I think we should try to sort this out because it might affect how and when finish() will be called (or in general how the operator lifecycle looks like).
To give an example let's take a look at the stop-with-savepoint w/ and w/o --drain: 1) stop-with-savepoint w/o --drain: Conceptually what we would like to do is to stop processing w/o completing any windows or waiting for the AsyncOperator to finish its operations. All these unfinished operations should become part of the final checkpoint so that we can resume from it at a later point. Depending on what finish() does (flush unfinished windows or not), this method must or must not be called. Assuming that finish() flushes unfinished windows/waits for uncompleted async operations, we clearly shouldn't call it. But then there is the question, how do we signal the operator that the next checkpoint is supposed to stop the operator (how will the operator's lifecycle look in this case)? Maybe we simply don't tell the operator and handle this situation on the StreamTask level. If finish() does not flush unfinished windows, then it shouldn't be a problem. 2) stop-with-savepoint w/ --drain: Here we want to complete all pending operations and flush out all results because we don't intend to resume the job. Conceptually, we tell the system that we have reached MAX_WATERMARK. If finish() is defined so that it implicitly advances the watermark to MAX_WATERMARK, then there is no problem. If finish() does not have this semantic, then we need to send the MAX_WATERMARK before sending the endOfInput event to a downstream task. In fact, stop-with-savepoint /w --drain shouldn't be a lot different from a bounded source that reaches its end. It would also send MAX_WATERMARK and then signal the endOfInput event (note that endOfInput is decoupled from the event time here). So I guess the question is will finish() advance the time to the end or is this a separate mechanism (e.g. explicit watermarks). Concerning how to handle processing time, I am a bit unsure tbh. I can see arguments for completing processing time windows/firing processing time timers when calling stop-with-savepoint w/ --drain. On the other hand, I could also see that people want to define actions based on the wall clock time that are independent of the stream state and, thus, would want to ignore them if the Flink application is stopped before reaching this time. Cheers, Till On Fri, Jul 16, 2021 at 7:48 AM Piotr Nowojski <pnowoj...@apache.org> wrote: > Hi Till, > > > 1) Does endOfInput entail sending of the MAX_WATERMARK? > > > > 2) StreamOperator.finish says to flush all buffered events. Would a > > WindowOperator close all windows and emit the results upon calling > > finish, for example? > > 1) currently they are independent but parallel mechanisms. With event time, > they are basically the same. > 2) it probably should for the sake of processing time windows. > > Here you are touching the bit of the current design that I like the least. > We basically have now three different ways of conveying very similar > things: > a) sending `MAX_WATERMARK`, used by event time WindowOperator (what about > processing time?) > b) endInput(), used for example by AsyncWaitOperator to flush it's internal > state > c) finish(), used for example by ContinuousFileReaderOperator > > It's a bit messy and I'm not sure if this should be strengthened out? Each > one of those has a little bit different semantic/meaning, but at the same > time they are very similar. For single input operators `endInput()` and > `finish()` are actually the very same thing. > > Piotrek > > czw., 15 lip 2021 o 16:47 Till Rohrmann <trohrm...@apache.org> napisał(a): > > > Thanks for updating the FLIP. Based on the new section about > > stop-with-savepoint [--drain] I got two other questions: > > > > 1) Does endOfInput entail sending of the MAX_WATERMARK? > > > > 2) StreamOperator.finish says to flush all buffered events. Would a > > WindowOperator close all windows and emit the results upon calling > > finish, for example? > > > > Cheers, > > Till > > > > On Thu, Jul 15, 2021 at 10:15 AM Till Rohrmann <trohrm...@apache.org> > > wrote: > > > > > Thanks a lot for your answers and clarifications Yun. > > > > > > 1+2) Agreed, this can be a future improvement if this becomes a > problem. > > > > > > 3) Great, this will help a lot with understanding the FLIP. > > > > > > Cheers, > > > Till > > > > > > On Wed, Jul 14, 2021 at 5:41 PM Yun Gao <yungao...