/**
 * 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.io;

import java.io.*;
import java.util.*;
import java.net.InetAddress;
import java.net.URI;
import java.net.URISyntaxException;
import java.rmi.server.UID;
import java.security.MessageDigest;
import org.apache.commons.logging.*;
import org.apache.hadoop.fs.*;
import org.apache.hadoop.io.compress.CompressionCodec;
import org.apache.hadoop.io.compress.CompressionInputStream;
import org.apache.hadoop.io.compress.CompressionOutputStream;
import org.apache.hadoop.io.compress.DefaultCodec;
import org.apache.hadoop.io.compress.GzipCodec;
import org.apache.hadoop.io.compress.zlib.ZlibFactory;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.util.Progressable;
import org.apache.hadoop.util.Progress;
import org.apache.hadoop.util.ReflectionUtils;
import org.apache.hadoop.util.NativeCodeLoader;
import org.apache.hadoop.util.MergeSort;
import org.apache.hadoop.util.PriorityQueue;

/** Support for flat files of binary key/value pairs. */
public class SequenceFile {
  public static final Log LOG =
    LogFactory.getLog("org.apache.hadoop.io.SequenceFile");

  private SequenceFile() {}                         // no public ctor

  private static final byte BLOCK_COMPRESS_VERSION = (byte)4;
  private static final byte CUSTOM_COMPRESS_VERSION = (byte)5;
  private static final byte VERSION_WITH_METADATA = (byte)6;
  private static byte[] VERSION = new byte[] {
    (byte)'S', (byte)'E', (byte)'Q', VERSION_WITH_METADATA
  };

  private static final int SYNC_ESCAPE = -1;      // "length" of sync entries
  private static final int SYNC_HASH_SIZE = 16;   // number of bytes in hash 
  private static final int SYNC_SIZE = 4+SYNC_HASH_SIZE; // escape + hash

  /** The number of bytes between sync points.*/
  public static final int SYNC_INTERVAL = 100*SYNC_SIZE; 

  /** The type of compression.
   * @see SequenceFile.Writer
   */
  public static enum CompressionType {
    /** Do not compress records. */
    NONE, 
    /** Compress values only, each separately. */
    RECORD,
    /** Compress sequences of records together in blocks. */
    BLOCK
  }

  /**
   * Get the compression type for the reduce outputs
   * @param job the job config to look in
   * @return the kind of compression to use
   */
  static public CompressionType getCompressionType(Configuration job) {
    String name = job.get("io.seqfile.compression.type");
    return name == null ? CompressionType.RECORD : 
      CompressionType.valueOf(name);
  }
  
  /**
   * Set the compression type for sequence files.
   * @param job the configuration to modify
   * @param val the new compression type (none, block, record)
   */
  static public void setCompressionType(Configuration job, 
                                        CompressionType val) {
    job.set("io.seqfile.compression.type", val.toString());
  }
    
  /**
   * Construct the preferred type of SequenceFile Writer.
   * @param fs The configured filesystem. 
   * @param conf The configuration.
   * @param name The name of the file. 
   * @param keyClass The 'key' type.
   * @param valClass The 'value' type.
   * @return Returns the handle to the constructed SequenceFile Writer.
   * @throws IOException
   */
  public static Writer 
    createWriter(FileSystem fs, Configuration conf, Path name, 
                 Class keyClass, Class valClass) 
    throws IOException {
    return createWriter(fs, conf, name, keyClass, valClass,
                        getCompressionType(conf));
  }
  
  /**
   * Construct the preferred type of SequenceFile Writer.
   * @param fs The configured filesystem. 
   * @param conf The configuration.
   * @param name The name of the file. 
   * @param keyClass The 'key' type.
   * @param valClass The 'value' type.
   * @param compressionType The compression type.
   * @return Returns the handle to the constructed SequenceFile Writer.
   * @throws IOException
   */
  public static Writer 
    createWriter(FileSystem fs, Configuration conf, Path name, 
                 Class keyClass, Class valClass, CompressionType compressionType) 
    throws IOException {
    Writer writer = null;
    
    if (compressionType == CompressionType.NONE) {
      writer = new Writer(fs, conf, name, keyClass, valClass, null, new Metadata());
    } else if (compressionType == CompressionType.RECORD) {
      writer = new RecordCompressWriter(fs, conf, name, keyClass, valClass, 
                                        new DefaultCodec());
    } else if (compressionType == CompressionType.BLOCK){
      writer = new BlockCompressWriter(fs, conf, name, keyClass, valClass, 
                                       new DefaultCodec());
    }
    
    return writer;
  }
  
  /**
   * Construct the preferred type of SequenceFile Writer.
   * @param fs The configured filesystem. 
   * @param conf The configuration.
   * @param name The name of the file. 
   * @param keyClass The 'key' type.
   * @param valClass The 'value' type.
   * @param compressionType The compression type.
   * @param progress The Progressable object to track progress.
   * @return Returns the handle to the constructed SequenceFile Writer.
   * @throws IOException
   */
  public static Writer
    createWriter(FileSystem fs, Configuration conf, Path name, 
                 Class keyClass, Class valClass, CompressionType compressionType,
                 Progressable progress) throws IOException {
    Writer writer = null;
    
    if (compressionType == CompressionType.NONE) {
      writer = new Writer(fs, conf, name, keyClass, valClass, progress, new Metadata()); 
    } else if (compressionType == CompressionType.RECORD) {
      writer = new RecordCompressWriter(fs, conf, name, 
                                        keyClass, valClass, new DefaultCodec(), progress, new Metadata());
    } else if (compressionType == CompressionType.BLOCK){
      writer = new BlockCompressWriter(fs, conf, name, 
                                       keyClass, valClass, new DefaultCodec(), progress, new Metadata());
    }
    
    return writer;
  }

  /**
   * Construct the preferred type of SequenceFile Writer.
   * @param fs The configured filesystem. 
   * @param conf The configuration.
   * @param name The name of the file. 
   * @param keyClass The 'key' type.
   * @param valClass The 'value' type.
   * @param compressionType The compression type.
   * @param codec The compression codec.
   * @return Returns the handle to the constructed SequenceFile Writer.
   * @throws IOException
   */
  public static Writer 
    createWriter(FileSystem fs, Configuration conf, Path name, 
                 Class keyClass, Class valClass, 
                 CompressionType compressionType, CompressionCodec codec) 
    throws IOException {
    if ((codec instanceof GzipCodec) && 
        !NativeCodeLoader.isNativeCodeLoaded() && 
        !ZlibFactory.isNativeZlibLoaded()) {
      throw new IllegalArgumentException("SequenceFile doesn't work with " +
                                         "GzipCodec without native-hadoop code!");
    }
    
