001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *     http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    package org.apache.hadoop.hdfs.server.namenode;
019    
020    import java.io.Closeable;
021    import java.io.IOException;
022    
023    import org.apache.hadoop.classification.InterfaceAudience;
024    import org.apache.hadoop.classification.InterfaceStability;
025    import org.apache.hadoop.hdfs.server.common.Storage.FormatConfirmable;
026    import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
027    
028    /**
029     * A JournalManager is responsible for managing a single place of storing
030     * edit logs. It may correspond to multiple files, a backup node, etc.
031     * Even when the actual underlying storage is rolled, or failed and restored,
032     * each conceptual place of storage corresponds to exactly one instance of
033     * this class, which is created when the EditLog is first opened.
034     */
035    @InterfaceAudience.Private
036    @InterfaceStability.Evolving
037    public interface JournalManager extends Closeable, LogsPurgeable,
038                                            FormatConfirmable {
039    
040      /**
041       * Format the underlying storage, removing any previously
042       * stored data.
043       */
044      void format(NamespaceInfo ns) throws IOException;
045    
046      /**
047       * Begin writing to a new segment of the log stream, which starts at
048       * the given transaction ID.
049       */
050      EditLogOutputStream startLogSegment(long txId) throws IOException;
051    
052      /**
053       * Mark the log segment that spans from firstTxId to lastTxId
054       * as finalized and complete.
055       */
056      void finalizeLogSegment(long firstTxId, long lastTxId) throws IOException;
057    
058      /**
059       * Set the amount of memory that this stream should use to buffer edits
060       */
061      void setOutputBufferCapacity(int size);
062    
063      /**
064       * Recover segments which have not been finalized.
065       */
066      void recoverUnfinalizedSegments() throws IOException;
067    
068      /**
069       * Close the journal manager, freeing any resources it may hold.
070       */
071      @Override
072      void close() throws IOException;
073      
074      /** 
075       * Indicate that a journal is cannot be used to load a certain range of 
076       * edits.
077       * This exception occurs in the case of a gap in the transactions, or a
078       * corrupt edit file.
079       */
080      public static class CorruptionException extends IOException {
081        static final long serialVersionUID = -4687802717006172702L;
082        
083        public CorruptionException(String reason) {
084          super(reason);
085        }
086      }
087    }