Hi Dawid, Piotr
Very 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 other
one 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 are
interface 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 then
remove 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.) 17:10
To:dev <dev@flink.apache.org>
Subject:Re: [DISCUSS] FLIP-269: Properly Handling the Processing Timers on Job
Termination
Hi,
I have a couple of remarks.
First a general one. For me the important part in the design of this API is
how to expose this to Flink users in public interfaces. Namely
ProcessFunction and StreamOperator. InternalTimerService is an internal
class, 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 matter
too much what we do. We could provide a similar interface as for the
ProcessFunction/StreamOperator, it doesn't have to be the same one. On the
contrary, I think it shouldn't be the same, as part of this effort we
shouldn't be exposing the concept of `Namespaces` to the public facing API.
Re the "waitFor". Theoretically I see arguments why users might want to use
this, but I'm also not convinced whether that's necessary in practice. I
would be +1 either way. First version can be without this functionality and
we can add it later (given that we designed a good place to add it in the
future, like the `Context` proposed by Dawid). But I'm also fine adding it
now if others are insisting.
Best,
Piotrek
śr., 30 lis 2022 o 09:18 Dawid Wysakowicz <dwysakow...@apache.org>
napisał(a):
> WindowOperator is not implemented by users. I can see that for
> InternalTimerService we'll need
>
> interface 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 and
> completely unrelated to the InternalTimerService. I don't see a reason
> why we'd need to unify those.
>
> As for the waitFor behaviour. Personally, I have not been convinced it
> is necessary. Maybe it's just my lack of vision, but I can't think of a
> scenario 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 only
> in a single well defined scenario and you don't need to match an
> interface to multiple different cases.
>
> Best,
> Dawid
>
> On 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 simple
> > but flexible interfaces, but it still looks there are some problem to
> > just 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 / namespace
> > information 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.) 23:33
> > To: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. Why
> can't users just execute whatever they want in the handler itself instead
> of additional back and forth with the system? 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 find following approach much simpler:
> > void onTimer(...) {
> > doHandleTimer(timestamp);
> > }
> > void processPendingTimer(...) {
> > // trigger
> > doHandleTimer(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 callback
> options (no matter what the interface is) since it allows users to execute
> logic other than the one registered with the timers. The complexity comes
> from that currently we have two level of TimerServices: The
> ProcessingTimerService (there is no key) and InternalTimerService (with
> key). Currently only ProcessingTimerService is exposed to the runtime and
> InternalTimerService is much more a utility to implement the operator. Then
> with the current code, the runtime could only access to
> ProcessingTimerService 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 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?:
> > 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 the
> registered timers. But if we allow users to execute arbitrary logic, we
> need to be also aware of the InternalTimerServices and parse the key from
> the timers stored in it. I think we should always have method to overcome
> this 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 be
> set in processPendingTimer.
> > Best,
> > Dawid
> > On 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 should
> usually have only one reasonable action to the pending timers on
> termination, thus we could let the operators to implement its own actions
> with the low-level interface provided. The only exception is the
> ProcessFunction, with which users might register customized timers, thus
> users might also defines the actions on termination (If I have
> misunderstandings here, please correct me). For the low-level API, I could
> get the benefits with the callback options: since in most cases an operator
> has only one action to all the timers, its a waste for us to store the same
> flag 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 the
> timers, it would be redundant for users to implement the logic twice. Thus
> perhaps we might combine the benefits of the two options: We might have a
> separate interface public interface TimerHandlersOnTermination { void
> processPendingTimer(Timer timer, long currentTime); } public class Timer {
> long getRegisteredTimestamp(); void trigger(); void waitFor(); void
> cancel(); } Then if an operator have implemented the
> TimerHandlersOnTermination interface, on termination we could call
> processPendingTimer(xx) for every pending timers. Users might simply
> trigger / waitFor / cancel it, or execute some other logics if needed. Then
> for the ProcessFunction we might have a similar interface to
> processPendingTimer, except we might need to provide Context / Collector to
> the 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 the
> handler 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 with
> supported setting the currentKey is a special issue for the callback
> options (no matter what the interface is) since it allows users to execute
> logic other than the one registered with the timers. The complexity comes
> from that currently we have two level of TimerServices: The
> ProcessingTimerService (there is no key) and InternalTimerService (with
> key). Currently only ProcessingTimerService is exposed to the runtime and
> InternalTimerService is much more a utility to implement the operator. Then
> with the current code, the runtime could only access to