    Writer writer = null;
    
    if (compressionType == CompressionType.NONE) {
      writer = new Writer(fs, conf, name, keyClass, valClass); 
    } else if (compressionType == CompressionType.RECORD) {
      writer = new RecordCompressWriter(fs, conf, name, keyClass, valClass, 
                                        codec);
    } else if (compressionType == CompressionType.BLOCK){
      writer = new BlockCompressWriter(fs, conf, name, keyClass, valClass, 
                                       codec);
    }
    
    return writer;
  }
  
  /**
   * Construct the preferred type of SequenceFile Writer.
   * @param fs The configured filesystem. 
   * @param conf The configuration.
   * @param name The name of the file. 
   * @param keyClass The 'key' type.
   * @param valClass The 'value' type.
   * @param compressionType The compression type.
   * @param codec The compression codec.
   * @param progress The Progressable object to track progress.
   * @param metadata The metadata of the file.
   * @return Returns the handle to the constructed SequenceFile Writer.
   * @throws IOException
   */
  public static Writer
    createWriter(FileSystem fs, Configuration conf, Path name, 
                 Class keyClass, Class valClass, 
                 CompressionType compressionType, CompressionCodec codec,
                 Progressable progress, Metadata metadata) throws IOException {
    if ((codec instanceof GzipCodec) && 
        !NativeCodeLoader.isNativeCodeLoaded() && 
        !ZlibFactory.isNativeZlibLoaded()) {
      throw new IllegalArgumentException("SequenceFile doesn't work with " +
                                         "GzipCodec without native-hadoop code!");
    }
    
    Writer writer = null;
    
    if (compressionType == CompressionType.NONE) {
      writer = new Writer(fs, conf, name, keyClass, valClass, progress, metadata);
    } else if (compressionType == CompressionType.RECORD) {
      writer = new RecordCompressWriter(fs, conf, name, 
                                        keyClass, valClass, codec, progress, metadata);
    } else if (compressionType == CompressionType.BLOCK){
      writer = new BlockCompressWriter(fs, conf, name, 
                                       keyClass, valClass, codec, progress, metadata);
    }
    
    return writer;
  }
  
  /**
   * Construct the preferred type of SequenceFile Writer.
   * @param fs The configured filesystem. 
   * @param conf The configuration.
   * @param name The name of the file. 
   * @param keyClass The 'key' type.
   * @param valClass The 'value' type.
   * @param compressionType The compression type.
   * @param codec The compression codec.
   * @param progress The Progressable object to track progress.
   * @return Returns the handle to the constructed SequenceFile Writer.
   * @throws IOException
   */
  public static Writer
    createWriter(FileSystem fs, Configuration conf, Path name, 
                 Class keyClass, Class valClass, 
                 CompressionType compressionType, CompressionCodec codec,
                 Progressable progress) throws IOException {
    Writer writer = createWriter(fs, conf, name, keyClass, valClass, 
                                 compressionType, codec, progress, new Metadata());
    return writer;
  }

  /**
   * Construct the preferred type of 'raw' SequenceFile Writer.
   * @param out The stream on top which the writer is to be constructed.
   * @param keyClass The 'key' type.
   * @param valClass The 'value' type.
   * @param compress Compress data?
   * @param blockCompress Compress blocks?
   * @param metadata The metadata of the file.
   * @return Returns the handle to the constructed SequenceFile Writer.
   * @throws IOException
   */
  private static Writer
    createWriter(Configuration conf, FSDataOutputStream out, 
                 Class keyClass, Class valClass, boolean compress, boolean blockCompress,
                 CompressionCodec codec, Metadata metadata)
    throws IOException {
    if ((codec instanceof GzipCodec) && 
        !NativeCodeLoader.isNativeCodeLoaded() && 
        !ZlibFactory.isNativeZlibLoaded()) {
      throw new IllegalArgumentException("SequenceFile doesn't work with " +
                                         "GzipCodec without native-hadoop code!");
    }

    Writer writer = null;

    if (!compress) {
      writer = new Writer(conf, out, keyClass, valClass, metadata);
    } else if (compress && !blockCompress) {
      writer = new RecordCompressWriter(conf, out, keyClass, valClass, codec, metadata);
    } else {
      writer = new BlockCompressWriter(conf, out, keyClass, valClass, codec, metadata);
    }
    
    return writer;
  }

  /**
   * Construct the preferred type of 'raw' SequenceFile Writer.
   * @param out The stream on top which the writer is to be constructed.
   * @param keyClass The 'key' type.
   * @param valClass The 'value' type.
   * @param compress Compress data?
   * @param blockCompress Compress blocks?
   * @return Returns the handle to the constructed SequenceFile Writer.
   * @throws IOException
   */
  private static Writer
    createWriter(Configuration conf, FSDataOutputStream out, 
                 Class keyClass, Class valClass, boolean compress, boolean blockCompress,
                 CompressionCodec codec)
    throws IOException {
    Writer writer = createWriter(conf, out, keyClass, valClass, compress, 
                                 blockCompress, codec, new Metadata());
    return writer;
  }

  
  /**
   * Construct the preferred type of 'raw' SequenceFile Writer.
   * @param conf The configuration.
   * @param out The stream on top which the writer is to be constructed.
   * @param keyClass The 'key' type.
   * @param valClass The 'value' type.
   * @param compressionType The compression type.
   * @param codec The compression codec.
   * @param metadata The metadata of the file.
   * @return Returns the handle to the constructed SequenceFile Writer.
   * @throws IOException
   */
  public static Writer
    createWriter(Configuration conf, FSDataOutputStream out, 
                 Class keyClass, Class valClass, CompressionType compressionType,
                 CompressionCodec codec, Metadata metadata)
    throws IOException {
    if ((codec instanceof GzipCodec) && 
        !NativeCodeLoader.isNativeCodeLoaded() && 
        !ZlibFactory.isNativeZlibLoaded()) {
      throw new IllegalArgumentException("SequenceFile doesn't work with " +
                                         "GzipCodec without native-hadoop code!");
    }

