org.apache.flink.streaming.api.functions.AssignerWithPeriodicWatermarks Maven / Gradle / Ivy
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* to you under the Apache License, Version 2.0 (the
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* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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*/
package org.apache.flink.streaming.api.functions;
import org.apache.flink.api.common.ExecutionConfig;
import org.apache.flink.streaming.api.watermark.Watermark;
import javax.annotation.Nullable;
/**
* The {@code AssignerWithPeriodicWatermarks} assigns 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 {@code i}
* milliseconds (configured via {@link ExecutionConfig#getAutoWatermarkInterval()}), the system will
* call the {@link #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 {@link #getCurrentWatermark()} method less often than every {@code i}
* milliseconds, if no new elements arrived since the last call to the method.
*
*
Timestamps and watermarks are defined as {@code longs} that represent the milliseconds since
* the Epoch (midnight, January 1, 1970 UTC). A watermark with a certain value {@code t} indicates
* that no elements with event timestamps {@code x}, where {@code x} is lower or equal to {@code t},
* will occur any more.
*
* @param The type of the elements to which this assigner assigns timestamps.
* @see org.apache.flink.streaming.api.watermark.Watermark
*/
@Deprecated
public interface AssignerWithPeriodicWatermarks extends TimestampAssigner {
/**
* Returns the current watermark. This method is periodically called by the system to retrieve
* the current watermark. The method may return {@code null} to 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 depends on {@link
* ExecutionConfig#getAutoWatermarkInterval()}.
*
* @see org.apache.flink.streaming.api.watermark.Watermark
* @see ExecutionConfig#getAutoWatermarkInterval()
* @return {@code Null}, if no watermark should be emitted, or the next watermark to emit.
*/
@Nullable
Watermark getCurrentWatermark();
}