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From Aljoscha Krettek <aljos...@apache.org>
Subject Re: Custom TimestampExtractor and FlinkKafkaConsumer082
Date Fri, 11 Dec 2015 17:06:51 GMT
The PRs are merged. :D
> On 11 Dec 2015, at 17:28, Stephan Ewen <sewen@apache.org> wrote:
> 
> A solution for that is in these two pull requests:
> 
> https://github.com/apache/flink/pull/1447
> 
> https://github.com/apache/flink/pull/1448
> 
> On Fri, Dec 4, 2015 at 10:21 PM, Robert Metzger <rmetzger@apache.org> wrote:
> I think we need to find a solution for this problem soon. 
> Another user is most likely affected: http://stackoverflow.com/q/34090808/568695
> 
> I've filed a JIRA for the problem: https://issues.apache.org/jira/browse/FLINK-3121
> 
> 
> On Mon, Nov 30, 2015 at 5:58 PM, Aljoscha Krettek <aljoscha@apache.org> wrote:
> Maybe. In the Kafka case we just need to ensure that parallel instances of the source
that know that they don’t have any partitions assigned to them emit Long.MAX_VALUE as a
watermark.
> 
> > On 30 Nov 2015, at 17:50, Gyula Fóra <gyula.fora@gmail.com> wrote:
> >
> > Hi,
> >
> > I think what we will need at some point for this are approximate whatermarks which
correlate event and ingest time.
> >
> > I think they have similar concepts in Millwheel/Dataflow.
> >
> > Cheers,
> > Gyula
> > On Mon, Nov 30, 2015 at 5:29 PM Aljoscha Krettek <aljoscha@apache.org> wrote:
> > Hi,
> > as an addition. I don’t have a solution yet, for the general problem of what happens
when a parallel instance of a source never receives elements. This watermark business is very
tricky...
> >
> > Cheers,
> > Aljoscha
> > > On 30 Nov 2015, at 17:20, Aljoscha Krettek <aljoscha@apache.org> wrote:
> > >
> > > 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.knauf@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.knauf@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.knauf@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.knauf@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.fora@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.knauf@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.knauf@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.knauf@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.knauf@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.knauf@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.knauf@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.knauf@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
> > >
> >
> 
> 
> 


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