Thanks Becket for your reply! *On Option 1:* - I personally consider API inconsistencies more important, since they will remain with us "forever", but this is up to the community. I can implement whichever solution we decide upon.
*Option 2:* - I don't think this specific issue merits a rewrite, but if we decide to change our approach, then it's a different story. *Evolvability:* This discussion reminds me of a similar discussion on FLIP-372 [1], where we are trying to decide if we should use mixin interfaces, or use interface inheritance. With the mixin approach, we have a more flexible interface, but we can't check the generic types of the interfaces/classes on compile time, or even when we create the DAG. The first issue happens when we call the method and fail. The issue here is similar: - *StatefulSink* needs a writer with a method to `*snapshotState*` - *TwoPhaseCommittingSink* needs a writer with `*prepareCommit*` - If there is a Sink which is stateful and needs to commit, then it needs both of these methods. If we use the mixin solution here, we lose the possibility to check the types in compile time. We could do the type check in runtime using ` *instanceof*`, so we are better off than with the FLIP-372 example above, but still lose any important possibility. I personally prefer the mixin approach, but that would mean we rewrite the Sink API again - likely a SinkV3. Are we ready to move down that path? Thanks, Peter [1] - https://lists.apache.org/thread/344pzbrqbbb4w0sfj67km25msp7hxlyd On Thu, Nov 30, 2023, 14:53 Becket Qin <becket....@gmail.com> wrote: > Hi folks, > > Sorry for replying late on the thread. > > For this particular FLIP, I see two solutions: > > Option 1: > 1. On top of the the current status, rename > *org.apache.flink.api.connector.sink2.InitContext *to > *CommonInitContext (*should > probably be package private*)*. > 2. Change the name *WriterInitContext* back to *InitContext, *and revert > the deprecation. We can change the parameter name to writerContext if we > want to. > Admittedly, this does not have full symmetric naming of the InitContexts - > we will have CommonInitContext / InitContext / CommitterInitContext instead > of InitContext / WriterInitContext / CommitterInitContext. However, the > naming seems clear without much confusion. Personally, I can live with > that, treating the class InitContext as a non-ideal legacy class name > without much material harm. > > Option 2: > Theoretically speaking, if we really want to reach the perfect state while > being backwards compatible, we can create a brand new set of Sink > interfaces and deprecate the old ones. But I feel this is an overkill here. > > The solution to this particular issue aside, the evolvability of the > current interface hierarchy seems a more fundamental issue and worries me > more. I haven't completely thought it through, but there are two noticeable > differences between the interface design principles between Source and > Sink. > 1. Source uses decorative interfaces. For example, we have a > SupportsFilterPushdown interface, instead of a subclass of > FilterableSource. This seems provides better flexibility. > 2. Source tends to have a more coarse-grained interface. For example, > SourceReader always has the methods of snapshotState(), > notifyCheckpointComplete(). Even if they may not be always required, we do > not separate them into different interfaces. > My hunch is that if we follow similar approach as Source, the evolvability > might be better. If we want to do this, we'd better to do it before 2.0. > What do you think? > > Process wise, > - I agree that if there is a change to the passed FLIP during > implementation, it should be brought back to the mailing list. > - There might be value for the connector nightly build to depend on the > latest snapshot of the same Flink major version. It helps catching > unexpected breaking changes sooner. > - I'll update the website to reflect the latest API stability policy. > Apologies for the confusion caused by the stale doc. > > Thanks, > > Jiangjie (Becket) Qin > > > > On Wed, Nov 29, 2023 at 10:55 PM Márton Balassi <balassi.mar...