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From Stephan Ewen <se...@apache.org>
Subject Re: Doubt about window and count trigger
Date Fri, 27 Nov 2015 15:11:32 GMT
Hi!

The reason why trigger state is purged right now with the window is to make
sure that no memory is occupied any more after the purge.
Otherwise, memory consumption would just grow indefinitely, holding state
of old triggers.

Greetings,
Stephan


On Fri, Nov 27, 2015 at 4:05 PM, Fabian Hueske <fhueske@gmail.com> wrote:

> When a window is purged, the Trigger and its state are also cleared.
> A new window comes with a new Trigger (and a new state).
> So yes, in your example the window will be fired after 30 secs again.
>
> Best, Fabian
>
> 2015-11-27 16:01 GMT+01:00 Anwar Rizal <anrizal05@gmail.com>:
>
>> Thanks Fabian,
>>
>> Just for completion.
>> In that 1 min window, is my modified count trigger still valid ? Say, if
>> in that one minute window, I have 100 events after 30 s, it will still fire
>> at 30th second  ?
>>
>> Cheers,
>> anwar.
>>
>>
>>
>> On Fri, Nov 27, 2015 at 3:31 PM, Fabian Hueske <fhueske@gmail.com> wrote:
>>
>>> Hi Anwar,
>>>
>>> You trigger looks good!
>>>
>>> I just want to make sure you know what it is exactly happening after a
>>> window was evaluated and purged.
>>> Once a window was purged, the whole window is cleared and removed. If a
>>> new element arrives, that would have fit into the purged window, a new
>>> window with exactly the same time boundaries is created, i.e., if you have
>>> a 5 min time window, that is fired and purged in minute 4 and a new element
>>> arrived immediately after the purging, it is put into a window, that will
>>> only "exist" for 1 more minute (and not starting a new 5 minute window).
>>>
>>> Cheers, Fabian
>>>
>>>
>>> 2015-11-27 14:59 GMT+01:00 Anwar Rizal <anrizal05@gmail.com>:
>>>
>>>> Thanks Fabian and Aljoscha,
>>>>
>>>> I try to implement the trigger as you described as follow:
>>>>
>>>> https://gist.github.com/anonymous/d0578a4d27768a75bea4
>>>> <https://gist.github.com/anonymous/d0578a4d27768a75bea4>
>>>>
>>>> It works fine , indeed.
>>>>
>>>> Thanks,
>>>> Anwar
>>>>
>>>>
>>>> On Fri, Nov 27, 2015 at 11:49 AM, Aljoscha Krettek <aljoscha@apache.org
>>>> > wrote:
>>>>
>>>>> Hi Anwar,
>>>>> what Fabian wrote is completely right. I just want to give the
>>>>> reasoning for why the CountTrigger behaves as it does. The idea was to
have
>>>>> Triggers that clearly focus on one thing and then at some point add
>>>>> combination triggers. For example, an OrTrigger that triggers if either
of
>>>>> it’s sub triggers triggers, or an AndTrigger that triggers after both
its
>>>>> sub triggers fire. (There is also more complex stuff that could be thought
>>>>> of here.)
>>>>>
>>>>> Cheers,
>>>>> Aljoscha
>>>>> > On 27 Nov 2015, at 09:59, fhueske@gmail.com wrote:
>>>>> >
>>>>> >
>>>>> > Hi,
>>>>> >
>>>>> > a regular tumbling time window of 5 seconds gets all elements within
>>>>> that period of time (semantics of time varies for processing, ingestion,
>>>>> and event time modes) and triggers the execution after 5 seconds.
>>>>> >
>>>>> > If you define a custom trigger, the assignment policy remains the
>>>>> same, but the trigger condition is overwritten (it is NOT additional
but
>>>>> replaces the default condition), i.e., in your implementation, it will
only
>>>>> trigger when 100 elements arrived. In order to trigger also when the
window
>>>>> time expires, you have to register a timer (processing time or event
time
>>>>> timer) via the trigger context.
>>>>> > NOTE: The window assigner will continue to assign elements to the
>>>>> window, even if the window was already evaluated. If you PURGE the window
>>>>> and an element arrives after that, a new window is created.
>>>>> >
>>>>> > To implement your trigger, you have to register a timer in the
>>>>> onEvent() method with:
>>>>> > ctx.registerEventTimeTimer(window.getEnd)
>>>>> > You can to that in every onEvent() call, because the timer is always
>>>>> overwritten.
>>>>> >
>>>>> > NOTE: you should use Flink’s keyed-state (access via triggerContext)
>>>>> if you want to keep state such as the current count.
>>>>> >
>>>>> > Hope this helps. Please let me know if you have further questions.
>>>>> > Fabian
>>>>> >
>>>>> >
>>>>> >
>>>>> >
>>>>> > From: Matthias J. Sax
>>>>> > Sent: Friday, November 27, 2015 08:44
>>>>> > To: user@flink.apache.org
>>>>> > Subject: Re: Doubt about window and count trigger
>>>>> >
>>>>> >
>>>>> > Hi,
>>>>> >
>>>>> > a Trigger is an *additional* condition for intermediate (early)
>>>>> > evaluation of the window. Thus, it is not "or-ed" to the basic window
>>>>> > definition.
>>>>> >
>>>>> > If you want to have an or-ed window condition, you can customize
it
>>>>> by
>>>>> > specifying your own window definition.
>>>>> >
>>>>> > > dataStream.window(new MyOwnWindow() extends WindowAssigner
{ /*
>>>>> put your code here */ );
>>>>> >
>>>>> > -Matthias
>>>>> >
>>>>> >
>>>>> > On 11/26/2015 11:40 PM, Anwar Rizal wrote:
>>>>> > > Hi all,
>>>>> > >
>>>>> > > From the documentation:
>>>>> > > "The |Trigger| specifies when the function that comes after
the
>>>>> window
>>>>> > > clause (e.g., |sum|, |count|) is evaluated (“fires”) for
each
>>>>> window."
>>>>> > >
>>>>> > > So, basically, if I specify:
>>>>> > >
>>>>> > > |keyedStream
>>>>> > >     .window(TumblingTimeWindows.of(Time.of(5, TimeUnit.SECONDS))
>>>>> > >     .trigger(CountTrigger.of(100))|
>>>>> > >
>>>>> > > |
>>>>> > > |
>>>>> > >
>>>>> > > |The execution of the window function is triggered when the
count
>>>>> reaches 100 in the time window of 5 seconds. If you have a system that
>>>>> never reaches 100 in 5 seconds, basically you will never have the window
>>>>> fired.|
>>>>> > >
>>>>> > > |
>>>>> > > |
>>>>> > >
>>>>> > > |My question is, what would be the best option to have behavior
as
>>>>> follow:|
>>>>> > >
>>>>> > > |The execution of the window function is triggered when 5 seconds
>>>>> is reached or 100 events are received before 5 seconds.|
>>>>> > >
>>>>> > >
>>>>> > > I think of implementing my own trigger that looks like
>>>>> CountTrigger, but that will fire also when the end of time window is
>>>>> reached (at the moment, it just returns Continue, instead of Fired).
But
>>>>> maybe there's a better way ?
>>>>> > >
>>>>> > > Is there a reason why CountTrigger is implemented as it is
>>>>> implemented today, and not as I described above (5 seconds or 100 events
>>>>> reached, whichever comes first).
>>>>> > >
>>>>> > >
>>>>> > > Thanks,
>>>>> > >
>>>>> > > Anwar.
>>>>> > >
>>>>>
>>>>>
>>>>
>>>
>>
>

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