    Writer writer = null;

    if (compressionType == CompressionType.NONE) {
      writer = new Writer(conf, out, keyClass, valClass, metadata);
    } else if (compressionType == CompressionType.RECORD) {
      writer = new RecordCompressWriter(conf, out, keyClass, valClass, codec, metadata);
    } else if (compressionType == CompressionType.BLOCK){
      writer = new BlockCompressWriter(conf, out, keyClass, valClass, codec, metadata);
    }
    
    return writer;
  }
  
  /**
   * Construct the preferred type of 'raw' SequenceFile Writer.
   * @param conf The configuration.
   * @param out The stream on top which the writer is to be constructed.
   * @param keyClass The 'key' type.
   * @param valClass The 'value' type.
   * @param compressionType The compression type.
   * @param codec The compression codec.
   * @return Returns the handle to the constructed SequenceFile Writer.
   * @throws IOException
   */
  public static Writer
    createWriter(Configuration conf, FSDataOutputStream out, 
                 Class keyClass, Class valClass, CompressionType compressionType,
                 CompressionCodec codec)
    throws IOException {
    Writer writer = createWriter(conf, out, keyClass, valClass, compressionType,
                                 codec, new Metadata());
    return writer;
  }
  

  /** The interface to 'raw' values of SequenceFiles. */
  public static interface ValueBytes {

    /** Writes the uncompressed bytes to the outStream.
     * @param outStream : Stream to write uncompressed bytes into.
     * @throws IOException
     */
    public void writeUncompressedBytes(DataOutputStream outStream)
      throws IOException;

    /** Write compressed bytes to outStream. 
     * Note: that it will NOT compress the bytes if they are not compressed.
     * @param outStream : Stream to write compressed bytes into.
     */
    public void writeCompressedBytes(DataOutputStream outStream) 
      throws IllegalArgumentException, IOException;
  }
  
  private static class UncompressedBytes implements ValueBytes {
    private int dataSize;
    private byte[] data;
    
    private UncompressedBytes() {
      data = null;
      dataSize = 0;
    }
    
    private void reset(DataInputStream in, int length) throws IOException {
      data = new byte[length];
      dataSize = -1;
      
      in.readFully(data);
      dataSize = data.length;
    }
    
    public int getSize() {
      return dataSize;
    }
    
    public void writeUncompressedBytes(DataOutputStream outStream)
      throws IOException {
      outStream.write(data, 0, dataSize);
    }

    public void writeCompressedBytes(DataOutputStream outStream) 
      throws IllegalArgumentException, IOException {
      throw 
        new IllegalArgumentException("UncompressedBytes cannot be compressed!");
    }

  } // UncompressedBytes
  
  private static class CompressedBytes implements ValueBytes {
    private int dataSize;
    private byte[] data;
    DataInputBuffer rawData = null;
    CompressionCodec codec = null;
    CompressionInputStream decompressedStream = null;

    private CompressedBytes(CompressionCodec codec) {
      data = null;
      dataSize = 0;
      this.codec = codec;
    }

    private void reset(DataInputStream in, int length) throws IOException {
      data = new byte[length];
      dataSize = -1;

      in.readFully(data);
      dataSize = data.length;
    }
    
    public int getSize() {
      return dataSize;
    }
    
    public void writeUncompressedBytes(DataOutputStream outStream)
      throws IOException {
      if (decompressedStream == null) {
        rawData = new DataInputBuffer();
        decompressedStream = codec.createInputStream(rawData);
      } else {
        decompressedStream.resetState();
      }
      rawData.reset(data, 0, dataSize);

      byte[] buffer = new byte[8192];
      int bytesRead = 0;
      while ((bytesRead = decompressedStream.read(buffer, 0, 8192)) != -1) {
        outStream.write(buffer, 0, bytesRead);
      }
    }

    public void writeCompressedBytes(DataOutputStream outStream) 
      throws IllegalArgumentException, IOException {
      outStream.write(data, 0, dataSize);
    }

  } // CompressedBytes
  
  /**
   * The class encapsulating with the metadata of a file.
   * The metadata of a file is a list of attribute name/value
   * pairs of Text type.
   *
   */
  public static class Metadata implements Writable {

    private TreeMap<Text, Text> theMetadata;
    
    public Metadata() {
      this(new TreeMap<Text, Text>());
    }
    
    public Metadata(TreeMap<Text, Text> arg) {
      if (arg == null) {
        this.theMetadata = new TreeMap<Text, Text>();
      } else {
        this.theMetadata = arg;
      }
    }
    
    public Text get(Text name) {
      return this.theMetadata.get(name);
    }
    
    public void set(Text name, Text value) {
      this.theMetadata.put(name, value);
    }
    
    public TreeMap<Text, Text> getMetadata() {
      return new TreeMap<Text, Text>(this.theMetadata);
    }
    
    public void write(DataOutput out) throws IOException {
      out.writeInt(this.theMetadata.size());
      Iterator<Map.Entry<Text, Text>> iter =
        this.theMetadata.entrySet().iterator();
      while (iter.hasNext()) {
        Map.Entry<Text, Text> en = iter.next();
        en.getKey().write(out);
        en.getValue().write(out);
      }
    }

    public void readFields(DataInput in) throws IOException {
      int sz = in.readInt();
      if (sz < 0) throw new IOException("Invalid size: " + sz + " for file metadata object");
      this.theMetadata = new TreeMap<Text, Text>();
      for (int i = 0; i < sz; i++) {
        Text key = new Text();
        Text val = new Text();
        key.readFields(in);
        val.readFields(in);
        this.theMetadata.put(key, val);
      }    
    }
    
    public boolean equals(Metadata other) {
      if (other == null) return false;
      if (this.theMetadata.size() != other.theMetadata.size()) {
        return false;
      }
      Iterator<Map.Entry<Text, Text>> iter1 =
        this.theMetadata.entrySet().iterator();
      Iterator<Map.Entry<Text, Text>> iter2 =
        other.theMetadata.entrySet().iterator();
      while (iter1.hasNext() && iter2.hasNext()) {
        Map.Entry<Text, Text> en1 = iter1.next();
        Map.Entry<Text, Text> en2 = iter2.next();
        if (!en1.getKey().equals(en2.getKey())) {
          return false;
        }
        if (!en1.getValue().equals(en2.getValue())) {
          return false;
        }
      }
      if (iter1.hasNext() || iter2.hasNext()) {
        return false;
      }
      return true;
    }

    public int hashCode() {
      assert false : "hashCode not designed";
      return 42; // any arbitrary constant will do 
    }
    
    public String toString() {
      StringBuffer sb = new StringBuffer();
      sb.append("size: ").append(this.theMetadata.size()).append("\n");
      Iterator<Map.Entry<Text, Text>> iter =
        this.theMetadata.entrySet().iterator();
      while (iter.hasNext()) {
        Map.Entry<Text, Text> en = iter.next();
        sb.append("\t").append(en.getKey().toString()).append("\t").append(en.getValue().toString());
        sb.append("\n");
      }
      return sb.toString();
    }
  }
  