@aliyun.com.invalid> > > > wrote: > > > > > >> Hi Till, > > >> > > >> Very thanks for the review and comments! > > >> > > >> 1) First I think in fact we could be able to do the computation > outside > > >> of the main thread, > > >> and the current implementation mainly due to the computation is in > > >> general fast and we > > >> initially want to have a simplified first version. > > >> > > >> The main requirement here is to have a constant view of the state of > the > > >> tasks, otherwise > > >> for example if we have A -> B, if A is running when we check if we > need > > >> to trigger A, we will > > >> mark A as have to trigger, but if A gets to finished when we check B, > we > > >> will also mark B as > > >> have to trigger, then B will receive both rpc trigger and checkpoint > > >> barrier, which would break > > >> some assumption on the task side and complicate the implementation. > > >> > > >> But to cope this issue, we in fact could first have a snapshot of the > > >> tasks' state and then do the > > >> computation, both the two step do not need to be in the main thread. > > >> > > >> 2) For the computation logic, in fact currently we benefit a lot from > > >> some shortcuts on all-to-all > > >> edges and job vertex with all tasks running, these shortcuts could do > > >> checks on the job vertex level > > >> first and skip some job vertices as a whole. With this optimization we > > >> have a O(V) algorithm, and the > > >> current running time of the worst case for a job with 320,000 tasks is > > >> less than 100ms. For > > >> daily graph sizes the time would be further reduced linearly. > > >> > > >> If we do the computation based on the last triggered tasks, we may not > > >> easily encode this information > > >> into the shortcuts on the job vertex level. And since the time seems > to > > >> be short, perhaps it is enough > > >> to do re-computation from the scratch in consideration of the tradeoff > > >> between the performance and > > >> the complexity ? > > >> > > >> 3) We are going to emit the EndOfInput event exactly after the > finish() > > >> method and before the last > > >> snapshotState() method so that we could shut down the whole topology > > with > > >> a single final checkpoint. > > >> Very sorry for not include enough details for this part and I'll > > >> complement the FLIP with the details on > > >> the process of the final checkpoint / savepoint. > > >> > > >> Best, > > >> Yun > > >> > > >> > > >> > > >> ------------------------------------------------------------------ > > >> From:Till Rohrmann <trohrm...@apache.org> > > >> Send Time:2021 Jul. 14 (Wed.) 22:05 > > >> To:dev <dev@flink.apache.org> > > >> Subject:Re: [RESULT][VOTE] FLIP-147: Support Checkpoint After Tasks > > >> Finished > > >> > > >> Hi everyone, > > >> > > >> I am a bit late to the voting party but let me ask three questions: > > >> > > >> 1) Why do we execute the trigger plan computation in the main thread > if > > we > > >> cannot guarantee that all tasks are still running when triggering the > > >> checkpoint? Couldn't we do the computation in a different thread in > > order > > >> to relieve the main thread a bit. > > >> > > >> 2) The implementation of the DefaultCheckpointPlanCalculator seems to > go > > >> over the whole topology for every calculation. Wouldn't it be more > > >> efficient to maintain the set of current tasks to trigger and check > > >> whether > > >> anything has changed and if so check the succeeding tasks until we > have > > >> found the current checkpoint trigger frontier? > > >> > > >> 3) When are we going to send the endOfInput events to a downstream > task? > > >> If > > >> this happens after we call finish on the upstream operator but before > > >> snapshotState then it would be possible to shut down the whole > topology > > >> with a single final checkpoint. I think this part could benefit from a > > bit > > >> more detailed description in the FLIP. > > >> > > >> Cheers, > > >> Till > > >> > > >> On Fri, Jul 2, 2021 at 8:36 AM Yun Gao <yungao...@aliyun.com.invalid> > > >> wrote: > > >> > > >> > Hi there, > > >> > > > >> > Since the voting time of FLIP-147[1] has passed, I'm closing the > vote > > >> now. > > >> > > > >> > There were seven +1 votes ( 6 / 7 are bindings) and no -1 votes: > > >> > > > >> > - Dawid Wysakowicz (binding) > > >> > - Piotr Nowojski(binding) > > >> > - Jiangang Liu (binding) > > >> > - Arvid Heise (binding) > > >> > - Jing Zhang (binding) > > >> > - Leonard Xu (non-binding) > > >> > - Guowei Ma (binding) > > >> > > > >> > Thus I'm happy to announce that the update to the FLIP-147 is > > accepted. > > >> > > > >> > Very thanks everyone! > > >> > > > >> > Best, > > >> > Yun > > >> > > > >> > [1] https://cwiki.apache.org/confluence/x/mw-ZCQ > > >> > > >> > > >
