Hi,
yes, this is essentially the solution I had in my head but I went a bit
further and generalized it.
Basically, to make triggers composable they should have this interface,
let's call it SimpleTrigger for now:
class SimpleTrigger {
void onElement(T element, long timestamp, W window, TriggerContext ctx);
boolean shouldFire(W window, TriggerContext ctx);
void onMerge(W window, OnMergeContext ctx);
void clear(W window, TriggerContext ctx);
}
notice how onElement() cannot return a TriggerResult anymore and how
onEventTime() and onProcessingTime() of the currently existing Trigger
interface were folded into shouldFire(). Each trigger essentially becomes a
predicate that says at any given time whether they would fire the window.
Having just one method that can decide whether to fire or not makes these
easily composable to form complex triggers, thus enabling the trigger DSL
we want to implement.
The way to go about implementing this is either to replace our current
Trigger interface by this new interface or to keep our more powerful
interface with all the customization options and have one
SimpleTriggerTrigger that can execute a tree of SimpleTriggers. A rough
sketch of this would be this:
https://gist.github.com/aljoscha/66b0fcab89cd2b6190a63899f461067f
Cheers,
Aljoscha
On Mon, 25 Jul 2016 at 14:33 Kostas Kloudas <k.klou...@data-artisans.com>
wrote:
> Hi Aljoscha,
>
> This was exactly one of the problems I also found.
>
> The way I was thinking about it is the following:
>
> Conceptually, time (event and processing) advances but state is a
> fixed property of the window.
>
> Given this, I modified the Count trigger to also ask for the
> current state (count) of the window in all method (e.g. onEventTime and
> onProcessingTime). This way the trigger can be composed and play
> well with the other triggers.
>
> If you have any more ideas on that and the rest of the problems I
> sent in the previous email, please let me know.
>
> Kostas
>
> > On Jul 25, 2016, at 2:22 PM, Aljoscha Krettek <aljos...@apache.org>
> wrote:
> >
> > These are some very interesting thoughts! I have some more, based on
> these:
> >
> > What happens if you have for example this Trigger:
> > All(Watermark.pastEndOfWindow(), Count.atLeast(10))
> >
> > When would this even fire, i.e. what are the steps that lead to this
> > combined trigger firing with the Trigger system that we currently have in
> > place?
> >
> > I have some thoughts but they are not compatible with the way we
> currently
> > handle triggers. I have to think some more, but please shoot if you have
> > any ideas.
> >
> > Cheers,
> > Aljoscha
> >
> > On Fri, 22 Jul 2016 at 13:10 Kostas Kloudas <k.klou...@data-artisans.com
> >
> > wrote:
> >
> >> Forgot to say that the signature for the onFire() that I think fits
> should
> >> be:
> >>
> >> void onFire(Window window, TriggerContext ctx) throws Exception;
> >>
> >>> On Jul 22, 2016, at 12:47 PM, Kostas Kloudas <
> >> k.klou...@data-artisans.com> wrote:
> >>>
> >>> Hi,
> >>>
> >>> I started working on the new triggers proposed here and so far I can
> see
> >>> two shortcomings in the current state of the triggers that do not play
> >> well
> >>> with the new proposals, and more specifically the composite triggers
> All
> >>> and Any.
> >>>
> >>> So here it goes:
> >>>
> >>> 1) In the document posted above, there are some new useful trigger
> >> combinations (like Any and All) which allow
> >>> for combining primitive triggers. This decouples the TriggerResult of
> >> each individual trigger from the action that
> >>> is actually going to be executed. For example, an All trigger may have
> >> one proposing FIRE while the other
> >>> CONTINUE and the final result will be CONTINUE.
> >>>
> >>> In this case, any action that should be taken by each individual
> >> trigger upon firing, e.g. cleaning its state as in the
> >>> case of CountTrigger, should be postponed until the parent trigger
> (All)
> >> decides to fire.