  /** Write key/value pairs to a sequence-format file. */
  public static class Writer {
    Configuration conf;
    FSDataOutputStream out;
    DataOutputBuffer buffer = new DataOutputBuffer();

    Class keyClass;
    Class valClass;

    private boolean compress;
    CompressionCodec codec = null;
    CompressionOutputStream deflateFilter = null;
    DataOutputStream deflateOut = null;
    Metadata metadata = null;

    // Insert a globally unique 16-byte value every few entries, so that one
    // can seek into the middle of a file and then synchronize with record
    // starts and ends by scanning for this value.
    long lastSyncPos;                     // position of last sync
    byte[] sync;                          // 16 random bytes
    {
      try {                                       // use hash of uid + host
        MessageDigest digester = MessageDigest.getInstance("MD5");
        digester.update((new UID()+"@"+InetAddress.getLocalHost()).getBytes());
        sync = digester.digest();
      } catch (Exception e) {
        throw new RuntimeException(e);
      }
    }

    /** Implicit constructor: needed for the period of transition!*/
    Writer()
    {}
    
    /** Create the named file. */
    public Writer(FileSystem fs, Configuration conf, Path name, 
                  Class keyClass, Class valClass)
      throws IOException {
      this(fs, conf, name, keyClass, valClass, null, new Metadata());
    }
    
    /** Create the named file with write-progress reporter. */
    public Writer(FileSystem fs, Configuration conf, Path name, 
                  Class keyClass, Class valClass, Progressable progress, Metadata metadata)
      throws IOException {
      init(name, conf, fs.create(name, progress), keyClass, valClass, false, null, metadata);
      initializeFileHeader();
      writeFileHeader();
      finalizeFileHeader();
    }
    
    /** Write to an arbitrary stream using a specified buffer size. */
    private Writer(Configuration conf, FSDataOutputStream out, 
                   Class keyClass, Class valClass, Metadata metadata)
      throws IOException {
      init(null, conf, out, keyClass, valClass, false, null, metadata);
      
      initializeFileHeader();
      writeFileHeader();
      finalizeFileHeader();
    }

    /** Write the initial part of file header. */
    void initializeFileHeader() 
      throws IOException{
      out.write(VERSION);
    }

    /** Write the final part of file header. */
    void finalizeFileHeader() 
      throws IOException{
      out.write(sync);                       // write the sync bytes
      out.flush();                           // flush header
    }
    
    boolean isCompressed() { return compress; }
    boolean isBlockCompressed() { return false; }
    
    /** Write and flush the file header. */
    void writeFileHeader() 
      throws IOException {
      Text.writeString(out, keyClass.getName());
      Text.writeString(out, valClass.getName());
      
      out.writeBoolean(this.isCompressed());
      out.writeBoolean(this.isBlockCompressed());
      
      if (this.isCompressed()) {
        Text.writeString(out, (codec.getClass()).getName());
      }
      this.metadata.write(out);
    }
    
    /** Initialize. */
    void init(Path name, Configuration conf, FSDataOutputStream out,
              Class keyClass, Class valClass,
              boolean compress, CompressionCodec codec, Metadata metadata) 
      throws IOException {
      this.conf = conf;
      this.out = out;
      this.keyClass = keyClass;
      this.valClass = valClass;
      this.compress = compress;
      this.codec = codec;
      this.metadata = metadata;
      if (this.codec != null) {
        ReflectionUtils.setConf(this.codec, this.conf);
        this.deflateFilter = this.codec.createOutputStream(buffer);
        this.deflateOut = 
          new DataOutputStream(new BufferedOutputStream(deflateFilter));
      }
    }
    
    /** Returns the class of keys in this file. */
    public Class getKeyClass() { return keyClass; }

    /** Returns the class of values in this file. */
    public Class getValueClass() { return valClass; }

    /** Returns the compression codec of data in this file. */
    public CompressionCodec getCompressionCodec() { return codec; }
    
    /** create a sync point */
    public void sync() throws IOException {
    }

    /** Returns the configuration of this file. */
    Configuration getConf() { return conf; }
    
    /** Close the file. */
    public synchronized void close() throws IOException {
      if (out != null) {
        out.close();
        out = null;
      }
    }

    synchronized void checkAndWriteSync() throws IOException {
      if (sync != null &&
          out.getPos() >= lastSyncPos+SYNC_INTERVAL) { // time to emit sync
        lastSyncPos = out.getPos();               // update lastSyncPos
        //LOG.info("sync@"+lastSyncPos);
        out.writeInt(SYNC_ESCAPE);                // escape it
        out.write(sync);                          // write sync
      }
    }

    /** Append a key/value pair. */
    public synchronized void append(Writable key, Writable val)
      throws IOException {
      if (key.getClass() != keyClass)
        throw new IOException("wrong key class: "+key.getClass().getName()
                              +" is not "+keyClass);
      if (val.getClass() != valClass)
        throw new IOException("wrong value class: "+val.getClass().getName()
                              +" is not "+valClass);

      buffer.reset();

      // Append the 'key'
      key.write(buffer);
      int keyLength = buffer.getLength();
      if (keyLength == 0)
        throw new IOException("zero length keys not allowed: " + key);

      // Append the 'value'
      if (compress) {
        deflateFilter.resetState();
        val.write(deflateOut);
        deflateOut.flush();
        deflateFilter.finish();
      } else {
        val.write(buffer);
      }

