hadoop NamenodePriorityComparator 源码
haddop NamenodePriorityComparator 代码
文件路径：/hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/NamenodePriorityComparator.java
/**
* 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 org.apache.hadoop.hdfs.server.federation.resolver;
import java.io.Serializable;
import java.util.Comparator;
/**
* Compares NNs in the same namespace and prioritizes by their status. The
* priorities are:
* <ul>
* <li>ACTIVE
* <li>STANDBY
* <li>UNAVAILABLE
* </ul>
* When two NNs have the same state, the last modification date is the tie
* breaker, newest has priority. Expired NNs are excluded.
*/
public class NamenodePriorityComparator
implements Comparator<FederationNamenodeContext>, Serializable {
private static final long serialVersionUID = 2304924292036293331L;
@Override
public int compare(FederationNamenodeContext o1,
FederationNamenodeContext o2) {
FederationNamenodeServiceState state1 = o1.getState();
FederationNamenodeServiceState state2 = o2.getState();
if (state1 == state2) {
// Both have the same state, use mode dates
return compareModDates(o1, o2);
} else {
// Enum is ordered by priority
return state1.compareTo(state2);
}
}
/**
* Compare the modification dates.
*
* @param o1 Context 1.
* @param o2 Context 2.
* @return Comparison between dates.
*/
private int compareModDates(FederationNamenodeContext o1,
FederationNamenodeContext o2) {
// Reverse sort, lowest position is highest priority.
return (int) (o2.getDateModified() - o1.getDateModified());
}
}
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