Sounds like a good plan to me. On 08/12/2022 08:58, Yun Gao wrote:
Hi Dawid,Very thanks for the discussion and sorry for the delayed response since I was hesitated on some points. But as a whole, with some more thought, first I agree with that addingthe trigger() / cancle() methods to some kind of timer object is not necessaryfor us to achieve the exactly-once for the operators. We could follow thedirection of "modifying the implementation of the operators" to achieve thesame target.But continue to think with this direction, it now looks to me it is also notneeded to add the callback to the timer services:1. For InternalTimerService, the operators could just call `InternalTimerService#forEachProcessingTimer()` on finish to handle the pending timers.2. For the timers registered to the underlying ProcessingTimerService, at least in the currently listed scenarios, the operators itself knows what is the remaining work(e.g., the FileWriter knows if it has in-progress file to flush). Operators could handle the remaining timers in finish() method.Then the only interface we need to consider is that added to the ProcessFunction. Thecurrent interface also looks ok to me.If you think the above option works, I could first have a PoC that demonstrate it is sufficient to only modify the operator implementation to handling the remaining workers properly on finish(). If there are new issues I'll post here and we could have some more discussion.Best, Yun Gao ------------------Original Mail ------------------ *Sender:*Dawid Wysakowicz <dwysakow...@apache.org> *Send Date:*Fri Dec 2 21:21:25 2022 *Recipients:*Dev <dev@flink.apache.org> *Subject:*Re: [DISCUSS] FLIP-269: Properly Handling the Processing Timers on Job Termination Ad. 1 I'd start with ProcessingTimerService as that's the only public interface. It is exposed in the Sink V2 interface. In this scenario it would be the Sink interface that need to extend from a EOFTimersHandler. I believe it would be hard to pass it from there to the ProcessingTimeService as it is passed from the outside e.g. in the ProcessingTimeServiceAware. For that reason I'd go with a registration method in that interface. In ProcessFunction I'd go with a mixin approach, so a ProcessFunction can extend from EOFTimersHandler. I'd do that because ProcessFunction does not have an init/open method where we could register the handler. On operator level I'd have a registration method in InternalTimerService. I believe that's the only way to handle the above ProcessFunction aproach. E.g. in KeyedProcessOperator you need to check if the UDF extend from the interface not the operator itself. Ad. 2 I'd go with *(Keyed)ProcessFunction:* interface EOFTimersHandler { void handleProcessingTimer(long timestamp, Context); } interface Context { public abstract <X> void output(OutputTag<X> outputTag, X value); public abstract K getCurrentKey(); // we can extend it for waitFor later } *ProcessingTimeService: * interface EOFTimersHandler { void handleProcessingTimer(long timestamp, Context); } interface Context { // we can extend it for waitFor later } *InternalTimeService:* interface EOFTimersHandler { void handleProcessingTimer(InternalTimer<K,N> timer Context); } interface Context { // we can extend it for waitFor later } Personally I'd not try to unify those places too much. They have also different visibilities (public/internal), have access to different set of metadata (key/namespace). Ad 3. I don't like the having the trigger/cancel methods, because: 1. I don't like the back and forth between system and UDF 2. Yes, the biggest issue I have is with the possibility with registering new timers. I am trying to be on the safe side here. I don't like the idea of dropping them, because it is again making assumptions what users do with those timers. What if they e.g. emit counter if it reached certain threshold? We'd need an additional flag in the method that is the final timer. My sentiment is that we're making it questionably easier to trigger a timer for the cost of openning up for unforeseen problems with follow up registration. Best, Dawid On 30/11/2022 12:13, Yun Gao wrote: Hi Dawid, PiotrVery thanks for the discussion!As a whole I think we are already consistent with the callback option, and I don't think I opposed that we could modify the current internal implementation. But from my side it is still not clear what the actual interfaces are proposing. Let me first try to summarize that a bit:1) Which object does the handlers register on?It seems there are two options, one is to timer services (InternalTimerService/ ProcessingTimerService or some equivalent things after refactoring), the otherone is as a lifecycle of the operator. I'm now tending to the latter one, how do you think on this part?2) What is the interface of