@gmail.com> > wrote: > > > Thanks, Martijn and Peter. > > > > In terms of the concrete issue: > > > > - I am following up with the author of FLIP-321 [1] (Becket) to update > > the docs [2] to reflect the right state. > > - I see two reasonable approaches in terms of proceeding with the > > specific changeset: > > > > > > 1. We allow the exception from FLIP-321 for this change and let the > > PublicEvolving API change happen between Flink 1.18 and 1.19, which > > is > > consistent with current state of the relevant documentation. [2] > > We commit > > to helping the connector repos make the necessary (one liner) > > changes. > > 2. We revert back to the original implementation plan as explicitly > > voted on in FLIP-371 [3]. That has no API breaking changes. > > However we end > > up with an inconsistently named API with duplicated internal > > methods. Peter > > has also discovered additional bad patterns during his work in > > FLIP-372 > > [3], the total of these changes could be handled in a separate FLIP > > that > > would do multiple PublicEvolving breaking changes to clean up the > > API. > > > > In terms of the general issues: > > > > - I agree that if a PR review of an accepted FLIP newly introduces a > > breaking API change that warrants an update to the mailing list > > discussion > > and possibly even a new vote. > > - I agree with the general sentiment of FLIP-321 to provide stronger > API > > guarantees with the minor note that if we have changes in mind we > should > > prioritize them now such that they can be validated by Flink 2.0. > > - I agree that ideally the connector repos should build against the > > latest release and not the master branch. > > > > [1] > > > > > https://cwiki.apache.org/confluence/display/FLINK/FLIP-321%3A+Introduce+an+API+deprecation+process > > [2] > > > > > https://nightlies.apache.org/flink/flink-docs-master/docs/ops/upgrading/#api-compatibility-guarantees > > [3] > > > > > https://cwiki.apache.org/confluence/display/FLINK/FLIP-371%3A+Provide+initialization+context+for+Committer+creation+in+TwoPhaseCommittingSink > > [4] > > > > > https://cwiki.apache.org/confluence/display/FLINK/FLIP-372%3A+Allow+TwoPhaseCommittingSink+WithPreCommitTopology+to+alter+the+type+of+the+Committable > > > > Best, > > Marton > > > > On Mon, Nov 27, 2023 at 7:23 PM Péter Váry <peter.vary.apa...@gmail.com> > > wrote: > > > > > I think we should try to separate the discussion in a few different > > topics: > > > > > > - Concrete issue > > > - How to solve this problem in 1.19 and wrt the affected > > createWriter > > > interface > > > - Update the documentation [1], so FLIP-321 is visible for every > > > contributor > > > - Generic issue > > > - API stability > > > - Connector dependencies > > > > > > > > > *CreateWriter interface* > > > The change on the createWriter is not strictly required for the > > > functionality defined by the requirements on the FLIP. > > > If the only goal is only to have a backward compatible API, we can > simply > > > create a separate `*CommitterInitContext*` object and do not touch the > > > writer `*InitContext*`, like it was done in the original PR [2]. > > > The issue is that this would result in an implementation which has > > > duplicated methods/implementations (internal issue only), and has > > > inconsistent naming (issue for external users). > > > > > > If we want to create an API which is consistent (and I agree with the > > > reviewer's comments), then we need to rename the parameter type ( > > > *WriterInitContext*) for the createWriter method. > > > I have tried to keep the backward compatibility with creating a new > > method > > > and providing a default implementation for this new method which would > > call > > > the original method after converting the WriterInitContext to > > InitContext. > > > > > > This is failed because the following details: > > > > > > - *org.apache.flink.api.connector.sink2.Sink* defines > > > `*SinkWriter<InputT> > > > createWriter(InitContext context)`* > > > - *org.apache.flink.api.connector.sink2.StatefulSink* narrows it > > > down to *`StatefulSinkWriter<InputT, > > > WriterStateT> createWriter(InitContext context)`* > > > - *org.apache.flink.api.connector.sink2.TwoPhaseCommittingSink* > > narrows > > > it down to *`PrecommittingSinkWriter<InputT, CommT> > > > createWriter(WriterInitContext context)`* > > > - > > > > > > > > > *org.apache.flink.streaming.runtime.operators.sink.TestSinkV2.TestStatefulSinkV2* > > > implements *StatefulSink* and *TwoPhaseCommittingSink* too > > > > > > *TestStatefulSinkV2* is a good example