      // Write the record out
      checkAndWriteSync();                                // sync
      out.writeInt(buffer.getLength());                   // total record length
      out.writeInt(keyLength);                            // key portion length
      out.write(buffer.getData(), 0, buffer.getLength()); // data
    }

    public synchronized void appendRaw(
                                       byte[] keyData, int keyOffset, int keyLength, ValueBytes val) 
      throws IOException {
      if (keyLength == 0)
        throw new IOException("zero length keys not allowed: " + keyLength);

      UncompressedBytes value = (UncompressedBytes)val;
      int valLength = value.getSize();

      checkAndWriteSync();
      
      out.writeInt(keyLength+valLength);          // total record length
      out.writeInt(keyLength);                    // key portion length
      out.write(keyData, keyOffset, keyLength);   // key
      val.writeUncompressedBytes(out);            // value
    }

    /** Returns the current length of the output file.
     *
     * <p>This always returns a synchronized position.  In other words,
     * immediately after calling {@link SequenceFile.Reader#seek(long)} with a position
     * returned by this method, {@link SequenceFile.Reader#next(Writable)} may be called.  However
     * the key may be earlier in the file than key last written when this
     * method was called (e.g., with block-compression, it may be the first key
     * in the block that was being written when this method was called).
     */
    public synchronized long getLength() throws IOException {
      return out.getPos();
    }

  } // class Writer

  /** Write key/compressed-value pairs to a sequence-format file. */
  static class RecordCompressWriter extends Writer {
    
    /** Create the named file. */
    public RecordCompressWriter(FileSystem fs, Configuration conf, Path name, 
                                Class keyClass, Class valClass, CompressionCodec codec) 
      throws IOException {
      super.init(name, conf, fs.create(name), keyClass, valClass, true, codec, new Metadata());
      
      initializeFileHeader();
      writeFileHeader();
      finalizeFileHeader();
    }
    
    /** Create the named file with write-progress reporter. */
    public RecordCompressWriter(FileSystem fs, Configuration conf, Path name, 
                                Class keyClass, Class valClass, CompressionCodec codec,
                                Progressable progress, Metadata metadata)
      throws IOException {
      super.init(name, conf, fs.create(name, progress), 
                 keyClass, valClass, true, codec, metadata);
      
      initializeFileHeader();
      writeFileHeader();
      finalizeFileHeader();
    }
    
    /** Create the named file with write-progress reporter. */
    public RecordCompressWriter(FileSystem fs, Configuration conf, Path name, 
                                Class keyClass, Class valClass, CompressionCodec codec,
                                Progressable progress)
      throws IOException {
      this(fs, conf, name, keyClass, valClass, codec, progress, new Metadata());
    }
    
    /** Write to an arbitrary stream using a specified buffer size. */
    private RecordCompressWriter(Configuration conf, FSDataOutputStream out,
                                 Class keyClass, Class valClass, CompressionCodec codec, Metadata metadata)
      throws IOException {
      super.init(null, conf, out, keyClass, valClass, true, codec, metadata);
      
      initializeFileHeader();
      writeFileHeader();
      finalizeFileHeader();
      
    }
    
    boolean isCompressed() { return true; }
    boolean isBlockCompressed() { return false; }

    /** Append a key/value pair. */
    public synchronized void append(Writable key, Writable val)
      throws IOException {
      if (key.getClass() != keyClass)
        throw new IOException("wrong key class: "+key.getClass().getName()
                              +" is not "+keyClass);
      if (val.getClass() != valClass)
        throw new IOException("wrong value class: "+val.getClass().getName()
                              +" is not "+valClass);

      buffer.reset();

      // Append the 'key'
      key.write(buffer);
      int keyLength = buffer.getLength();
      if (keyLength == 0)
        throw new IOException("zero length keys not allowed: " + key);

      // Compress 'value' and append it
      deflateFilter.resetState();
      val.write(deflateOut);
      deflateOut.flush();
      deflateFilter.finish();

      // Write the record out
      checkAndWriteSync();                                // sync
      out.writeInt(buffer.getLength());                   // total record length
      out.writeInt(keyLength);                            // key portion length
      out.write(buffer.getData(), 0, buffer.getLength()); // data
    }

    /** Append a key/value pair. */
    public synchronized void appendRaw(
                                       byte[] keyData, int keyOffset, int keyLength,
                                       ValueBytes val
                                       ) throws IOException {

      if (keyLength == 0)
        throw new IOException("zero length keys not allowed");

      CompressedBytes value = (CompressedBytes)val;
      int valLength = value.getSize();
      
      checkAndWriteSync();                        // sync
      out.writeInt(keyLength+valLength);          // total record length
      out.writeInt(keyLength);                    // key portion length
      out.write(keyData, keyOffset, keyLength);   // 'key' data
      val.writeCompressedBytes(out);              // 'value' data
    }
    

    public void sync() throws IOException {
    }
   
  } // RecordCompressionWriter

  /** Write compressed key/value blocks to a sequence-format file. */
  static class BlockCompressWriter extends Writer {
    
    private int noBufferedRecords = 0;
    
    private DataOutputBuffer keyLenBuffer = new DataOutputBuffer();
    private DataOutputBuffer keyBuffer = new DataOutputBuffer();

    private DataOutputBuffer valLenBuffer = new DataOutputBuffer();
    private DataOutputBuffer valBuffer = new DataOutputBuffer();

    private int compressionBlockSize;
    
    /** Create the named file. */
    public BlockCompressWriter(FileSystem fs, Configuration conf, Path name, 
                               Class keyClass, Class valClass, CompressionCodec codec) 
      throws IOException {
      super.init(name, conf, fs.create(name), keyClass, valClass, true, codec, new Metadata());
      init(conf.getInt("io.seqfile.compress.blocksize", 1000000));
      
      initializeFileHeader();
      writeFileHeader();
      finalizeFileHeader();
    }
    
    /** Create the named file with write-progress reporter. */
    public BlockCompressWriter(FileSystem fs, Configuration conf, Path name, 
                               Class keyClass, Class valClass, CompressionCodec codec,
                               Progressable progress, Metadata metadata)
      throws IOException {
      super.init(name, conf, fs.create(name, progress), keyClass, valClass, 
                 true, codec, metadata);
      init(conf.getInt("io.seqfile.compress.blocksize", 1000000));
      
      initializeFileHeader();
      writeFileHeader();
      finalizeFileHeader();
    }
    