> >>>
> >>> For this, there should be a onFire() method in each trigger that does
> >> exactly that. This method should be called in the
> >>> fireOrCleanup() of the windowOperator, when the firing is successful.
> >>>
> >>> 2) In the current implementation, when stateful triggers, like the
> >> CountTrigger, are combined in a composite Trigger
> >>> (with Any or All) their state is shared because the stateHandle is the
> >> same for both. To solve this, the handle should
> >>> become unique, BUT consistent for the same Trigger. The latter implies
> >> that the handle for the same trigger after
> >>> a node failure, should be the same as that of its predecessor (before
> >> the failure).
> >>>
> >>> Let me know your thoughts on these.
> >>>
> >>> Kostas
> >>>
> >>>
> >>>> On Jul 21, 2016, at 10:24 AM, Aljoscha Krettek <aljos...@apache.org>
> >> wrote:
> >>>>
> >>>> I'm proposing to get this small change into 1.1:
> >>>> https://issues.apache.org/jira/browse/FLINK-4239 This will make our
> >> lives
> >>>> easier with the future proposed changes.
> >>>>
> >>>> What do you think?
> >>>> On Tue, 19 Jul 2016 at 11:41 Aljoscha Krettek <aljos...@apache.org>
> >> wrote:
> >>>>
> >>>>> Hi,
> >>>>> these new features should make it into the 1.2 release. We are
> already
> >>>>> working on releasing 1.1 so it won't make it for that one.
> >> unfortunately.
> >>>>>
> >>>>> Cheers,
> >>>>> Aljoscha
> >>>>>
> >>>>> On Mon, 18 Jul 2016 at 23:19 Chen Qin <qinnc...@gmail.com> wrote:
> >>>>>
> >>>>>> BTW, do you have rough timeline in term of roll out it to
> production?
> >>>>>>
> >>>>>> Thanks,
> >>>>>> Chen
> >>>>>>
> >>>>>>
> >>>>>> On Mon, Jul 18, 2016 at 2:46 AM, Aljoscha Krettek <
> >> aljos...@apache.org>
> >>>>>> wrote:
> >>>>>>
> >>>>>>> Hi,
> >>>>>>> Chen commented this on the doc (I'm mirroring here so everyone can
> >>>>>> follow):
> >>>>>>> "It would be cool to be able to access last snapshot of window
> states
> >>>>>>> before it get purged. Pipeline author might consider put it to
> >> external
> >>>>>>> storage and deal with late arriving events by restore corresponding
> >>>>>>> window."
> >>>>>>>
> >>>>>>> My answer:
> >>>>>>> This is partially covered by the section called "What Happens at
> >>>>>>> Window-Cleanup Time, Who Decides When to Purge". What I want to
> >>>>>> introduce
> >>>>>>> is that the window can have one final emission if there is new data
> >> in
> >>>>>> the
> >>>>>>> buffers at cleanup time.
> >>>>>>>
> >>>>>>> The work on this will also depend on this proposal:
> >>>>>>>
> >>>>>>>
> >>>>>>
> >>
> https://cwiki.apache.org/confluence/display/FLINK/FLIP-2+Extending+Window+Function+Metadata
> >>>>>>> With
> >>>>>>> this, the WindowFunction can get meta data about the window firing
> >> so it
> >>>>>>> could be informed that this is the last firing before a cleanup and
> >> that
> >>>>>>> there already was an earlier, on-time firing.
> >>>>>>>
> >>>>>>> Does this cover your concerns, Chen?
> >>>>>>>
> >>>>>>> Cheers,
> >>>>>>> Aljoscha
> >>>>>>>
> >>>>>>> On Sun, 10 Jul 2016 at 21:24 Chen Qin <qinnc...@gmail.com> wrote:
> >>>>>>>
> >>>>>>>> Sure. Currently, it looks like any element assigned to a too late
> >>>>>> window
> >>>>>>>> will be dropped silently😓 ?
> >>>>>>>>
> >>>>>>>> Having a late window stream imply somehow Flink needs to add one
> >> more
> >>>>>>> state
> >>>>>>>> to window and split window state cleanup from window retirement.
