Hi Konstantin,
I finally nailed down the problem. :-)
The basis of the problem is the fact that there is a mismatch in the
parallelism of the Flink Kafka Consumer and the number of partitions in the
Kafka Stream. I would assume that in your case the Kafka Stream has 1
partition. This means, that only one of the parallel instances of the Flink
Kafka Consumer ever receives element, which in turn means that only one of the
parallel instances of the timestamp extractor ever receives elements. This
means that no watermarks get emitted for the other parallel instances which in
turn means that the watermark does not advance downstream because the watermark
at an operator is the minimum over all upstream watermarks. This explains why
ExampleTimestampExtractor1 only works in the case with parallelism=1.
The reason why ExampleTimestampExtractor2 works in all parallelism settings is
not very obvious. The secret is in this method:
@Override
public long getCurrentWatermark() {
return lastTimestamp - maxDelay;
}
In the parallel instances that never receive any element lastTimestamp is set
to Long.MIN_VALUE. So “lastTimestamp - maxDelay” is (Long.MAX_VALUE - maxDelay
(+1)). Now, because the watermark at an operator is always the minimum over all
watermarks from upstream operators the watermark at the window operator always
tracks the watermark of the parallel instance that receives elements.
I hope this helps, but please let me know if I should provide more explanation.
This is a very tricky topic.
Cheers,
Aljoscha
> On 29 Nov 2015, at 21:18, Konstantin Knauf <konstantin.kn...@tngtech.com>
> wrote:
>
> Hi Aljoscha,
>
> I have put together a gist [1] with two classes, a short processing
> pipeline, which shows the behavior and a data generator to write records
> into Kafka. I hope I remembered everything we discussed correctly.
>
> So basically in the example it works with "TimestampExtractor1" only for
> parallelism 1, with "TimestampExtractor2" it works regardless of the
> parallelism. Run from the IDE.
>
> Let me know if you need anything else.
>
> Cheers,
>
> Konstantin
>
> [1] https://gist.github.com/knaufk/d57b5c3c7db576f3350d
>
> On 25.11.2015 21:15, Konstantin Knauf wrote:
>> Hi Aljoscha,
>>
>> sure, will do. I have neither found a solution. I won't have time to put
>> a minimal example together before the weekend though.
>>
>> Cheers,
>>
>> Konstantin
>>
>> On 25.11.2015 19:10, Aljoscha Krettek wrote:
>>> Hi Konstantin,
>>> I still didn’t come up with an explanation for the behavior. Could you
>>> maybe send me example code (and example data if it is necessary to
>>> reproduce the problem.)? This would really help me pinpoint the problem.
>>>
>>> Cheers,
>>> Aljoscha
>>>> On 17 Nov 2015, at 21:42, Konstantin Knauf <konstantin.kn...@tngtech.com>
>>>> wrote:
>>>>
>>>> Hi Aljoscha,
>>>>
>>>> Are you sure? I am running the job from my IDE at the moment.
>>>>
>>>> If I set
>>>>
>>>> StreamExecutionEnvironment.setParallelism(1);
>>>>
>>>> I works with the old TimestampExtractor (returning Long.MIN_VALUE from
>>>> getCurrentWatermark() and emitting a watermark at every record)
>>>>
>>>> If I set
>>>>
>>>> StreamExecutionEnvironment.setParallelism(5);
>>>>
>>>> it does not work.
>>>>
>>>> So, if I understood you correctly, it is the opposite of what you were
>>>> expecting?!
>>>>
>>>> Cheers,
>>>>
>>>> Konstantin
>>>>
>>>>
>>>> On 17.11.2015 11:32, Aljoscha Krettek wrote:
>>>>> Hi,
>>>>> actually, the bug is more subtle. Normally, it is not a problem that the
>>>>> TimestampExtractor sometimes emits a watermark that is lower than the one
>>>>> before. (This is the result of the bug with Long.MIN_VALUE I mentioned
>>>>> before). The stream operators wait for watermarks from all upstream
>>>>> operators and only advance the watermark monotonically in lockstep with
>>>>> them. This way, the watermark cannot decrease at an operator.
>>>>>
>>>>> In your case, you have a topology with parallelism 1, I assume. In that
>>>>> case the operators are chained. (There is no separate operators but
>>>>> basically only one operator and element transmission happens in function
>>>>> calls). In this setting the watermarks are directly forwarded to
>>>>> operators without going through the logic I mentioned above.