    /** Create the named file with write-progress reporter. */
    public BlockCompressWriter(FileSystem fs, Configuration conf, Path name, 
                               Class keyClass, Class valClass, CompressionCodec codec,
                               Progressable progress)
      throws IOException {
      this(fs, conf, name, keyClass, valClass, codec, progress, new Metadata());
    }
    
    /** Write to an arbitrary stream using a specified buffer size. */
    private BlockCompressWriter(Configuration conf, FSDataOutputStream out,
                                Class keyClass, Class valClass, CompressionCodec codec, Metadata metadata)
      throws IOException {
      super.init(null, conf, out, keyClass, valClass, true, codec, metadata);
      init(1000000);
      
      initializeFileHeader();
      writeFileHeader();
      finalizeFileHeader();
    }
    
    boolean isCompressed() { return true; }
    boolean isBlockCompressed() { return true; }

    /** Initialize */
    void init(int compressionBlockSize) {
      this.compressionBlockSize = compressionBlockSize;
    }
    
    /** Workhorse to check and write out compressed data/lengths */
    private synchronized 
      void writeBuffer(DataOutputBuffer uncompressedDataBuffer) 
      throws IOException {
      deflateFilter.resetState();
      buffer.reset();
      deflateOut.write(uncompressedDataBuffer.getData(), 0, 
                       uncompressedDataBuffer.getLength());
      deflateOut.flush();
      deflateFilter.finish();
      
      WritableUtils.writeVInt(out, buffer.getLength());
      out.write(buffer.getData(), 0, buffer.getLength());
    }
    
    /** Compress and flush contents to dfs */
    private synchronized void writeBlock() throws IOException {
      if (noBufferedRecords > 0) {
        // Write 'sync' marker
        if (sync != null) {
          out.writeInt(SYNC_ESCAPE);
          out.write(sync);
        }
        
        // No. of records
        WritableUtils.writeVInt(out, noBufferedRecords);
        
        // Write 'keys' and lengths
        writeBuffer(keyLenBuffer);
        writeBuffer(keyBuffer);
        
        // Write 'values' and lengths
        writeBuffer(valLenBuffer);
        writeBuffer(valBuffer);
        
        // Flush the file-stream
        out.flush();
        
        // Reset internal states
        keyLenBuffer.reset();
        keyBuffer.reset();
        valLenBuffer.reset();
        valBuffer.reset();
        noBufferedRecords = 0;
      }
      
    }
    
    /** Close the file. */
    public synchronized void close() throws IOException {
      if (out != null) {
        writeBlock();
        out.close();
        out = null;
      }
    }

    public void sync() throws IOException {
      writeBlock();
    }

    /** Append a key/value pair. */
    public synchronized void append(Writable key, Writable val)
      throws IOException {
      if (key.getClass() != keyClass)
        throw new IOException("wrong key class: "+key+" is not "+keyClass);
      if (val.getClass() != valClass)
        throw new IOException("wrong value class: "+val+" is not "+valClass);

      // Save key/value into respective buffers 
      int oldKeyLength = keyBuffer.getLength();
      key.write(keyBuffer);
      int keyLength = keyBuffer.getLength() - oldKeyLength;
      if (keyLength == 0)
        throw new IOException("zero length keys not allowed: " + key);
      WritableUtils.writeVInt(keyLenBuffer, keyLength);

      int oldValLength = valBuffer.getLength();
      val.write(valBuffer);
      int valLength = valBuffer.getLength() - oldValLength;
      WritableUtils.writeVInt(valLenBuffer, valLength);
      
      // Added another key/value pair
      ++noBufferedRecords;
      
      // Compress and flush?
      int currentBlockSize = keyBuffer.getLength() + valBuffer.getLength();
      if (currentBlockSize >= compressionBlockSize) {
        writeBlock();
      }
    }
    
    /** Append a key/value pair. */
    public synchronized void appendRaw(
                                       byte[] keyData, int keyOffset, int keyLength,
                                       ValueBytes val
                                       ) throws IOException {
      
      if (keyLength == 0)
        throw new IOException("zero length keys not allowed");

      UncompressedBytes value = (UncompressedBytes)val;
      int valLength = value.getSize();
      
      // Save key/value data in relevant buffers
      WritableUtils.writeVInt(keyLenBuffer, keyLength);
      keyBuffer.write(keyData, keyOffset, keyLength);
      WritableUtils.writeVInt(valLenBuffer, valLength);
      val.writeUncompressedBytes(valBuffer);

      // Added another key/value pair
      ++noBufferedRecords;

      // Compress and flush?
      int currentBlockSize = keyBuffer.getLength() + valBuffer.getLength(); 
      if (currentBlockSize >= compressionBlockSize) {
        writeBlock();
      }
    }
  
  } // BlockCompressionWriter
  
  /** Reads key/value pairs from a sequence-format file. */
  public static class Reader {
    private Path file;
    private FSDataInputStream in;
    private DataOutputBuffer outBuf = new DataOutputBuffer();

    private byte version;

    private Class keyClass;
    private Class valClass;

    private CompressionCodec codec = null;
    private Metadata metadata = null;
    
    private byte[] sync = new byte[SYNC_HASH_SIZE];
    private byte[] syncCheck = new byte[SYNC_HASH_SIZE];
    private boolean syncSeen;

    private long end;
    private int keyLength;
    private int recordLength;

    private boolean decompress;
    private boolean blockCompressed;
    
    private Configuration conf;

    private int noBufferedRecords = 0;
    private boolean lazyDecompress = true;
    private boolean valuesDecompressed = true;
    
    private int noBufferedKeys = 0;
    private int noBufferedValues = 0;
    
    private DataInputBuffer keyLenBuffer = null;
    private CompressionInputStream keyLenInFilter = null;
    private DataInputStream keyLenIn = null;
    private DataInputBuffer keyBuffer = null;
    private CompressionInputStream keyInFilter = null;
    private DataInputStream keyIn = null;

    private DataInputBuffer valLenBuffer = null;
    private CompressionInputStream valLenInFilter = null;
    private DataInputStream valLenIn = null;
    private DataInputBuffer valBuffer = null;
    private CompressionInputStream valInFilter = null;
    private DataInputStream valIn = null;

