flink-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Jack Huang <jackhu...@mz.com>
Subject Re: Cannot use WindowedStream.fold with EventTimeSessionWindows
Date Wed, 17 Aug 2016 19:07:03 GMT
Hi Till,

The session I am dealing with does not have a reliable "end-of-session"
event. It could stop sending events all of sudden or it could keep sending
events forever. I need to be able to determine when a session expire due to
inactivity or to kill off a session if it lives longer than it should.
Therefore I need to perform incremental aggregation.

If I can assume ascending timestamp for the incoming events, would there be
a workaround?

Thanks,
Jack



On Wed, Aug 17, 2016 at 2:17 AM, Till Rohrmann <trohrmann@apache.org> wrote:

> Hi Jack,
>
> the problem with session windows and a fold operation, which is an
> incremental operation, is that you don't have a way to combine partial
> folds when merigng windows. As a workaround you have to specify a window
> function where you get an iterator over all your window elements and then
> perform the fold manually in the window function.
>
> Cheers,
> Till
>
> On Wed, Aug 17, 2016 at 3:21 AM, Jack Huang <jackhuang@mz.com> wrote:
>
>> Hi all,
>>
>> I want to window a series of events using SessionWindow and use fold
>> function to incrementally aggregate the result.
>>
>> events
>>     .keyBy(_.id)
>>     .window(EventTimeSessionWindows.withGap(Time.minutes(1)))
>>     .fold(new Session)(eventFolder)
>>
>> ​
>> However I get
>>
>> java.lang.UnsupportedOperationException: Fold cannot be used with a merging WindowAssigner.
>>
>> ​
>>
>> Does anyone have a workaround?
>>
>>
>>
>> Thanks,
>> Jack
>>
>>
>>
>>
>

Mime
View raw message