> >>>>>>>> I would suggest as simple as adding a function in trigger called
> >>>>>>>> OnLateElement and always fire_purge it would enable developer
> aware
> >>>>>> and
> >>>>>>>> handle this case.
> >>>>>>>>
> >>>>>>>> Chen
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> On Fri, Jul 8, 2016 at 1:00 AM, Aljoscha Krettek <
> >> aljos...@apache.org
> >>>>>>>
> >>>>>>>> wrote:
> >>>>>>>>
> >>>>>>>>> @Chen I added a section at the end of the document regarding
> access
> >>>>>> to
> >>>>>>>> the
> >>>>>>>>> elements that are dropped as late. Right now, the section just
> >>>>>> mentions
> >>>>>>>>> that we have to do this but there is no real proposal yet for how
> >>>>>> to do
> >>>>>>>> it.
> >>>>>>>>> Only a rough sketch so that we don't forget about it.
> >>>>>>>>>
> >>>>>>>>> On Fri, 8 Jul 2016 at 07:47 Chen Qin <qinnc...@gmail.com> wrote:
> >>>>>>>>>
> >>>>>>>>>> +1 for allowedLateness scenario.
> >>>>>>>>>>
> >>>>>>>>>> The rationale behind is there are backfills or data issues hold
> >>>>>>>> in-window
> >>>>>>>>>> data till watermark pass end time. It cause sink write partial
> >>>>>>> output.
> >>>>>>>>>>
> >>>>>>>>>> Allow high allowedLateness threshold makes life easier to merge
> >>>>>> those
> >>>>>>>>>> results and overwrite partial output with correct output at
> sink.
> >>>>>> But
> >>>>>>>>> yeah,
> >>>>>>>>>> pipeline author is at risk of blow up statebackend with huge
> >>>>>> states.
> >>>>>>>>>>
> >>>>>>>>>> Alternatively, In some case, if sink allows read-check-merge
> >>>>>>> operation,
> >>>>>>>>>> window can explicit call out events ingested after
> >>>>>> allowedLateness.
> >>>>>>> It
> >>>>>>>>> asks
> >>>>>>>>>> pipeline author mitigated these events in a way outside of flink
> >>>>>>>>> ecosystem.
> >>>>>>>>>> The catch is that since everywhere in a flink job can replay and
> >>>>>>>>>> checkpoint, notification should somehow includes these info as
> >>>>>> well.
> >>>>>>>>>>
> >>>>>>>>>> Thanks
> >>>>>>>>>> Chen
> >>>>>>>>>>
> >>>>>>>>>> On Thu, Jul 7, 2016 at 12:14 AM, Kostas Kloudas <
> >>>>>>>>>> k.klou...@data-artisans.com
> >>>>>>>>>>> wrote:
> >>>>>>>>>>
> >>>>>>>>>>> Hi,
> >>>>>>>>>>>
> >>>>>>>>>>> In the effort to move the discussion to the mailing list,
> rather
> >>>>>>> than
> >>>>>>>>> the
> >>>>>>>>>>> doc,
> >>>>>>>>>>> there was a comment in the doc:
> >>>>>>>>>>>
> >>>>>>>>>>> “It seems this proposal marries the allowed lateness of events
> >>>>>> and
> >>>>>>>> the
> >>>>>>>>>>> discarding of window state. In most use cases this should be
> >>>>>>>>> sufficient,
> >>>>>>>>>>> but there are instances where having independent control of
> >>>>>> these
> >>>>>>> may
> >>>>>>>>> be
> >>>>>>>>>>> useful.
> >>>>>>>>>>>
> >>>>>>>>>>> For instance, you may have a job that computes some aggregate,
> >>>>>>> like a
> >>>>>>>>>> sum.
> >>>>>>>>>>> You may want to keep the window state around for a while, but
> >>>>>> not
> >>>>>>> too
> >>>>>>>>>> long.