    /** Open the named file. */
    public Reader(FileSystem fs, Path file, Configuration conf)
      throws IOException {
      this(fs, file, conf.getInt("io.file.buffer.size", 4096), conf);
    }

    private Reader(FileSystem fs, Path name, int bufferSize,
                   Configuration conf) throws IOException {
      this.file = name;
      this.in = fs.open(file, bufferSize);
      this.end = fs.getLength(file);
      this.conf = conf;
      init();
    }
    
    private Reader(FileSystem fs, Path file, int bufferSize, long start,
                   long length, Configuration conf) throws IOException {
      this.file = file;
      this.in = fs.open(file, bufferSize);
      this.conf = conf;
      seek(start);
      this.end = in.getPos() + length;
      init();
    }
    
    private void init() throws IOException {
      byte[] versionBlock = new byte[VERSION.length];
      in.readFully(versionBlock);

      if ((versionBlock[0] != VERSION[0]) ||
          (versionBlock[1] != VERSION[1]) ||
          (versionBlock[2] != VERSION[2]))
        throw new IOException(file + " not a SequenceFile");

      // Set 'version'
      version = versionBlock[3];
      if (version > VERSION[3])
        throw new VersionMismatchException(VERSION[3], version);

      if (version < BLOCK_COMPRESS_VERSION) {
        UTF8 className = new UTF8();
        
        className.readFields(in);                   // read key class name
        this.keyClass = WritableName.getClass(className.toString(), conf);
        
        className.readFields(in);                   // read val class name
        this.valClass = WritableName.getClass(className.toString(), conf);
      } else {
        this.keyClass = WritableName.getClass(Text.readString(in), conf);
        this.valClass = WritableName.getClass(Text.readString(in), conf);
      }

      if (version > 2) {                          // if version > 2
        this.decompress = in.readBoolean();       // is compressed?
      } else {
        decompress = false;
      }

      if (version >= BLOCK_COMPRESS_VERSION) {    // if version >= 4
        this.blockCompressed = in.readBoolean();  // is block-compressed?
      } else {
        blockCompressed = false;
      }
      
      // if version >= 5
      // setup the compression codec
      if (decompress) {
        if (version >= CUSTOM_COMPRESS_VERSION) {
          String codecClassname = Text.readString(in);
          try {
            Class codecClass = conf.getClassByName(codecClassname);
            this.codec = (CompressionCodec)
              ReflectionUtils.newInstance(codecClass, conf);
          } catch (ClassNotFoundException cnfe) {
            throw new IllegalArgumentException("Unknown codec: " + 
                                               codecClassname, cnfe);
          }
        } else {
          codec = new DefaultCodec();
          ((Configurable)codec).setConf(conf);
        }
      }
      
      this.metadata = new Metadata();
      if (version >= VERSION_WITH_METADATA) {    // if version >= 6
        this.metadata.readFields(in);
      }
      
      if (version > 1) {                          // if version > 1
        in.readFully(sync);                       // read sync bytes
      }
      
      // Initialize
      valBuffer = new DataInputBuffer();
      if (decompress) {
        valInFilter = this.codec.createInputStream(valBuffer);
        valIn = new DataInputStream(valInFilter);
      } else {
        valIn = valBuffer;
      }
      
      if (blockCompressed) {
        keyLenBuffer = new DataInputBuffer();
        keyBuffer = new DataInputBuffer();
        valLenBuffer = new DataInputBuffer();
        
        keyLenInFilter = this.codec.createInputStream(keyLenBuffer);
        keyLenIn = new DataInputStream(keyLenInFilter);

        keyInFilter = this.codec.createInputStream(keyBuffer);
        keyIn = new DataInputStream(keyInFilter);

        valLenInFilter = this.codec.createInputStream(valLenBuffer);
        valLenIn = new DataInputStream(valLenInFilter);
      }
    }
    
    /** Close the file. */
    public synchronized void close() throws IOException {
      in.close();
    }

    /** Returns the class of keys in this file. */
    public Class getKeyClass() { return keyClass; }

    /** Returns the class of values in this file. */
    public Class getValueClass() { return valClass; }

    /** Returns true if values are compressed. */
    public boolean isCompressed() { return decompress; }
    
    /** Returns true if records are block-compressed. */
    public boolean isBlockCompressed() { return blockCompressed; }
    
    /** Returns the compression codec of data in this file. */
    public CompressionCodec getCompressionCodec() { return codec; }

    /** Returns the metadata object of the file */
    public Metadata getMetadata() {
      return this.metadata;
    }
    
    /** Returns the configuration used for this file. */
    Configuration getConf() { return conf; }
    
    /** Read a compressed buffer */
    private synchronized void readBuffer(DataInputBuffer buffer, 
                                         CompressionInputStream filter) throws IOException {
      // Read data into a temporary buffer
      DataOutputBuffer dataBuffer = new DataOutputBuffer();

      try {
        int dataBufferLength = WritableUtils.readVInt(in);
        dataBuffer.write(in, dataBufferLength);
      
        // Set up 'buffer' connected to the input-stream
        buffer.reset(dataBuffer.getData(), 0, dataBuffer.getLength());
      } finally {
        dataBuffer.close();
      }

      // Reset the codec
      filter.resetState();
    }
    
    /** Read the next 'compressed' block */
    private synchronized void readBlock() throws IOException {
      // Check if we need to throw away a whole block of 
      // 'values' due to 'lazy decompression' 
      if (lazyDecompress && !valuesDecompressed) {
        in.seek(WritableUtils.readVInt(in)+in.getPos());
        in.seek(WritableUtils.readVInt(in)+in.getPos());
      }
      
      // Reset internal states
      noBufferedKeys = 0; noBufferedValues = 0; noBufferedRecords = 0;
      valuesDecompressed = false;

      //Process sync
      if (sync != null) {
        in.readInt();
        in.readFully(syncCheck);                // read syncCheck
        if (!Arrays.equals(sync, syncCheck))    // check it
          throw new IOException("File is corrupt!");
      }
      syncSeen = true;

      // Read number of records in this block
      noBufferedRecords = WritableUtils.readVInt(in);
      
      // Read key lengths and keys
      readBuffer(keyLenBuffer, keyLenInFilter);
      readBuffer(keyBuffer, keyInFilter);
      noBufferedKeys = noBufferedRecords;
      
      // Read value lengths and values
      if (!lazyDecompress) {
        readBuffer(valLenBuffer, valLenInFilter);
        readBuffer(valBuffer, valInFilter);
        noBufferedValues = noBufferedRecords;
        valuesDecompressed = true;
      }
    }

