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From Stefan Richter <s.rich...@data-artisans.com>
Subject Re: [DISCUSS] Backwards compatibility policy.
Date Tue, 27 Jun 2017 10:01:43 GMT
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>
>>>>> 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
>>>>> 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
>>>>> 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
>>>>> 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>
>>>>>> 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
>>>>> 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
>>>>> 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
>>>>> 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
>>>>> that could go away and
>>>>>>>> ugly if() loops (see aligned window operators that were deprecated
>>>>> 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
>>> goes
>>>>>>>> from 1.1 to 1.3 can go initially 1.1 -> 1.2, take a savepoint,
>>>>> then 1.2 -> 1.3),
>>>>>>>> while also allowing us to clean up the codebase a bit.
>>>>>>>> What do you think?
>>>>>>>> Kostas

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