> >>>>>>>>>>> Yet you may want to continue processing late events after you
> >>>>>>>> discarded
> >>>>>>>>>> the
> >>>>>>>>>>> window state. It is possible that your stream sinks can make
> >>>>>> use of
> >>>>>>>>> this
> >>>>>>>>>>> data. For instance, they may be writing to a data store that
> >>>>>>> returns
> >>>>>>>> an
> >>>>>>>>>>> error if a row already exists, which allow the sink to read the
> >>>>>>>>> existing
> >>>>>>>>>>> row and update it with the new data."
> >>>>>>>>>>>
> >>>>>>>>>>> To which I would like to reply:
> >>>>>>>>>>>
> >>>>>>>>>>> If I understand your use-case correctly, I believe that the
> >>>>>>> proposed
> >>>>>>>>>>> binding of the allowed lateness to the state purging does not
> >>>>>>> impose
> >>>>>>>>> any
> >>>>>>>>>>> problem. The lateness specifies the upper time bound, after
> >>>>>> which
> >>>>>>> the
> >>>>>>>>>> state
> >>>>>>>>>>> will be discarded. Between the start of a window and its (end +
> >>>>>>>>>>> allowedLateness) you can write custom triggers that fire, purge
> >>>>>> the
> >>>>>>>>>> state,
> >>>>>>>>>>> or do nothing. Given this, I suppose that, at the most extreme
> >>>>>>> case,
> >>>>>>>>> you
> >>>>>>>>>>> can specify an allowed lateness of Long.MaxValue and do the
> >>>>>> purging
> >>>>>>>> of
> >>>>>>>>>> the
> >>>>>>>>>>> state "manually". By doing this, you remove the safeguard of
> >>>>>>> letting
> >>>>>>>>> the
> >>>>>>>>>>> system purge the state at some point in time, and you can do
> >>>>>> your
> >>>>>>> own
> >>>>>>>>>>> custom state management that fits your needs.
> >>>>>>>>>>>
> >>>>>>>>>>> Thanks,
> >>>>>>>>>>> Kostas
> >>>>>>>>>>>
> >>>>>>>>>>>> On Jul 6, 2016, at 5:43 PM, Aljoscha Krettek <
> >>>>>>> aljos...@apache.org>
> >>>>>>>>>>> wrote:
> >>>>>>>>>>>>
> >>>>>>>>>>>> @Vishnu Funny you should ask that because I have a design doc
> >>>>>>> lying
> >>>>>>>>>>> around.
> >>>>>>>>>>>> I'll open a new mail thread to not hijack this one.
> >>>>>>>>>>>>
> >>>>>>>>>>>> On Wed, 6 Jul 2016 at 17:17 Vishnu Viswanath <
> >>>>>>>>>>> vishnu.viswanat...@gmail.com>
> >>>>>>>>>>>> wrote:
> >>>>>>>>>>>>
> >>>>>>>>>>>>> Hi,
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> I was going through the suggested improvements in window,
> >>>>>> and I
> >>>>>>>> have
> >>>>>>>>>>>>> few questions/suggestion on improvement regarding the
> >>>>>> Evictor.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> 1) I am having a use case where I have to create a custom
> >>>>>>> Evictor
> >>>>>>>>> that
> >>>>>>>>>>> will
> >>>>>>>>>>>>> evict elements from the window based on the value (e.g., if I
> >>>>>>> have
> >>>>>>>>>>> elements
> >>>>>>>>>>>>> are of case class Item(id: Int, type:String) then evict
> >>>>>> elements
> >>>>>>>>> that
> >>>>>>>>>>> has
> >>>>>>>>>>>>> type="a"). I believe this is not currently possible.
