hdfs/src/java/org/apache/hadoop/hdfs/server/common/Upgradeable.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.common;

import java.io.IOException;

import org.apache.hadoop.hdfs.server.protocol.UpgradeCommand;

/**
 * Common interface for distributed upgrade objects.
 * 
 * Each upgrade object corresponds to a layout version,
 * which is the latest version that should be upgraded using this object.
 * That is all components whose layout version is greater or equal to the
 * one returned by {@link #getVersion()} must be upgraded with this object.
 */
public interface Upgradeable extends Comparable<Upgradeable> {
  /**
   * Get the layout version of the upgrade object.
   * @return layout version
   */
  int getVersion();

  /**
   * Get the type of the software component, which this object is upgrading.
   * @return type
   */
  HdfsConstants.NodeType getType();

  /**
   * Description of the upgrade object for displaying.
   * @return description
   */
  String getDescription();

  /**
   * Upgrade status determines a percentage of the work done out of the total 
   * amount required by the upgrade.
   * 
   * 100% means that the upgrade is completed.
   * Any value < 100 means it is not complete.
   * 
   * The return value should provide at least 2 values, e.g. 0 and 100.
   * @return integer value in the range [0, 100].
   */
  short getUpgradeStatus();

  /**
   * Prepare for the upgrade.
   * E.g. initialize upgrade data structures and set status to 0.
   * 
   * Returns an upgrade command that is used for broadcasting to other cluster
   * components. 
   * E.g. name-node informs data-nodes that they must perform a distributed upgrade.
   * 
   * @return an UpgradeCommand for broadcasting.
   * @throws IOException
   */
  UpgradeCommand startUpgrade() throws IOException;

  /**
   * Complete upgrade.
   * E.g. cleanup upgrade data structures or write metadata to disk.
   * 
   * Returns an upgrade command that is used for broadcasting to other cluster
   * components. 
   * E.g. data-nodes inform the name-node that they completed the upgrade
   * while other data-nodes are still upgrading.
   * 
   * @throws IOException
   */
  UpgradeCommand completeUpgrade() throws IOException;

  /**
   * Get status report for the upgrade.
   * 
   * @param details true if upgradeStatus details need to be included, 
   *                false otherwise
   * @return {@link UpgradeStatusReport}
   * @throws IOException
   */
  UpgradeStatusReport getUpgradeStatusReport(boolean details) throws IOException;
}