org.apache.flink.streaming.api.functions.timestamps.BoundedOutOfOrdernessTimestampExtractor Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
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* distributed with this work for additional information
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* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* 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.timestamps;
import org.apache.flink.streaming.api.functions.AssignerWithPeriodicWatermarks;
import org.apache.flink.streaming.api.watermark.Watermark;
import org.apache.flink.streaming.api.windowing.time.Time;
/**
* This is a {@link AssignerWithPeriodicWatermarks} used to emit Watermarks that lag behind the element with
* the maximum timestamp (in event time) seen so far by a fixed amount of time, t_late. This can
* help reduce the number of elements that are ignored due to lateness when computing the final result for a
* given window, in the case where we know that elements arrive no later than t_late units of time
* after the watermark that signals that the system event-time has advanced past their (event-time) timestamp.
* */
public abstract class BoundedOutOfOrdernessTimestampExtractor implements AssignerWithPeriodicWatermarks {
private static final long serialVersionUID = 1L;
/** The current maximum timestamp seen so far. */
private long currentMaxTimestamp;
/** The timestamp of the last emitted watermark. */
private long lastEmittedWatermark = Long.MIN_VALUE;
/**
* The (fixed) interval between the maximum seen timestamp seen in the records
* and that of the watermark to be emitted.
*/
private final long maxOutOfOrderness;
public BoundedOutOfOrdernessTimestampExtractor(Time maxOutOfOrderness) {
if (maxOutOfOrderness.toMilliseconds() < 0) {
throw new RuntimeException("Tried to set the maximum allowed " +
"lateness to " + maxOutOfOrderness + ". This parameter cannot be negative.");
}
this.maxOutOfOrderness = maxOutOfOrderness.toMilliseconds();
this.currentMaxTimestamp = Long.MIN_VALUE + this.maxOutOfOrderness;
}
public long getMaxOutOfOrdernessInMillis() {
return maxOutOfOrderness;
}
/**
* Extracts the timestamp from the given element.
*
* @param element The element that the timestamp is extracted from.
* @return The new timestamp.
*/
public abstract long extractTimestamp(T element);
@Override
public final Watermark getCurrentWatermark() {
// this guarantees that the watermark never goes backwards.
long potentialWM = currentMaxTimestamp - maxOutOfOrderness;
if (potentialWM >= lastEmittedWatermark) {
lastEmittedWatermark = potentialWM;
}
return new Watermark(lastEmittedWatermark);
}
@Override
public final long extractTimestamp(T element, long previousElementTimestamp) {
long timestamp = extractTimestamp(element);
if (timestamp > currentMaxTimestamp) {
currentMaxTimestamp = timestamp;
}
return timestamp;
}
}