the handler?Option 1 is that interface SomeHandlerName { void processingTimer(Timer timer);}class Timer { long getTimestamp(); void trigger(); void cancel(); // Other actions if required. }But it seems there is controversy on whether to add actions to the timer class. If without that, with my understanding the interfaces of the Option 2 areinterface SomeHandlerName { void processTimer(Timer timer); }interface KeyedSomeHandlerName<KEY, NAMESPACE> { void processKeyedTimer(KeyedTimer<KEY, NAMESPACE> timer, Context ctx); }class Timer { long getTimestamp();}class KeyedTimer<KEY, NAMESPACE> extends Timer { KEY getKey(); NAMESPACE getNamespace();}void Context {void executeAtScheduledTime(Consumer<timer> handler);}As Piotr has pointed out, if we could eliminate the logic of namespace, we could thenremove the namespace related type parameter and method from the interfaces.Do I understand right?Besides, I'm still fully got the reason that why we should not add the actions to the timer class, in consideration that it seems in most cases users could implement their logical with simply calling timer.trigger() (I think the repeat registration is indeed a problem, but I think we could ignore the timers registered during termination). Could you further enlighten me a bit on this part?Best,Yun Gao------------------------------------------------------------------From:Piotr Nowojski<pnowoj...@apache.org>Send Time:2022 Nov. 30 (Wed.) 17:10To:dev<dev@flink.apache.org>Subject:Re: [DISCUSS] FLIP-269: Properly Handling the Processing Timers on Job TerminationHi,I have a couple of remarks.First a general one. For me the important part in the design of this API ishow to expose this to Flink users in public interfaces. NamelyProcessFunction and StreamOperator. InternalTimerService is an internalclass, so we can change it and break it as needed in the future.For registering a handler like proposed by Dawid:interface SomeHandlerName { void onTimer(/* whatever type it is */ timer, Context ctx ) { }}makes sense to me. For the InternalTimerService I think it doesn't mattertoo much what we do. We could provide a similar interface as for theProcessFunction/StreamOperator, it doesn't have to be the same one. On thecontrary, I think it shouldn't be the same, as part of this effort weshouldn't be exposing the concept of `Namespaces` to the public facing API.Re the "waitFor". Theoretically I see arguments why users might want to usethis, but I'm also not convinced whether that's necessary in practice. Iwould be +1 either way. First version can be without this functionality andwe can add it later (given that we designed a good place to add it in thefuture, like the `Context` proposed by Dawid). But I'm also fine adding itnow if others are insisting.Best,Piotrekśr., 30 lis 2022 o 09:18 Dawid Wysakowicz<dwysakow...@apache.org>napisał(a): WindowOperator is not implemented by users. I can see that forInternalTimerService we'll needinterface PendingTimerProcessor<KEY, NAMESPACE> {void onTimer(InternalTimer<KEY, NAMESPACE> timer) {doHandleTimer(timer);}I don't see a problem with that.As you said ProcessingTimeService is a user facing interface andcompletely unrelated to the InternalTimerService. I don't see a reasonwhy we'd need to unify those.As for the waitFor behaviour. Personally, I have not been convinced itis necessary. Maybe it's just my lack of vision, but I can't think of ascenario where I'd use it. Still if we need it, I'd go for something like:void onTimer(/* whatever type it is */ timer, Context ctx ) {}interface Context {void executeAtScheduledTime(Consumer<timer> handler);}That way you have independent simple interfaces that need to work onlyin a single well defined scenario and you don't need to match aninterface to multiple different cases.Best,DawidOn 30/11/2022 07:27, Yun Gao wrote: Hi Dawid,Thanks for the comments!As a whole I'm also open to the API and I also prefer to use simplebut flexible interfaces, but it still looks there are some problem tojust let users to implement the termination actions.Let's take the WindowOperator as an example. As seen in [1],in the timer processing logic it needs to acquire the key / namespaceinformation bound to the timer (which is only supported by the InternalTimerService). Thus if we want users to implement the same logic on termination, we either let users to trigger the timer handler directly or we also allows users to access these piece of information. If we go with the later direction, we might need to provide interfaces like interface PendingTimerProcessor<KEY, NAMESPACE> {void onTimer(Timer<KEY, NAMESPACE> timer) {doHandleTimer(timer);}}class Timer<KEY, NAMESPACE> {long getTimestamp();KEY getKey();NAMESPACE getNamespace();}Then we'll have the issue that since we need the interface to handle both of