where we can not achieve > backward > > > compatibility, since the the compiler will fail with unrelated default > > > methods [3] > > > > > > I am open for any suggestions how to move to the new API, and keep the > > > backward compatibility. If we do not find a way to keep backward > > > compatibility, and we decide that we would like to honour FLIP-321, > then > > we > > > can reverting to the original solution and keep only the changes for > the > > ` > > > *createCommitter*` method. > > > > > > *Update the documentation* > > > I have not found only one place in the docs [1], where we talk about > the > > > compatibility guarantees. > > > Based FLIP-321 and the result of the discussion here, we should update > > this > > > page. > > > > > > *API stability* > > > I agree with the general sentiment of FLIP-321 to keep the changes > > backward > > > compatible as much as possible. But the issue above highlights that > there > > > could be situations where it is not possible to achieve backward > > > compatibility. Probably we should provide exceptions to handle this > kind > > of > > > situations - minimally for PublicEvolving interfaces. After we agree on > > > long term goals - allowing exceptions or to be more lenient on backward > > > compatibility guarantees, or sticking to FLIP-321 by the letter - we > > could > > > discuss how to apply it to the current situation. > > > > > > *Connector dependencies* > > > I think it is generally a good practice to depend on the stable version > > of > > > Flink (or any other downstream project). This is how we do it in > Iceberg, > > > and how it was implemented in the Kafka connector as well. This would > > > result in more stable connector builds. The only issue I see, that the > > > situations like this would take longer to surface, but I fully expect > us > > to > > > get better at compatibility after we wetted the process. > > > > > > [1] - > > > > > > > > > https://nightlies.apache.org/flink/flink-docs-master/docs/ops/upgrading/#api-compatibility-guarantees > > > [2] - > > > > > > > > > https://github.com/apache/flink/pull/23555/commits/2b9adeb20e55c33a623115efa97d3149c11e9ca4 > > > [3] - > https://github.com/apache/flink/pull/23555#discussion_r1371740397 > > > > > > Martijn Visser <martijnvis...@apache.org> ezt írta (időpont: 2023. > nov. > > > 27., H, 11:21): > > > > > > > Hi all, > > > > > > > > I'm opening this discussion thread to bring a discussion that's > > > > happening on a completed Jira ticket back to the mailing list [1] > > > > > > > > In summary: > > > > > > > > * There was a discussion and a vote on FLIP-371 [2] > > > > * During implementation, it was determined that there's a diamond > > > > inheritance problem on the Sink.createWriter method, making a > > > > backwards compatible change hard/impossible (I think this is where > the > > > > main discussion point actually is) [3] > > > > * The PR was merged, causing a backwards incompatible change without > a > > > > discussion on the Dev mailing list > > > > > > > > I think that in hindsight, even though there was a FLIP on this > topic, > > > > the finding of the diamond inheritance issue should have been brought > > > > back to the Dev mailing list in order to agree on how to resolve it. > > > > Since 1.19 is still under way, we still have time to fix this. > > > > > > > > I think there's two things we can improve: > > > > > > > > 1) Next time during implementation of a FLIP/PR which involves a > > > > non-backward compatible change of an API that wasn't accounted for, > > > > the discussion should be brought back to the Dev mailing list. I > think > > > > we can just add that to the FLIP bylaws. > > > > 2) How do we actually resolve the problem: is there anyone who has an > > > > idea on how we could introduce the proposed change while maintaining > > > > backwards compatibility, or do we agree that while this is an non > > > > desired situation, there is no better alternative unfortunately? > > > > > > > > Best regards, > > > > > > > > Martijn > > > > > > > > [1] https://issues.apache.org/jira/browse/FLINK-25857 > > > > [2] > > > > > > > > > > https://cwiki.apache.org/confluence/display/FLINK/FLIP-371%3A+Provide+initialization+context+for+Committer+creation+in+TwoPhaseCommittingSink > > > > [3] > https://github.com/apache/flink/pull/23555#discussion_r1371740397 > > > > > > > > > >