> ProcessingTimerService on termination. If we only executes some predefined
> actions, we do not need to worry about the implementation of
> InternalTimerService and just execute the registered timers. But if we
> allow users to execute arbitrary logic, we need to be also aware of the
> InternalTimerServices and parse the key from the timers stored in it. I
> think we should always have method to overcome this issue, but to support
> the 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.) 08:50
> To:dev <dev@flink.apache.org> <mailto:dev@flink.apache.org > Cc:Xenon
> Development 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 I
> think we are mostly on the same page. Just to clarify/rephrase: One thing
> to think about - on EOF “trigger immediately” will mean that the
> asynchronous wait timeout timers will also fire - which is undesirable I
> didn't mean to fire all timers immediately in all of the built-in
> operators. Just that each built-in operator can have a hard coded way
> (without a way for users to change it) to handle those timers. Windowed
> operators would trigger the lingering timers (flush outputs),
> AsyncWaitOperator could just ignore them. The same way users could register
> EOF timer handlers in the ProcessFunction as Dawid Wysakowicz proposed, we
> (as flink developers) could use the same mechanism to implement any
> behaviour we want for the built-in operators. There should be no need to
> add any separate mechanism. Best, Piotrek śr., 23 lis 2022 o 08:21 Divye
> Kapoor <dkap...@pinterest.com.invalid> <mailto:
> dkap...@pinterest.com.invalid > napisał(a): Thanks Yun/Piotrek, Some
> brief comments inline below. On Tue, Nov 22, 2022 at 1:37 AM Piotr Nowojski
> <pnowoj...@apache.org> <mailto:pnowoj...@apache.org > wrote: Hi, All in
> all I would agree with Dawid's proposal. +1 We can add the flexibility of
> how to deal with the timers in the low level API via adding a handler - if
> someone needs to customize it, he will always have a workaround. Note after
> giving it more thought, I agree that registering some handlers is better
> than 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 think
> for the couple of built-in operators, which should be pretty
> straightforward (either ignore the timers, or fire them at once). I agree
> there might be some edge cases, that theoretically user might want to wait
> for the timer to fire naturally, but: 1. I'm not sure how common in
> practice this will be. If not at all, then why should we be complicating
> the API/system? That’s fair. However, the specifics are very important
> here. One thing to think about - on EOF “trigger immediately” will mean
> that the asynchronous wait timeout timers will also fire - which is
> undesirable (because they are racing with the last async call). However,
> the issue is cleanly resolved by waiting for the timer to be canceled when
> the last event is processed. (“Wait for” case). Ignoring the timer has the
> least justification. Registering the handler as per Dawid’s proposal and
> having that handler unregister the timers on EOF makes best sense. This
> solution also unifies the trigger immediately case as that handler can
> reregister the timers for early termination. The proposal: 1. Operator
> receives EOF 2. EOF timer handler triggers 3. EOF handler adjusts the
> registered timers for early trigger or ignore. If wait-for behavior is
> desired, timers are not changed. This is controlled in client code. 4.
> Operator waits for all timers to drain/trigger. (“Always”). There is no
> special handling for ignore/early trigger. 5. Operator allows job to
> proceed with shutdown. The only api change needed is an EOF handler. The
> other agreement we need is that “Wait for” is the desired behavior in
> processing time and that processing time is fundamentally different from
> event time in this respect. (I have changed my thinking since the last
> mail). 2. We can always expand the API in the future, and let the user
> override the default built-in behaviour of the operators via some setter on
> the stream transformation (`SingleOutputStreamOperator`), or via some
> custom API DSL style in each of the operators separately. This is not
> required. See above. Re forcing the same semantics for processing time
> timers as for event time ones - this is tempting, but indeed I see a
> possibility that users need to adhere to some external constraints when
> using processing time. +1. As above, we should consider the 2 cases
> fundamentally different in this area. Re: Yun - b) Another issue is that
> what if users use timers with different termination actions in the same
> operator / UDF? For example, users use some kind of timeout (like throws
> exception if some thing not happen after some other thing), and also some
> kind of window aggregation logic. In this case, without additional tags,
> users might not be able to distinguish which timer should be canceled and
> which time should be triggered ? as above. The EOF handler makes the
> choice. 4. How could these scenarios adjust their APIs ? From the current
> listed scenarios, I'm more tend to that as @Dawid pointed out, there might
> be only one expected behavior for each scenario, thus it does not seems to
> need to allow users to adjust the behavior. Thus @Divye may I have a double
> confirmation currently do we have explicit scenarios that is expected to
> change the different behaviors for the same scenario? Wait-for behavior is
> probably the only expected behavior and any alterations should be from the
> EOF handler managing the registered timers. Besides @Divye from the listed
> scenarios, I have another concern for global configuration is that for one
> job, different operators seems to still might have different expected
> behaviors. For example, A job using both Window operator and
> AsyncWaitOperator might have different requirements for timers on
> termination? Thank you for raising this case. This changed my thinking.
> Based on your point, we should try and align on the “Wait-for” with EOF
> handler proposal. I’m withdrawing the “single-runtime-config” proposal.
> Best, Divye
>