cases of InternalTimerSerivce and raw ProcessTimeService, the later do not have key and namespace information attached, and its also be a bit inconsistency for users to have to set the KEY and NAMESPACE types.Besides, it looks to me that if we want to implement behaviors like waiting for, it might be not simply reuse the time handler time, then it requires every operator authors to re-implement such waiting logics. Moreover it still have the downside that if you call back to the `onTimer` method after `trigger` you have access to the Context which lets you register new timers. I think we could simply drop the timers registered during we start processing the pending timers on termination. Logically there should be no new data after termination. I think I am not convinced to these arguments. First of all I'm afraid there is no clear distinction in that area what is runtime and what is not. I always found `AbstracStreamOperator(*)` actually part of runtime or Flink's internals and thus I don't find `InternalTimerService` a utility, but a vital part of the system. Let's be honest it is impossible to implement an operator without extending from `AbstractStreamOperator*`.What would be the problem with having a proper implementation in `InternalTimerService`? Can't we do it like this?: I think the original paragraph is only explanation to that the interface is harder to support if we allows the users to implement the arbitrary logic. But since now we are at the page with the callback option, users could always be allowed to implement arbitrary logic no matter we support timer.trigger() or not, thus I think now there is no divergence on this point. I also believe in we'll finally have some logic similar to the proposed one that drain all the times and process it.Best,Yun Gao[1] https://github.com/apache/flink/blob/a7fdab8b23cddf568fa32ee7eb804d7c3eb23a35/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/WindowOperator.java#L488 <https://github.com/apache/flink/blob/a7fdab8b23cddf568fa32ee7eb804d7c3eb23a35/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/WindowOperator.java#L488 ><https://github.com/apache/flink/blob/a7fdab8b23cddf568fa32ee7eb804d7c3eb23a35/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/WindowOperator.java#L488 <https://github.com/apache/flink/blob/a7fdab8b23cddf568fa32ee7eb804d7c3eb23a35/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/WindowOperator.java#L488 > ------------------------------------------------------------------From:Dawid Wysakowicz<dwysakow...@apache.org>Send Time:2022 Nov. 28 (Mon.) 23:33To:dev<dev@flink.apache.org>Subject:Re: [DISCUSS] FLIP-269: Properly Handling the Processing Timers on Job Termination Do we really need to have separate methods for triggering/waiting/cancelling. To me it sounds rather counterintuitive. Whycan't users just execute whatever they want in the handler itself insteadof additional back and forth with the system? Moreover it still have thedownside that if you call back to the `onTimer` method after `trigger` youhave access to the Context which lets you register new timers. I find following approach much simpler:void onTimer(...) {doHandleTimer(timestamp);}void processPendingTimer(...) {// triggerdoHandleTimer(timestamp);// for cancel, simply do nothing...}Sorry I might not make it very clear here. I think the difficulty with supported setting the currentKey is a special issue for the callbackoptions (no matter what the interface is) since it allows users to executelogic other than the one registered with the timers. The complexity comesfrom that currently we have two level of TimerServices: TheProcessingTimerService (there is no key) and InternalTimerService (withkey). Currently only ProcessingTimerService is exposed to the runtime andInternalTimerService is much more a utility to implement the operator. Thenwith the current code, the runtime could only access toProcessingTimerService on termination. I think I am not convinced to these arguments. First of all I'm afraid there is no clear distinction in that area what is runtime and what is not.I always found `AbstracStreamOperator(*)` actually part of runtime orFlink's internals and thus I don't find `InternalTimerService` a utility,but a vital part of the system. Let's be honest it is impossible toimplement an operator without extending from `AbstractStreamOperator*`. What would be the problem with having a proper implementation in `InternalTimerService`? Can't we do it like this?: AbstractStreamOperator#finish() {internalTimerService.finish();}InternalTimerService#finish() {while ((timer = processingTimeTimersQueue.peek()) != null) {keyContext.setCurrentKey(timer.getKey());processingTimeTimersQueue.poll();onEndOfInputHandler.processPendingTimer(timer);}}If we only executes some predefined