Java tutorial
/** * 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.namenode; import java.util.HashMap; import java.util.Map; import java.util.SortedSet; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.hdfs.protocol.LayoutVersion; import org.apache.hadoop.hdfs.protocol.LayoutVersion.FeatureInfo; import org.apache.hadoop.hdfs.protocol.LayoutVersion.LayoutFeature; @InterfaceAudience.Private public class NameNodeLayoutVersion { /** Build layout version and corresponding feature matrix */ public final static Map<Integer, SortedSet<LayoutFeature>> FEATURES = new HashMap<Integer, SortedSet<LayoutFeature>>(); public static final int CURRENT_LAYOUT_VERSION = LayoutVersion.getCurrentLayoutVersion(Feature.values()); public static final int MINIMUM_COMPATIBLE_LAYOUT_VERSION = LayoutVersion .getMinimumCompatibleLayoutVersion(Feature.values()); static { LayoutVersion.updateMap(FEATURES, LayoutVersion.Feature.values()); LayoutVersion.updateMap(FEATURES, NameNodeLayoutVersion.Feature.values()); } public static SortedSet<LayoutFeature> getFeatures(int lv) { return FEATURES.get(lv); } public static boolean supports(final LayoutFeature f, final int lv) { return LayoutVersion.supports(FEATURES, f, lv); } /** * Enums for features that change the layout version. * <br><br> * To add a new layout version: * <ul> * <li>Define a new enum constant with a short enum name, the new layout version * and description of the added feature.</li> * <li>When adding a layout version with an ancestor that is not same as * its immediate predecessor, use the constructor where a specific ancestor * can be passed. * </li> * <li>Specify a minimum compatible layout version. The minimum compatible * layout version is the earliest prior version to which a downgrade is * possible after initiating rolling upgrade. If the feature cannot satisfy * compatibility with any prior version, then set its minimum compatible * lqyout version to itself to indicate that downgrade is impossible. * Satisfying compatibility might require adding logic to the new feature to * reject operations or handle them differently while rolling upgrade is in * progress. In general, it's possible to satisfy compatiblity for downgrade * if the new feature just involves adding new edit log ops. Deeper * structural changes, such as changing the way we place files in the metadata * directories, might be incompatible. Feature implementations should strive * for compatibility, because it's in the best interest of our users to * support downgrade. * </ul> */ public enum Feature implements LayoutFeature { ROLLING_UPGRADE(-55, -53, -55, "Support rolling upgrade", false), EDITLOG_LENGTH(-56, -56, "Add length field to every edit log op"), XATTRS(-57, -57, "Extended attributes"), CREATE_OVERWRITE( -58, -58, "Use single editlog record for " + "creating file with overwrite"), XATTRS_NAMESPACE_EXT( -59, -59, "Increase number of xattr namespaces"), BLOCK_STORAGE_POLICY(-60, -60, "Block Storage policy"), TRUNCATE(-61, -61, "Truncate"), APPEND_NEW_BLOCK( -62, -61, "Support appending to new block"), QUOTA_BY_STORAGE_TYPE(-63, -61, "Support quota for specific storage types"), ERASURE_CODING( -64, -61, "Support erasure coding"), EXPANDED_STRING_TABLE( -65, -61, "Support expanded string table in fsimage"); private final FeatureInfo info; /** * Feature that is added at layout version {@code lv} - 1. * @param lv new layout version with the addition of this feature * @param minCompatLV minimium compatible layout version * @param description description of the feature */ Feature(final int lv, int minCompatLV, final String description) { this(lv, lv + 1, minCompatLV, description, false); } /** * NameNode feature that is added at layout version {@code ancestoryLV}. * @param lv new layout version with the addition of this feature * @param ancestorLV layout version from which the new lv is derived from. * @param minCompatLV minimum compatible layout version * @param description description of the feature * @param reserved true when this is a layout version reserved for previous * versions * @param features set of features that are to be enabled for this version */ Feature(final int lv, final int ancestorLV, int minCompatLV, final String description, boolean reserved, Feature... features) { info = new FeatureInfo(lv, ancestorLV, minCompatLV, description, reserved, features); } @Override public FeatureInfo getInfo() { return info; } } }