>>>>>
>>>>> Cheers,
>>>>> Aljoscha
>>>>>> On 16 Nov 2015, at 18:13, Konstantin Knauf
>>>>>> <konstantin.kn...@tngtech.com> wrote:
>>>>>>
>>>>>> Hi Aljoscha,
>>>>>>
>>>>>> I changed the Timestamp Extraktor to save the lastSeenTimestamp and only
>>>>>> emit with getCurrentWatermark [1] as you suggested. So basically I do
>>>>>> the opposite than before (only watermarks per events vs only watermarks
>>>>>> per autowatermark). And now it works :). The question remains, why it
>>>>>> did not work before. As far as I see, it is an issue with the first
>>>>>> TimestmapExtractor itself?!
>>>>>>
>>>>>> Does getCurrentWatermark(..) somehow "overpower" the extracted
>>>>>> watermarks?
>>>>>>
>>>>>> Cheers,
>>>>>>
>>>>>> Konstantin
>>>>>>
>>>>>> [1]
>>>>>>
>>>>>> final private long maxDelay;
>>>>>> private long lastTimestamp = Long.MIN_VALUE;
>>>>>>
>>>>>> public PojoTimestampExtractor(long maxDelay) {
>>>>>> this.maxDelay = maxDelay;
>>>>>> }
>>>>>>
>>>>>> @Override
>>>>>> public long extractTimestamp(Pojo pojo, long l) {
>>>>>> lastTimestamp = pojo.getTime();
>>>>>> return pojo.getTime();
>>>>>> }
>>>>>>
>>>>>> @Override
>>>>>> public long extractWatermark(Pojo pojo, long l) {
>>>>>> return Long.MIN_VALUE;
>>>>>> }
>>>>>>
>>>>>> @Override
>>>>>> public long getCurrentWatermark() {
>>>>>> return lastTimestamp - maxDelay;
>>>>>> }
>>>>>>
>>>>>>
>>>>>> On 16.11.2015 13:37, Aljoscha Krettek wrote:
>>>>>>> Hi,
>>>>>>> yes, at your data-rate emitting a watermark for every element should
>>>>>>> not be a problem. It could become a problem with higher data-rates
>>>>>>> since the system can get overwhelmed if every element also generates a
>>>>>>> watermark. In that case I would suggest storing the lastest
>>>>>>> element-timestamp in an internal field and only emitting in
>>>>>>> getCurrentWatermark(), since then, then the watermark interval can be
>>>>>>> tunes using the auto-watermark interval setting.
>>>>>>>
>>>>>>> But that should not be the cause of the problem that you currently
>>>>>>> have. Would you maybe be willing to send me some (mock) example data
>>>>>>> and the code so that I can reproduce the problem and have a look at it?
>>>>>>> to aljoscha at apache.org.
>>>>>>>
>>>>>>> Cheers,
>>>>>>> Aljoscha
>>>>>>>> On 16 Nov 2015, at 13:05, Konstantin Knauf
>>>>>>>> <konstantin.kn...@tngtech.com> wrote:
>>>>>>>>
>>>>>>>> Hi Aljoscha,
>>>>>>>>
>>>>>>>> ok, now I at least understand, why it works with fromElements(...). For
>>>>>>>> the rest I am not so sure.
>>>>>>>>
>>>>>>>>> What this means in your case is that the watermark can only advance if
>>>>>>>> a new element arrives, because only then is the watermark updated.
>>>>>>>>
>>>>>>>> But new elements arrive all the time, about 50/s, or do you mean
>>>>>>>> something else?
>>>>>>>>
>>>>>>>> getCurrentWatermark returning Long.MIN_VALUE still seems to be an ok
>>>>>>>> choice, if i understand the semantics correctly. It just affects
>>>>>>>> watermarking in the absence of events, right?
>>>>>>>>
>>>>>>>> Cheers,
>>>>>>>>
>>>>>>>> Konstantin
>>>>>>>>
>>>>>>>>
>>>>>>>> On 16.11.2015 12:31, Aljoscha Krettek wrote:
>>>>>>>>> Hi,
>>>>>>>>> it could be what Gyula mentioned. Let me first go a bit into how the
>>>>>>>>> TimestampExtractor works internally.
>>>>>>>>>
>>>>>>>>> First, the timestamp extractor internally keeps the value of the last
>>>>>>>>> emitted watermark. Then, the semantics of the TimestampExtractor are
>>>>>>>>> as follows :
>>>>>>>>> - the result of extractTimestamp is taken and it replaces the
>>>>>>>>> internal timestamp of the element
>>>>>>>>> - if the result of extractWatermark is larger than the last watermark
>>>>>>>>> the new value is emitted as a watermark and the value is stored
>>>>>>>>> - getCurrentWatermark is called on the specified auto-watermark
>>>>>>>>> interval, if the returned value is larger than the last watermark it
>>>>>>>>> is emitted and stored as last watermark
>>>>>>>>>
>>>>>>>>> What this means in your case is that the watermark can only advance
>>>>>>>>> if a new element arrives, because only then is the watermark updated.