actions, we do not need to worry about the implementation of InternalTimerService and just execute theregistered timers. But if we allow users to execute arbitrary logic, weneed to be also aware of the InternalTimerServices and parse the key fromthe timers stored in it. I think we should always have method to overcomethis issue, but to support the callback options would be more complex. I am not sure, having "predefined actions" would be good enough that we do not need to set a key. As a user I'd anyhow expect the proper key to beset in processPendingTimer. Best,DawidOn 24/11/2022 08:51, Yun Gao wrote:Hi Piotr / Divye, Very thanks for the discussion! First IMO it seems we have reached the consensus on the high-level API: Most operators shouldusually have only one reasonable action to the pending timers ontermination, thus we could let the operators to implement its own actionswith the low-level interface provided. The only exception is theProcessFunction, with which users might register customized timers, thususers might also defines the actions on termination (If I havemisunderstandings here, please correct me). For the low-level API, I couldget the benefits with the callback options: since in most cases an operatorhas only one action to all the timers, its a waste for us to store the sameflag for all the timers, also with a lot of code / state format changes.But since it is enough for most users to simply trigger / cacnel thetimers, it would be redundant for users to implement the logic twice. Thusperhaps we might combine the benefits of the two options: We might have aseparate interface public interface TimerHandlersOnTermination { voidprocessPendingTimer(Timer timer, long currentTime); } public class Timer {long getRegisteredTimestamp(); void trigger(); void waitFor(); voidcancel(); } Then if an operator have implemented theTimerHandlersOnTermination interface, on termination we could callprocessPendingTimer(xx) for every pending timers. Users might simplytrigger / waitFor / cancel it, or execute some other logics if needed. Thenfor the ProcessFunction we might have a similar interface toprocessPendingTimer, except we might need to provide Context / Collector tothe ProcessFunction. Do you think this would be a good direction? Also@Piotr I don't see a problem here. Interface doesn't have to reflect that,only the runtime must set the correct key context before executing thehandler dealing with the processing time timers at the end of input/time.Sorry I might not make it very clear here. I think the difficulty withsupported setting the currentKey is a special issue for the callbackoptions (no matter what the interface is) since it allows users to executelogic other than the one registered with the timers. The complexity comesfrom that currently we have two level of TimerServices: TheProcessingTimerService (there is no key) and InternalTimerService (withkey). Currently only ProcessingTimerService is exposed to the runtime andInternalTimerService is much more a utility to implement the operator. Thenwith the current code, the runtime could only access toProcessingTimerService on termination. If we only executes some predefinedactions, we do not need to worry about the implementation ofInternalTimerService and just execute the registered timers. But if weallow users to execute arbitrary logic, we need to be also aware of theInternalTimerServices and parse the key from the timers stored in it. Ithink we should always have method to overcome this issue, but to supportthe callback options would be more complex. Best, Yun Gao------------------------------------------------------------------From:Divye Kapoor<dkap...@pinterest.com.INVALID> <mailto:dkap...@pinterest.com.INVALID > Send Time:2022 Nov. 24 (Thu.) 08:50To:dev<dev@flink.apache.org> <mailto:dev@flink.apache.org > Cc:XenonDevelopment Team<xenon-...@pinterest.com> <mailto:xenon-...@pinterest.com Subject:Re: Re: [DISCUSS] FLIP-269: Properly Handling the Processing Timers on Job Termination Sounds good. Looks like we're on the same page.Thanks! Divye On Wed, Nov 23, 2022 at 2:41 AM Piotr Nowojski <pnowoj...@apache.org> <mailto:pnowoj...@apache.org > wrote: Hi Divye Ithink we are mostly on the same page. Just to clarify/rephrase: One thingto think about - on EOF “trigger immediately” will mean that theasynchronous wait timeout timers will also fire - which is undesirable Ididn't mean to fire all timers immediately in all of the built-inoperators. Just that each built-in operator can have a hard coded way(without a way for users to change it) to handle those timers. Windowedoperators would trigger the lingering timers (flush outputs),AsyncWaitOperator could just ignore them. The same way users could registerEOF timer handlers in the ProcessFunction as Dawid Wysakowicz proposed, we(as flink developers) could use the same mechanism to implement anybehaviour we want for the built-in operators. There should be no need toadd any separate mechanism. Best, Piotrek śr., 23 lis 2022 o 08:21 DivyeKapoor<dkap...