >>>> On Mon, May 22, 2017 at 3:04 AM, 施晓罡 <shixiaogangg@gmail.com>
wrote:
> >>>>
> >>>>> Hi all,
> >>>>>
> >>>>> Currently, we work a lot in the maintenance of compatibility.
> >>>>> There exist much code in runtime to support the migration of
> savepoints
> >>>>> (most of which are deprecated), making it hard to focus on the
> current
> >>>>> implementation.
> >>>>> When more versions are released, much more efforts will be needed
if
> we
> >>>>> try to make these released versions compatible.
> >>>>>
> >>>>> I agree with Tzu-Li that we should provide a method to let users
> upgrade
> >>>>> Flink in a reasonable pace.
> >>>>> But i am against the proposal that we only offer backwards
> compatibility
> >>>>> for one previous version.
> >>>>> According our time-based release model, a major version is released
> >>> every
> >>>>> four month.
> >>>>> That means, users have to upgrade their versions every 8 months.
> >>> Otherwise
> >>>>> they will have difficulties in the migration of existing savepoints.
> >>>>>
> >>>>> My suggestions include
> >>>>>
> >>>>> (1) We can release Long-Term Support (LTS) versions which are widely
> >>>>> adopted in other open-source projects.
> >>>>> LTS versions should be stable and are free of found bugs. Savepoints
> in
> >>>>> LTS versions are guaranteed to be back-compatible so that users
can
> >>> easily
> >>>>> upgrade to newer LTS versions.
> >>>>>
> >>>>> The releasing of LTS versions is slower than that of major versions
> >>> (maybe
> >>>>> once a year, determined by users’ upgrade frequency).
> >>>>> Each LTS version will be supported a period of time and typically
> there
> >>>>> are no more than three active LTS versions.
> >>>>> By encouraging users to use LTS versions, we can ease the
> maintenance of
> >>>>> released versions (bug fixes, back compatibility, and critical
> >>> performance
> >>>>> improvement).
> >>>>>
> >>>>> (2) We can provide a third-party tool to do the migration of
> >>> old-versioned
> >>>>> savepoints.
> >>>>> When users upgrade their versions, they can use the provided tool
to
> >>>>> migrate existing savepoints.
> >>>>> This can help move the code for savepoint migration out of the actual
> >>>>> codebase,  making code focuses on current implementation.
> >>>>>
> >>>>> What do you think?
> >>>>>
> >>>>> Regards,
> >>>>> Xiaogang
> >>>>>
> >>>>>
> >>>>>> 在 2017年5月22日,下午1:39,Tzu-Li (Gordon) Tai <tzulitai@apache.org>
写道:
> >>>>>>
> >>>>>> Hi Kostas,
> >>>>>>
> >>>>>> Thanks for bringing this up!
> >>>>>> I think it is reasonable to keep this coherent with our timely-based
> >>>>> release model guarantees.
> >>>>>>
> >>>>>> With the timely-based release model, there is a guarantee that
the
> >>>>> current latest major version and the previous one is supported.
> >>>>>> For example, upon releasing 1.3, only 1.3 and 1.2 will still
be
> >>>>> supported by the community for any required bug fixes.
> >>>>>> I think this was initially decided not only to ease old version
> >>>>> maintenance efforts for the community, but also as a means to let
> users
> >>>>> upgrade their Flink versions in a reasonable pace (at least every
> other
> >>>>> major release.)
> >>>>>>
> >>>>>> Therefore, I think its also reasonable to also clearly state
that
> >>>>> savepoints compatibility will only be guaranteed for the previous
> >>> release.
> >>>>>> Although I think at the moment almost, if not all, of the current
> code
> >>>>> still maintains compatibility for 1.1, in the long run these
> migration
> >>>>> codes would definitely start to pile up and pollute the actual
> codebase
> >>> if
> >>>>> we try to always be compatible with all previous versions.
> >>>>>>
> >>>>>> Cheers,
> >>>>>> Gordon
> >>>>>>
> >>>>>>
> >>>>>> On 21 May 2017 at 2:24:53 AM, Kostas Kloudas (
> >>>>> k.kloudas@data-artisans.com) wrote:
> >>>>>>
> >>>>>> Hi Chesnay,
> >>>>>>
> >>>>>> I believe that for APIs we already have a pretty clear policy
with
> the
> >>>>> annotations.
> >>>>>> I was referring to savepoints and state related backwards
> >>> compatibility.
> >>>>>>
> >>>>>>
> >>>>>>> On May 20, 2017, at 7:20 PM, Chesnay Schepler <chesnay@apache.org>
> >>>>> wrote:
> >>>>>>>
> >>>>>>> I think it would be a good to clarify what kind of
> >>>>> backwards-compatibilitiy we're talking about here. As in are we
> talking
> >>>>> about APIs or savepoints?
> >>>>>>>
> >>>>>>> On 20.05.2017 19:09, Kostas Kloudas wrote:
> >>>>>>>> Hi all,
> >>>>>>>>
> >>>>>>>> As we are getting closer to releasing Flink-1.3, I would
like to
> open
> >>>>> a discussion
> >>>>>>>> on how far back we provide backwards compatibility for.
> >>>>>>>>
> >>>>>>>> The reason for opening the discussion is that i) for
the users and
> >>> for
> >>>>> the
> >>>>>>>> adoption of the project, it is good to have an explicitely
stated
> >>>>> policy that implies
> >>>>>>>> certain guarantees, and ii) keeping code and tests for
backwards
> >>>>> compatibility with
> >>>>>>>> Flink-1.1 does not offer much. On the contrary, I think
that it
> leads
> >>>>> to:
> >>>>>>>>
> >>>>>>>> 1) dead or ugly code in the codebase, e.g. deprecated
class fields
> >>>>> that could go away and
> >>>>>>>> ugly if() loops (see aligned window operators that were
> deprecated in
> >>>>> 1.2 and are now
> >>>>>>>> normal windows), etc
> >>>>>>>> 2) expensive tests (as, normally, they read from a savepoint)
> >>>>>>>> 3) binary files in the codebase for holding the aforementioned
> >>>>> savepoints
> >>>>>>>>
> >>>>>>>> My proposal for such a policy would be to offer backwards
> >>>>> compatibility for one previous version.
> >>>>>>>>
> >>>>>>>> This means that 1.3 will be compatible with 1.2 (not
1.1). This
> still
> >>>>> allows a clear
> >>>>>>>> "backwards compatibility" path when jumping versions
(a user that
> >>> goes
> >>>>>>>> from 1.1 to 1.3 can go initially 1.1 -> 1.2, take
a savepoint, and
> >>>>> then 1.2 -> 1.3),
> >>>>>>>> while also allowing us to clean up the codebase a bit.
> >>>>>>>>
> >>>>>>>> What do you think?
> >>>>>>>>
> >>>>>>>> Kostas
> >>>>>>>
> >>>>>>>
> >>>>>>
> >>>>>
> >>>>>
> >>>
> >>>
> >
>
>

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message