>>>>>>>>>
>>>>>>>>> The reason why you see results if you use fromElements is that the
>>>>>>>>> window-operator also emits all the windows that it currently has
>>>>>>>>> buffered if the program closes. This happens in the case of
>>>>>>>>> fromElements because only a finite number of elements is emitted,
>>>>>>>>> after which the source closes, thereby finishing the whole program.
>>>>>>>>>
>>>>>>>>> Cheers,
>>>>>>>>> Aljoscha
>>>>>>>>>> On 16 Nov 2015, at 10:42, Gyula Fóra <gyula.f...@gmail.com> wrote:
>>>>>>>>>>
>>>>>>>>>> Could this part of the extractor be the problem Aljoscha?
>>>>>>>>>>
>>>>>>>>>> @Override
>>>>>>>>>> public long getCurrentWatermark() {
>>>>>>>>>> return Long.MIN_VALUE;
>>>>>>>>>> }
>>>>>>>>>>
>>>>>>>>>> Gyula
>>>>>>>>>>
>>>>>>>>>> Konstantin Knauf <konstantin.kn...@tngtech.com> ezt írta (időpont:
>>>>>>>>>> 2015. nov. 16., H, 10:39):
>>>>>>>>>> Hi Aljoscha,
>>>>>>>>>>
>>>>>>>>>> thanks for your answer. Yes I am using the same
>>>>>>>>>> TimestampExtractor-Class.
>>>>>>>>>>
>>>>>>>>>> The timestamps look good to me. Here an example.
>>>>>>>>>>
>>>>>>>>>> {"time": 1447666537260, ...} And parsed:
>>>>>>>>>> 2015-11-16T10:35:37.260+01:00
>>>>>>>>>>
>>>>>>>>>> The order now is
>>>>>>>>>>
>>>>>>>>>> stream
>>>>>>>>>> .map(dummyMapper)
>>>>>>>>>> .assignTimestamps(...)
>>>>>>>>>> .timeWindow(...)
>>>>>>>>>>
>>>>>>>>>> Is there a way to print out the assigned timestamps after
>>>>>>>>>> stream.assignTimestamps(...)?
>>>>>>>>>>
>>>>>>>>>> Cheers,
>>>>>>>>>>
>>>>>>>>>> Konstantin
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On 16.11.2015 10:31, Aljoscha Krettek wrote:
>>>>>>>>>>> Hi,
>>>>>>>>>>> are you also using the timestamp extractor when you are using
>>>>>>>>>>> env.fromCollection().
>>>>>>>>>>>
>>>>>>>>>>> Could you maybe insert a dummy mapper after the Kafka source that
>>>>>>>>>>> just prints the element and forwards it? To see if the elements
>>>>>>>>>>> come with a good timestamp from Kafka.
>>>>>>>>>>>
>>>>>>>>>>> Cheers,
>>>>>>>>>>> Aljoscha
>>>>>>>>>>>> On 15 Nov 2015, at 22:55, Konstantin Knauf
>>>>>>>>>>>> <konstantin.kn...@tngtech.com> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>> Hi everyone,
>>>>>>>>>>>>
>>>>>>>>>>>> I have the following issue with Flink (0.10) and Kafka.
>>>>>>>>>>>>
>>>>>>>>>>>> I am using a very simple TimestampExtractor like [1], which just
>>>>>>>>>>>> extracts a millis timestamp from a POJO. In my streaming job, I
>>>>>>>>>>>> read in
>>>>>>>>>>>> these POJOs from Kafka using the FlinkKafkaConsumer082 like this:
>>>>>>>>>>>>
>>>>>>>>>>>> stream = env.addSource(new FlinkKafkaConsumer082<
>>>>>>>>>>>> (parameterTool.getRequired("topic"),
>>>>>>>>>>>> new AvroPojoDeserializationSchema(),
>>>>>>>>>>>> parameterTool.getProperties()))
>>>>>>>>>>>>
>>>>>>>>>>>> I have timestampEnabled() and the TimeCharacteristics are
>>>>>>>>>>>> EventTime,
>>>>>>>>>>>> AutoWatermarkIntervall is 500.
