Understanding windowed aggregations

[Jon Yeargers <jo...@cedexis.com>]

Im creating aggregated values as follows:

kStream.groupByKey.aggregate( ... ,TimeWindows.of(20 * 60 *
1000L).advanceBy(60 * 1000L), ...);

As I process each aggregate Im storing the current system clock time in the
aggregated record.

Im watching the aggregates come through with a subsequent '.forEach()'.

My assumption would be that an aggregate would occur when the time for a
new value falls between the start and end of a given window. Instead Im
seeing all values happen outside the expected range (Windowed.start() ->
Windowed.end())

Am I really confused about how this works?

Re: Understanding windowed aggregations

["Matthias J. Sax" <ma...@confluent.io>]

By default, Kafka Streams uses *event-time* and not *system-time* to
assign records to windows. That's why you observe this.

Please have look here and follow up if you have further question:

http://docs.confluent.io/current/streams/concepts.html#time


-Matthias


On 12/5/16 8:42 AM, Jon Yeargers wrote:
> Im creating aggregated values as follows:
> 
> kStream.groupByKey.aggregate( ... ,TimeWindows.of(20 * 60 *
> 1000L).advanceBy(60 * 1000L), ...);
> 
> As I process each aggregate Im storing the current system clock time in the
> aggregated record.
> 
> Im watching the aggregates come through with a subsequent '.forEach()'.
> 
> My assumption would be that an aggregate would occur when the time for a
> new value falls between the start and end of a given window. Instead Im
> seeing all values happen outside the expected range (Windowed.start() ->
> Windowed.end())
> 
> Am I really confused about how this works?
>