> >>>>>>>>>>>>> 2) this is somewhat related to 1) where there should be an
> >>>>>>> option
> >>>>>>>> to
> >>>>>>>>>>> evict
> >>>>>>>>>>>>> elements from anywhere in the window. not only from the
> >>>>>>> beginning
> >>>>>>>> of
> >>>>>>>>>> the
> >>>>>>>>>>>>> window. (e.g., apply the delta function to all elements and
> >>>>>>> remove
> >>>>>>>>> all
> >>>>>>>>>>>>> those don't pass. I checked the code and evict method just
> >>>>>>> returns
> >>>>>>>>> the
> >>>>>>>>>>>>> number of elements to be removed and processTriggerResult
> >>>>>> just
> >>>>>>>> skips
> >>>>>>>>>>> those
> >>>>>>>>>>>>> many elements from the beginning.
> >>>>>>>>>>>>> 3) Add an option to enables the user to decide if the
> >>>>>> eviction
> >>>>>>>>> should
> >>>>>>>>>>>>> happen before the apply function or after the apply function.
> >>>>>>>>>> Currently
> >>>>>>>>>>> it
> >>>>>>>>>>>>> is before the apply function, but I have a use case where I
> >>>>>> need
> >>>>>>>> to
> >>>>>>>>>>> first
> >>>>>>>>>>>>> apply the function and evict afterward.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> I am doing these for a POC so I think I can modify the flink
> >>>>>>> code
> >>>>>>>>> base
> >>>>>>>>>>> to
> >>>>>>>>>>>>> make these changes and build, but I would appreciate any
> >>>>>>>> suggestion
> >>>>>>>>> on
> >>>>>>>>>>>>> whether these are viable changes or will there any
> >>>>>> performance
> >>>>>>>> issue
> >>>>>>>>>> if
> >>>>>>>>>>>>> these are done. Also any pointer on where to start(e.g, do I
> >>>>>>>> create
> >>>>>>>>> a
> >>>>>>>>>>> new
> >>>>>>>>>>>>> class similar to EvictingWindowOperator that extends
> >>>>>>>>> WindowOperator?)
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> Thanks and Regards,
> >>>>>>>>>>>>> Vishnu Viswanath,
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> On Wed, Jul 6, 2016 at 9:39 AM, Aljoscha Krettek <
> >>>>>>>>> aljos...@apache.org
> >>>>>>>>>>>
> >>>>>>>>>>>>> wrote:
> >>>>>>>>>>>>>
> >>>>>>>>>>>>>> I did:
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>
> >>>>>>>
> >>>>>>
> >>
> https://mail-archives.apache.org/mod_mbox/flink-dev/201606.mbox/%3ccanmxww0abttjjg9ewdxrugxkjm7jscbenmvrzohpt2qo3pq...@mail.gmail.com%3e
> >>>>>>>>>>>>>> ;-)
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> On Wed, 6 Jul 2016 at 15:31 Ufuk Celebi <u...@apache.org>
> >>>>>>> wrote:
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> On Wed, Jul 6, 2016 at 3:19 PM, Aljoscha Krettek <
> >>>>>>>>>> aljos...@apache.org
> >>>>>>>>>>>>
> >>>>>>>>>>>>>>> wrote:
> >>>>>>>>>>>>>>>> In the future, it might be good to to discussions
> >>>>>> directly on
> >>>>>>>> the
> >>>>>>>>>> ML
> >>>>>>>>>>>>>> and
> >>>>>>>>>>>>>>>> then change the document accordingly. This way everyone
> >>>>>> can
> >>>>>>>>> follow
> >>>>>>>>>>>>> the
> >>>>>>>>>>>>>>>> discussion on the ML. I also feel that Google Doc comments
> >>>>>>>> often
> >>>>>>>>>>>>> don't
> >>>>>>>>>>>>>>> give
> >>>>>>>>>>>>>>>> enough space for expressing more complex opinions.
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> I agree! Would you mind raising this point as a separate
> >>>>>>>>> discussion
> >>>>>>>>>> on
> >>>>>>>>>>>>>> dev@
> >>>>>>>>>>>>>>> ?
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>
> >>>>>>>
> >>>>>>
> >>>>>
> >>>
> >>
> >>
>
>
