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From Nico Kruber <n...@data-artisans.com>
Subject Re: Inconsistent Results in Event Time based Sliding Window processing
Date Tue, 14 Feb 2017 14:28:51 GMT
Hmm, without any exceptions in the logs, I'd say that you may be on the right 
track with elements arriving with timestamps older than the last watermark.

You may play around with allowed lateness
https://ci.apache.org/projects/flink/flink-docs-release-1.2/dev/
windows.html#allowed-lateness
to see if this is actually the case.


Nico

On Tuesday, 14 February 2017 19:39:46 CET Sujit Sakre wrote:
> Hi Nico,
> 
> Thanks for the reply.
> 
> There are no exceptions or other errors in the job/task manager logs. I am
> running this example from Eclipse IDE with Kafka and Zookeeper running
> separately; in the console there are no errors shown while processing.
> Previously, we were missing some windows due to watermark exceeding the
> upcoming data timestamps, however, that is not the case anymore.
> 
> There is a working example. I will share the code and data with you
> separately on your email ID.
> 
> The results of processing are of three types:
> 1) Complete set of results is obtained without any missing calculations
> 2) A few windows (from 1 or 2 to more) are missing uniformly from
> calculations
> 3) In a particular window, only selective data is missing, whereas other
> data is processed accurately
> 
> These results are for the same set of inputs under same processing steps.
> 
> This is not predictable, and makes identification of error difficult, as
> sometimes it works i.e. results of pattern #1 and sometimes results of
> pattern #2 or #3 (#3 occurs less frequently, however it does take place.
> 
> 
> 
> 
> *Sujit Sakre*
> 
> Senior Technical Architect
> Tel: +91 22 6660 6600
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> 247
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> On 14 February 2017 at 18:55, Nico Kruber <nico@data-artisans.com> wrote:
> > Hi Sujit,
> > this does indeed sound strange and we are not aware of any data loss
> > issues.
> > Are there any exceptions or other errors in the job/taskmanager logs?
> > Do you have a minimal working example? Is it that whole windows are not
> > processed or just single items inside a window?
> > 
> > 
> > Nico
> > 
> > On Tuesday, 14 February 2017 16:57:31 CET Sujit Sakre wrote:
> > > Hi,
> > > 
> > > I have been using Flink 1.1.1 with Kafka 0.9 to process real time
> > 
> > streams.
> > 
> > > We have written our own Window Function and are processing data with
> > > Sliding Windows. We are using Event Time and use a custom watermark
> > > generator.
> > > 
> > > We select a particular window out of multiple sliding windows and
> > > process
> > > all items in the window in an iterative loop to increment counts of the
> > > items selected. After this we call the sink method to log the result in
> > > a
> > > database.
> > > 
> > > This is working fine most of the times, i.e. it produces the expected
> > > result most of the times. However there are situations when certain
> > 
> > windows
> > 
> > > are not processed (under same test conditions), this means the results
> > 
> > are
> > 
> > > less than expected i.e. the counts are less than expected. Sometimes,
> > 
> > items
> > 
> > > instead of certain windows not getting processed, certain items do not
> > 
> > get
> > 
> > > processed in the window. This is unpredictable.
> > > 
> > > I wish to know what could be the cause of this inconsistent behaviour.
> > 
> > How
> > 
> > > do we resolve it. We have integrated 1.2 and Kafka 0.10 now, the problem
> > > persists.
> > > 
> > > Please could you suggest about what the problem could be and how to
> > 
> > resolve
> > 
> > > this.
> > > 
> > > Many thanks.
> > > 
> > > 
> > > *Sujit Sakre*


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