/**
* Copyright 2016 Yahoo Inc.
*
* 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.
*/
package com.yahoo.pulsar.broker.loadbalance.impl;
import java.util.Map;
import java.util.Random;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.google.common.collect.Iterables;
import com.google.common.collect.Multimap;
import com.yahoo.pulsar.broker.loadbalance.PlacementStrategy;
import com.yahoo.pulsar.broker.loadbalance.ResourceUnit;
/**
*
* This class implements PlacementStrategy based on Weighted Round Robin Algorithm.
*/
public class WRRPlacementStrategy implements PlacementStrategy {
private static final Logger log = LoggerFactory.getLogger(WRRPlacementStrategy.class);
private final Random rand = new Random();
/**
* <code>
* Function : getByWeightedRoundRobin
* returns ResourceUnit selected by WRR algorithm based on available resource on RU
* ^
* |
* |
* |
* | | | | |
* | | | | |
* | Broker 2 | Broker 3 | Broker 1 | B4 |
* | | | | |
* +----------------+------------------------+--------------------------------+--------->
* 0 20 50 90 100
*
* This is weighted Round robin, we calculate weight based on availability of resources;
* total availability is taken as a full range then each broker is given range based on
* its resource availability, if the number generated within total range happens to be in
* broker's range, that broker is selected
* </code>
*/
public ResourceUnit findBrokerForPlacement(Multimap<Long, ResourceUnit> finalCandidates) {
if (finalCandidates.isEmpty()) {
return null;
}
log.debug("Total Final Candidates selected - [{}]", finalCandidates.size());
int totalAvailability = 0;
for (Map.Entry<Long, ResourceUnit> candidateOwner : finalCandidates.entries()) {
totalAvailability += candidateOwner.getKey().intValue();
}
ResourceUnit selectedRU = null;
if (totalAvailability <= 0) {
// todo: this means all the brokers are overloaded and we can't assign this namespace to any broker
// for now, pick anyone and return that one, because when we don't have ranking we put O for each broker
return Iterables.get(finalCandidates.get(0L), rand.nextInt(finalCandidates.size()));
}
int weightedSelector = rand.nextInt(totalAvailability);
log.debug("Generated Weighted Selector Number - [{}] ", weightedSelector);
int weightRangeSoFar = 0;
for (Map.Entry<Long, ResourceUnit> candidateOwner : finalCandidates.entries()) {
weightRangeSoFar += candidateOwner.getKey();
if (weightedSelector < weightRangeSoFar) {
selectedRU = candidateOwner.getValue();
log.debug(" Weighted Round Robin Selected RU - [{}]", candidateOwner.getValue().getResourceId());
break;
}
}
return selectedRU;
}
}