@pinterest.com.invalid> <mailto:dkap...@pinterest.com.invalid > napisał(a): Thanks Yun/Piotrek, Somebrief comments inline below. On Tue, Nov 22, 2022 at 1:37 AM Piotr Nowojski<pnowoj...@apache.org> <mailto:pnowoj...@apache.org > wrote: Hi, All inall I would agree with Dawid's proposal. +1 We can add the flexibility ofhow to deal with the timers in the low level API via adding a handler - ifsomeone needs to customize it, he will always have a workaround. Note aftergiving it more thought, I agree that registering some handlers is betterthan overloading the register timer method and modifying the timer's state.+1. At the same time, we can force the most sensible semantic that we thinkfor the couple of built-in operators, which should be prettystraightforward (either ignore the timers, or fire them at once). I agreethere might be some edge cases, that theoretically user might want to waitfor the timer to fire naturally, but: 1. I'm not sure how common inpractice this will be. If not at all, then why should we be complicatingthe API/system? That’s fair. However, the specifics are very importanthere. One thing to think about - on EOF “trigger immediately” will meanthat the asynchronous wait timeout timers will also fire - which isundesirable (because they are racing with the last async call). However,the issue is cleanly resolved by waiting for the timer to be canceled whenthe last event is processed. (“Wait for” case). Ignoring the timer has theleast justification. Registering the handler as per Dawid’s proposal andhaving that handler unregister the timers on EOF makes best sense. Thissolution also unifies the trigger immediately case as that handler canreregister the timers for early termination. The proposal: 1. Operatorreceives EOF 2. EOF timer handler triggers 3. EOF handler adjusts theregistered timers for early trigger or ignore. If wait-for behavior isdesired, timers are not changed. This is controlled in client code. 4.Operator waits for all timers to drain/trigger. (“Always”). There is nospecial handling for ignore/early trigger. 5. Operator allows job toproceed with shutdown. The only api change needed is an EOF handler. Theother agreement we need is that “Wait for” is the desired behavior inprocessing time and that processing time is fundamentally different fromevent time in this respect. (I have changed my thinking since the lastmail). 2. We can always expand the API in the future, and let the useroverride the default built-in behaviour of the operators via some setter onthe stream transformation (`SingleOutputStreamOperator`), or via somecustom API DSL style in each of the operators separately. This is notrequired. See above. Re forcing the same semantics for processing timetimers as for event time ones - this is tempting, but indeed I see apossibility that users need to adhere to some external constraints whenusing processing time. +1. As above, we should consider the 2 casesfundamentally different in this area. Re: Yun - b) Another issue is thatwhat if users use timers with different termination actions in the sameoperator / UDF? For example, users use some kind of timeout (like throwsexception if some thing not happen after some other thing), and also somekind of window aggregation logic. In this case, without additional tags,users might not be able to distinguish which timer should be canceled andwhich time should be triggered ? as above. The EOF handler makes thechoice. 4. How could these scenarios adjust their APIs ? From the currentlisted scenarios, I'm more tend to that as @Dawid pointed out, there mightbe only one expected behavior for each scenario, thus it does not seems toneed to allow users to adjust the behavior. Thus @Divye may I have a doubleconfirmation currently do we have explicit scenarios that is expected tochange the different behaviors for the same scenario? Wait-for behavior isprobably the only expected behavior and any alterations should be from theEOF handler managing the registered timers. Besides @Divye from the listedscenarios, I have another concern for global configuration is that for onejob, different operators seems to still might have different expectedbehaviors. For example, A job using both Window operator andAsyncWaitOperator might have different requirements for timers ontermination? Thank you for raising this case. This changed my thinking.Based on your point, we should try and align on the “Wait-for” with EOFhandler proposal. I’m withdrawing the “single-runtime-config” proposal.Best, Divye
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