T- The type of the elements to which this assigner assigns timestamps.
public interface AssignerWithPeriodicWatermarks<T> extends TimestampAssigner<T>
AssignerWithPeriodicWatermarksassigns event time timestamps to elements, and generates low watermarks that signal event time progress within the stream. These timestamps and watermarks are used by functions and operators that operate on event time, for example event time windows.
Use this class to generate watermarks in a periodical interval.
At most every
i milliseconds (configured via
ExecutionConfig.getAutoWatermarkInterval()), the system will call the
getCurrentWatermark() method to probe for the next watermark value.
The system will generate a new watermark, if the probed value is non-null
and has a timestamp larger than that of the previous watermark (to preserve
the contract of ascending watermarks).
The system may call the
getCurrentWatermark() method less often than every
i milliseconds, if no new elements arrived since the last call to the
Timestamps and watermarks are defined as
longs that represent the
milliseconds since the Epoch (midnight, January 1, 1970 UTC).
A watermark with a certain value
t indicates that no elements with event
x is lower or equal to
t, will occur any more.
nullto indicate that no new Watermark is available.
The returned watermark will be emitted only if it is non-null and its timestamp is larger than that of the previously emitted watermark (to preserve the contract of ascending watermarks). If the current watermark is still identical to the previous one, no progress in event time has happened since the previous call to this method. If a null value is returned, or the timestamp of the returned watermark is smaller than that of the last emitted one, then no new watermark will be generated.
The interval in which this method is called and Watermarks are generated
Copyright © 2014–2018 The Apache Software Foundation. All rights reserved.