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From Álvaro Vilaplana García <alvaro.vilapl...@gmail.com>
Subject Re: Problem with ProcessFunction timeout feature
Date Fri, 23 Jun 2017 09:24:45 GMT
Well, it sounds very reasonable to me!

I will let you know how it goes.


2017-06-23 10:05 GMT+01:00 Stefan Richter <s.richter@data-artisans.com>:

> Yes, exactly. The idea would be, that you operate in event time, but
> combine it with processing time timers to trigger timeout detection. Could
> that help for your case?
>
> Am 23.06.2017 um 10:55 schrieb Álvaro Vilaplana García <
> alvaro.vilaplana@gmail.com>:
>
> Hi Stefan,
>
> You meant
>
> /**
>  * Registers a timer to be fired when processing time passes the given time.
>  *
>  * <p>Timers can internally be scoped to keys and/or windows. When you set a timer
>  * in a keyed context, such as in an operation on
>  * {@link org.apache.flink.streaming.api.datastream.KeyedStream} then that context
>  * will also be active when you receive the timer notification.
>  */
> void registerProcessingTimeTimer(long time);
>
>
> Am i right?
>
>
> Cheers
>
>
> 2017-06-23 9:51 GMT+01:00 Álvaro Vilaplana García <
> alvaro.vilaplana@gmail.com>:
>
>> Hi Stefan,
>>
>> Thank you for your knowledge, very appreciated.
>>
>> According with the documentation:
>>
>> void registerEventTimeTimer(long time); -> 'Registers a timer to be fired
>> when the event time watermark passes the given time.'
>>
>> Dont we have the same problem? We would need an event (that event does
>> not come soon) to set the watermark and trigger the timer.
>>
>> Or there is another way of setting the watermark based on the processing
>> time instead of the event time?
>>
>> Cheers
>>
>> 2017-06-23 9:24 GMT+01:00 Stefan Richter <s.richter@data-artisans.com>:
>>
>>> Hi,
>>>
>>> yes, I think you understood the basic concept of watermarks. Events are
>>> basically driving „the event time clock“, so it can only advance when you
>>> see events. I am not sure if I got the part about partitions correctly, but
>>> the watermark event time is a global thing. For example, if you have
>>> multiple Kafka partitions that your source reads, each partition can have a
>>> different current watermark. However, the source must determine the current
>>> event time of the stream, e.g. as the minimum of the watermarks from all
>>> the Kafka partition it reads.
>>>
>>> One thing that might help for your use case is a combination of event
>>> time and processing time. In the processing function, after each device
>>> event, you could register a timer so far ahead in processing time that it
>>> can serve as a signal to check for time outs because you did not receive
>>> events in a long time.
>>>
>>> Best,
>>> Stefan
>>>
>>> Am 23.06.2017 um 09:51 schrieb Álvaro Vilaplana García <
>>> alvaro.vilaplana@gmail.com>:
>>>
>>> Hi Stefan,
>>>
>>> Thank you so much for your answer.
>>>
>>> Regarding the 'artificial events', our main problem is that we have no
>>> control at all in the devices.
>>>
>>> I have been reading more about event time and watermarks and what I
>>> understood is that when we use event times (device times) Flink does not
>>> know anything about notion of time and the watermark is a way to help Flink
>>> to set the time of the stream (no more events with event time earlier than
>>> the watermark). That would explain that we need always an event to set the
>>> watermark. Does it make sense?
>>>
>>>
>>> I understood that the watermarks will be per partition
>>> (ByKey(deviceId)), is that right?
>>>
>>>
>>> Cheers
>>>
>>> 2017-06-22 16:26 GMT+01:00 Stefan Richter <s.richter@data-artisans.com>:
>>>
>>>> Hi,
>>>>
>>>> if I understand correctly, your problem is that event time does not
>>>> progress in case you don’t receive events, so you cannot detect the timeout
>>>> of devices. Would it make sense to have you source periodically send
>>>> artificial events to advance the watermark in the absence of device events,
>>>> with a certain gap for which you can safely assume that you will no longer
>>>> receive events with a smaller timestamp from any device in the future?
>>>> Because, how else could Flink advance event time without receiving further
>>>> events?
>>>>
>>>> Best,
>>>> Stefan
>>>>
>>>> > Am 22.06.2017 um 16:35 schrieb Álvaro Vilaplana García <
>>>> alvaro.vilaplana@gmail.com>:
>>>> >
>>>> > Hi,
>>>> >
>>>> > Please, can you help me with a problem? I summarise in the next
>>>> points, I hope is enough clear to approach some help.
>>>> >
>>>> >
>>>> > a) We have devices, each with its own ID, which we don’t have control
>>>> of
>>>> >
>>>> > b) These devices send messages, with an internally generated,
>>>> non-synced (amongst other devices) timestamp
>>>> >
>>>> > c) We want to detect when each devices may stop sending messages
>>>> >
>>>> > d) For that, we are using a ProcessFunction
>>>> >
>>>> > e) The devices put the messages in a Kafka topic, partitioned by ID.
>>>> >
>>>> > f) We are struggling with the ProcessFunction timeout feature:
>>>> >
>>>> > We cannot rely on real time (processing time), since the messages
>>>> from the devices may be delayed (even if their timestamp does not show
>>>> these delays) - so we rely on device timestamps instead.
>>>> > In our case an event comes in which: "Registers a timer to be fired
>>>> when the event time watermark passes the given time". The problem we have
>>>> is there are cases where we do not get an additional event after the first
>>>> event- which means that the original event timeouts are not triggered.
>>>> >
>>>> > As a side note we've seen in unit tests that flink seems to set a
>>>> watermark after the last event with a Long.MaxValue (9223372036854775807)
-
>>>> which hides the above problem.
>>>> >
>>>> > I am using Scala 2.11 /Flink versions 1.2.0
>>>> >
>>>> > Regards
>>>> > --
>>>> > ______________________________
>>>> >
>>>> > Álvaro Vilaplana García
>>>>
>>>>
>>>
>>>
>>> --
>>> ______________________________
>>>
>>> Álvaro Vilaplana García
>>>
>>>
>>>
>>
>>
>> --
>> ______________________________
>>
>> Álvaro Vilaplana García
>>
>
>
>
> --
> ______________________________
>
> Álvaro Vilaplana García
>
>
>


-- 
______________________________

Álvaro Vilaplana García

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