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Posted to user@flink.apache.org by Paul Joireman <pa...@physiq.com> on 2016/10/24 15:02:16 UTC

Event time, watermarks and windows

Hi all,

The  event timestamp and watermarks documentation (v. 1.1)  https://ci.apache.org/projects/flink/flink-docs-release-1.1/apis/streaming/event_timestamps_watermarks.html states that

     The AssignerWithPeriodicWatermarks assigns timestamps and generates watermarks periodically (possibly depending on the stream elements, or purely
      based on processing time).

     The interval (every n milliseconds) in which the watermark will be generated is defined via ExecutionConfig.setAutoWatermarkInterval(...). Each time, the
     assigner's getCurrentWatermark() method will be called, and a new Watermark will be emitted, if the returned Watermark is non-null and larger than the
      previous Watermark.

It goes on to give an example of the BoundedOutOfOrdernessTimestampExtractor.   My question is that since the BoundedOutOfOrdernessTimestampExtractor is a sub-class of the AssignerWithPeriodicWatermarks is it necessary to call ExecutionConfig.setAutoWatermarkInterval(...) on the environment in order to actually generate watermarks or should they be generated "automatically" by the subsequent operators.

In other words, will an event time window still fire if this call (setAutoWatermarkInterval) is not present?

Regards,
Paul W Joireman

Re: Event time, watermarks and windows

Posted by Aljoscha Krettek <al...@apache.org>.

Hi,
the call to setAutoWatermarkInterval() is still necessary to activate the
watermark-generation mechanism. However, calling
setStreamTimeCharacteristic(EventTime) will also set a good default value
for the auto watermark interval.

Cheers,
Aljoscha

On Mon, 24 Oct 2016 at 17:02 Paul Joireman <pa...@physiq.com> wrote:

> Hi all,
>
> The  event timestamp and watermarks documentation (v. 1.1)
> https://ci.apache.org/projects/flink/flink-docs-release-1.1/apis/streaming/event_timestamps_watermarks.html states
> that
>
>      The AssignerWithPeriodicWatermarks assigns timestamps and generates
> watermarks periodically (possibly depending on the stream elements, or
> purely
>       based on processing time).
>
>      The interval (every n milliseconds) in which the watermark will be
> generated is defined via ExecutionConfig.setAutoWatermarkInterval(...).
> Each time, the
>      assigner’s getCurrentWatermark() method will be called, and a new
> Watermark will be emitted, if the returned Watermark is non-null and larger
> than the
>       previous Watermark.
>
> It goes on to give an example of the
> BoundedOutOfOrdernessTimestampExtractor.   My question is that since the BoundedOutOfOrdernessTimestampExtractor
> is a sub-class of the AssignerWithPeriodicWatermarks is it necessary to
> call ExecutionConfig.setAutoWatermarkInterval(...) on the environment in
> order to actually generate watermarks or should they be generated
> "automatically" by the subsequent operators.
>
> In other words, will an event time window still fire if this call
> (setAutoWatermarkInterval) is not present?
>
> Regards,
> Paul W Joireman
>