clear method on Window Trigger

[Soheil Pourbafrani]

Hi,

Can someone elaborate on when the clear method on class Trigger will be called and what is the duty of that? Also, I don't know what is the benefit of FIRE_AND_PURGE against FIRE and it's use case.

For example, in a scenario, if we have a count of 3 Window that also will trigger after a timeout if we FIRE window on timeout and after a while, a new data will be added to the data, will window be triggered for all data or not just for new late data? I guess in such such case we should use the FIRE_AND_PURGE.

[vino yang]

Hi Soheil,

Did you read the documentation about Flink Window/Trigger [1]? 

FIRE_AND_PURGE usually used to implement the count window. Flink provide a PurgingTrigger as a warper for other trigger to make those triggers can be purge. One of this class use case is count window[2][3].

About your example, you mean the window will triggered by count and time? if it is triggered by count condition we could use FIRE_AND_PURGE.

[1]: https://ci.apache.org/projects/flink/flink-docs-release-1.5/dev/stream/operators/windows.html#fire-and-purge

[2]: https://github.com/apache/flink/blob/master/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/datastream/DataStream.java#L765

[3]: https://github.com/apache/flink/blob/master/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/datastream/KeyedStream.java#L628

Thanks, vino.

2018-07-17 22:44 GMT+08:00 Soheil Pourbafrani <[hidden email]>:

Hi,

Can someone elaborate on when the clear method on class Trigger will be called and what is the duty of that? Also, I don't know what is the benefit of FIRE_AND_PURGE against FIRE and it's use case.

For example, in a scenario, if we have a count of 3 Window that also will trigger after a timeout if we FIRE window on timeout and after a while, a new data will be added to the data, will window be triggered for all data or not just for new late data? I guess in such such case we should use the FIRE_AND_PURGE.

[Hequn Cheng]

Hi Soheil,

The clear() method performs any action needed upon removal of the corresponding window. This is called when a window is purged. The differences between FIRE and FIRE_AND_PURGE is FIRE only trigger the computation while FIRE_AND_PURGE trigger the computation and clear the elements in the window afterwards.

As for your example, if you use FIRE, when the new data comes, the window is triggered for all data. Besides, some window functions can incrementally aggregate the elements for each window as they arrive, for example AggregateFunction and FoldFunction.

More details can be found here[1].

Best, Hequn

[1] https://ci.apache.org/projects/flink/flink-docs-master/dev/stream/operators/windows.html#windows

On Tue, Jul 17, 2018 at 10:44 PM, Soheil Pourbafrani <[hidden email]> wrote:

Hi,

Can someone elaborate on when the clear method on class Trigger will be called and what is the duty of that? Also, I don't know what is the benefit of FIRE_AND_PURGE against FIRE and it's use case.

For example, in a scenario, if we have a count of 3 Window that also will trigger after a timeout if we FIRE window on timeout and after a while, a new data will be added to the data, will window be triggered for all data or not just for new late data? I guess in such such case we should use the FIRE_AND_PURGE.