>>>>>>>>>>>>
>>>>>>>>>>>> The problem is, when I do something like:
>>>>>>>>>>>>
>>>>>>>>>>>> stream.assignTimestamps(new PojoTimestampExtractor(6000))
>>>>>>>>>>>> .timeWindowAll(Time.of(1, TimeUnit.SECONDS)
>>>>>>>>>>>> .sum(..)
>>>>>>>>>>>> .print()
>>>>>>>>>>>>
>>>>>>>>>>>> env.execute();
>>>>>>>>>>>>
>>>>>>>>>>>> the windows never get triggered.
>>>>>>>>>>>>
>>>>>>>>>>>> If I use ProcessingTime it works.
>>>>>>>>>>>> If I use env.fromCollection(...) instead of the KafkaSource it
>>>>>>>>>>>> works
>>>>>>>>>>>> with EventTime, too.
>>>>>>>>>>>>
>>>>>>>>>>>> Any ideas what I could be doing wrong are highly appreciated.
>>>>>>>>>>>>
>>>>>>>>>>>> Cheers,
>>>>>>>>>>>>
>>>>>>>>>>>> Konstantin
>>>>>>>>>>>>
>>>>>>>>>>>> [1]:
>>>>>>>>>>>>
>>>>>>>>>>>> public class PojoTimestampExtractor implements
>>>>>>>>>>>> TimestampExtractor<Pojo> {
>>>>>>>>>>>>
>>>>>>>>>>>> final private long maxDelay;
>>>>>>>>>>>>
>>>>>>>>>>>> public PojoTimestampExtractor(long maxDelay) {
>>>>>>>>>>>> this.maxDelay = maxDelay;
>>>>>>>>>>>> }
>>>>>>>>>>>>
>>>>>>>>>>>> @Override
>>>>>>>>>>>> public long extractTimestamp(Pojo fightEvent, long l) {
>>>>>>>>>>>> return pojo.getTime();
>>>>>>>>>>>> }
>>>>>>>>>>>>
>>>>>>>>>>>> @Override
>>>>>>>>>>>> public long extractWatermark(Pojo pojo, long l) {
>>>>>>>>>>>> return pojo.getTime() - maxDelay;
>>>>>>>>>>>> }
>>>>>>>>>>>>
>>>>>>>>>>>> @Override
>>>>>>>>>>>> public long getCurrentWatermark() {
>>>>>>>>>>>> return Long.MIN_VALUE;
>>>>>>>>>>>> }
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> --
>>>>>>>>>> Konstantin Knauf * konstantin.kn...@tngtech.com * +49-174-3413182
>>>>>>>>>> TNG Technology Consulting GmbH, Betastr. 13a, 85774 Unterföhring
>>>>>>>>>> Geschäftsführer: Henrik Klagges, Christoph Stock, Dr. Robert Dahlke
>>>>>>>>>> Sitz: Unterföhring * Amtsgericht München * HRB 135082
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>> --
>>>>>>>> Konstantin Knauf * konstantin.kn...@tngtech.com * +49-174-3413182
>>>>>>>> TNG Technology Consulting GmbH, Betastr. 13a, 85774 Unterföhring
>>>>>>>> Geschäftsführer: Henrik Klagges, Christoph Stock, Dr. Robert Dahlke
>>>>>>>> Sitz: Unterföhring * Amtsgericht München * HRB 135082
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> --
>>>>>> Konstantin Knauf * konstantin.kn...@tngtech.com * +49-174-3413182
>>>>>> TNG Technology Consulting GmbH, Betastr. 13a, 85774 Unterföhring
>>>>>> Geschäftsführer: Henrik Klagges, Christoph Stock, Dr. Robert Dahlke
>>>>>> Sitz: Unterföhring * Amtsgericht München * HRB 135082
>>>>>
>>>>>
>>>>
>>>> --
>>>> Konstantin Knauf * konstantin.kn...@tngtech.com * +49-174-3413182
>>>> TNG Technology Consulting GmbH, Betastr. 13a, 85774 Unterföhring
>>>> Geschäftsführer: Henrik Klagges, Christoph Stock, Dr. Robert Dahlke
>>>> Sitz: Unterföhring * Amtsgericht München * HRB 135082
>>>
>>>
>>
>
> --
> Konstantin Knauf * konstantin.kn...@tngtech.com * +49-174-3413182
> TNG Technology Consulting GmbH, Betastr. 13a, 85774 Unterföhring
> Geschäftsführer: Henrik Klagges, Christoph Stock, Dr. Robert Dahlke
> Sitz: Unterföhring * Amtsgericht München * HRB 135082
