content: /*
   * 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.spark.streaming.util;
  
  import java.nio.ByteBuffer;
  import java.util.Iterator;
  
  /**
   * :: DeveloperApi ::
   *
   * This abstract class represents a write ahead log (aka journal) that is used by Spark Streaming
   * to save the received data (by receivers) and associated metadata to a reliable storage, so that
   * they can be recovered after driver failures. See the Spark documentation for more information
   * on how to plug in your own custom implementation of a write ahead log.
   */
  @org.apache.spark.annotation.DeveloperApi
  public abstract class WriteAheadLog {
    /**
     * Write the record to the log and return a record handle, which contains all the information
     * necessary to read back the written record. The time is used to the index the record,
     * such that it can be cleaned later. Note that implementations of this abstract class must
     * ensure that the written data is durable and readable (using the record handle) by the
     * time this function returns.
     */
    public abstract WriteAheadLogRecordHandle write(ByteBuffer record, long time);
  
    /**
     * Read a written record based on the given record handle.
     */
    public abstract ByteBuffer read(WriteAheadLogRecordHandle handle);
  
    /**
     * Read and return an iterator of all the records that have been written but not yet cleaned up.
     */
    public abstract Iterator<ByteBuffer> readAll();
  
    /**
     * Clean all the records that are older than the threshold time. It can wait for
     * the completion of the deletion.
     */
    public abstract void clean(long threshTime, boolean waitForCompletion);
  
    /**
     * Close this log and release any resources.
     */
    public abstract void close();
  }
  