com.twitter.heron.api.windowing.evictors.WatermarkTimeEvictionPolicy Maven / Gradle / Ivy
// Copyright 2017 Twitter. All rights reserved.
//
// Licensed 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,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* 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,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.twitter.heron.api.windowing.evictors;
import java.io.Serializable;
import com.twitter.heron.api.windowing.Event;
/**
* An eviction policy that evicts events based on time duration taking
* watermark time and event lag into account.
*/
public class WatermarkTimeEvictionPolicy extends TimeEvictionPolicy {
private final long lag;
/**
* Constructs a WatermarkTimeEvictionPolicy that evicts events older
* than the given window length in millis.
*
* @param windowLength the window length in milliseconds
*/
public WatermarkTimeEvictionPolicy(long windowLength) {
this(windowLength, Long.MAX_VALUE);
}
/**
* Constructs a WatermarkTimeEvictionPolicy that evicts events older
* than the given window length in millis. The lag parameter
* can be used in the case of event based ts to break the queue
* scan early.
*
* @param windowLength the window length in milliseconds
* @param lag the max event lag in milliseconds
*/
public WatermarkTimeEvictionPolicy(long windowLength, long lag) {
super(windowLength);
this.lag = lag;
}
/**
* {@inheritDoc}
*
* Keeps events with future ts in the queue for processing in the next
* window. If the ts difference is more than the lag, stops scanning
* the queue for the current window.
*/
@Override
public Action evict(Event event) {
if (evictionContext == null) {
//It is possible to get asked about eviction before we have a context, due to WindowManager
// .compactWindow.
//In this case we should hold on to all the events. When the first watermark is received,
// the context will be set,
//and the events will be reevaluated for eviction
return Action.STOP;
}
long referenceTime = evictionContext.getReferenceTime();
long diff = referenceTime - event.getTimestamp();
if (diff < -lag) {
return Action.STOP;
} else if (diff < 0) {
return Action.KEEP;
} else {
return super.evict(event);
}
}
@Override
public String toString() {
return "WatermarkTimeEvictionPolicy{" + "lag=" + lag + "} " + super.toString();
}
}