hadoop HashFirstResolver 源码
haddop HashFirstResolver 代码
文件路径：/hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/order/HashFirstResolver.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.order;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hdfs.server.federation.resolver.PathLocation;
/**
* Variation of HashResolver that only uses the first level of the path.
*/
public class HashFirstResolver extends HashResolver {
@Override
public String getFirstNamespace(final String path, final PathLocation loc) {
String srcPath = loc.getSourcePath();
String trimmedPath = trimPathToChild(path, srcPath);
LOG.debug("Only using the first part of the path: {} -> {}",
path, trimmedPath);
return super.getFirstNamespace(trimmedPath, loc);
}
/**
* Hash only up to the immediate child of the mount point. This prevents the
* need to create/maintain subtrees under each multi-destination mount point.
* Each child of a multi-destination mount is mapped to only one hash
* location.
* <p>
* Trims a path to at most the immediate child of a parent path. For example:
* <ul>
* <li>path = /a/b/c, parent = /a will be trimmed to /a/b.
* <li>path = /a/b, parent = /a/b will be trimmed to /a/b
* </ul>
*
* @param path The path to trim.
* @param parent The parent used to find the immediate child.
* @return Trimmed path.
*/
private static String trimPathToChild(String path, String parent) {
// Path is invalid or equal to the parent
if (path.length() <= parent.length()) {
return parent;
}
String remainder = path.substring(parent.length());
String[] components =
remainder.replaceFirst("^/", "").split(Path.SEPARATOR);
if (components.length > 0 && components[0].length() > 0) {
if (parent.endsWith(Path.SEPARATOR)) {
return parent + components[0];
} else {
return parent + Path.SEPARATOR + components[0];
}
} else {
return parent;
}
}
}
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