    /** 
     * Position valLenIn/valIn to the 'value' 
     * corresponding to the 'current' key 
     */
    private synchronized void seekToCurrentValue() throws IOException {
      if (!blockCompressed) {
        if (decompress) {
          valInFilter.resetState();
        }
        valBuffer.reset();
      } else {
        // Check if this is the first value in the 'block' to be read
        if (lazyDecompress && !valuesDecompressed) {
          // Read the value lengths and values
          readBuffer(valLenBuffer, valLenInFilter);
          readBuffer(valBuffer, valInFilter);
          noBufferedValues = noBufferedRecords;
          valuesDecompressed = true;
        }
        
        // Calculate the no. of bytes to skip
        // Note: 'current' key has already been read!
        int skipValBytes = 0;
        int currentKey = noBufferedKeys + 1;          
        for (int i=noBufferedValues; i > currentKey; --i) {
          skipValBytes += WritableUtils.readVInt(valLenIn);
          --noBufferedValues;
        }
        
        // Skip to the 'val' corresponding to 'current' key
        if (skipValBytes > 0) {
          if (valIn.skipBytes(skipValBytes) != skipValBytes) {
            throw new IOException("Failed to seek to " + currentKey + 
                                  "(th) value!");
          }
        }
      }
    }

    /**
     * Get the 'value' corresponding to the last read 'key'.
     * @param val : The 'value' to be read.
     * @throws IOException
     */
    public synchronized void getCurrentValue(Writable val) 
      throws IOException {
      if (val instanceof Configurable) {
        ((Configurable) val).setConf(this.conf);
      }

      // Position stream to 'current' value
      seekToCurrentValue();

      if (!blockCompressed) {
        val.readFields(valIn);
        
        if (valIn.read() > 0) {
          LOG.info("available bytes: " + valIn.available());
          throw new IOException(val+" read "+(valBuffer.getPosition()-keyLength)
                                + " bytes, should read " +
                                (valBuffer.getLength()-keyLength));
        }
      } else {
        // Get the value
        int valLength = WritableUtils.readVInt(valLenIn);
        val.readFields(valIn);
        
        // Read another compressed 'value'
        --noBufferedValues;
        
        // Sanity check
        if (valLength < 0) {
          LOG.debug(val + " is a zero-length value");
        }
      }

    }
    
    /** Read the next key in the file into <code>key</code>, skipping its
     * value.  True if another entry exists, and false at end of file. */
    public synchronized boolean next(Writable key) throws IOException {
      if (key.getClass() != keyClass)
        throw new IOException("wrong key class: "+key.getClass().getName()
                              +" is not "+keyClass);

      if (!blockCompressed) {
        outBuf.reset();
        
        keyLength = next(outBuf);
        if (keyLength < 0)
          return false;
        
        valBuffer.reset(outBuf.getData(), outBuf.getLength());
        
        key.readFields(valBuffer);
        valBuffer.mark(0);
        if (valBuffer.getPosition() != keyLength)
          throw new IOException(key + " read " + valBuffer.getPosition()
                                + " bytes, should read " + keyLength);
      } else {
        //Reset syncSeen
        syncSeen = false;
        
        if (noBufferedKeys == 0) {
          try {
            readBlock();
          } catch (EOFException eof) {
            return false;
          }
        }
        
        int keyLength = WritableUtils.readVInt(keyLenIn);
        
        // Sanity check
        if (keyLength < 0) {
          return false;
        }
        
        //Read another compressed 'key'
        key.readFields(keyIn);
        --noBufferedKeys;
      }

      return true;
    }

    /** Read the next key/value pair in the file into <code>key</code> and
     * <code>val</code>.  Returns true if such a pair exists and false when at
     * end of file */
    public synchronized boolean next(Writable key, Writable val)
      throws IOException {
      if (val.getClass() != valClass)
        throw new IOException("wrong value class: "+val+" is not "+valClass);

      boolean more = next(key);
      
      if (more) {
        getCurrentValue(val);
      }

      return more;
    }
    
    private synchronized int checkAndReadSync(int length) 
      throws IOException {
      if (version > 1 && sync != null &&
          length == SYNC_ESCAPE) {              // process a sync entry
        //LOG.info("sync@"+in.getPos());
        in.readFully(syncCheck);                // read syncCheck
        if (!Arrays.equals(sync, syncCheck))    // check it
          throw new IOException("File is corrupt!");
        syncSeen = true;
        length = in.readInt();                  // re-read length
      } else {
        syncSeen = false;
      }
      
      return length;
    }
    
    /** Read the next key/value pair in the file into <code>buffer</code>.
     * Returns the length of the key read, or -1 if at end of file.  The length
     * of the value may be computed by calling buffer.getLength() before and
     * after calls to this method. */
    /** @deprecated Call {@link #nextRaw(DataOutputBuffer,SequenceFile.ValueBytes)}. */
    public synchronized int next(DataOutputBuffer buffer) throws IOException {
      // Unsupported for block-compressed sequence files
      if (blockCompressed) {
        throw new IOException("Unsupported call for block-compressed" +
                              " SequenceFiles - use SequenceFile.Reader.next(DataOutputStream, ValueBytes)");
      }
      if (in.getPos() >= end)
        return -1;

      try {
        int length = checkAndReadSync(in.readInt());
        int keyLength = in.readInt();
        buffer.write(in, length);
        return keyLength;
      } catch (ChecksumException e) {             // checksum failure
        handleChecksumException(e);
        return next(buffer);
      }
    }

    public ValueBytes createValueBytes() {
      ValueBytes val = null;
      if (!decompress || blockCompressed) {
        val = new UncompressedBytes();
      } else {
        val = new CompressedBytes(codec);
      }
      return val;
    }

    /**
     * Read 'raw' records.
     * @param key - The buffer into which the key is read
     * @param val - The 'raw' value
     * @return Returns the total record length
     * @throws IOException
     */
    public synchronized int nextRaw(DataOutputBuffer key, ValueBytes val) 
      throws IOException {
      if (!blockCompressed) {
        if (in.getPos() >= end) 
          return -1;

        int length = checkAndReadSync(in.readInt());
        int keyLength = in.readInt();
        int valLength = length - keyLength;
        key.write(in, keyLength);
        if (decompress) {
          CompressedBytes value = (CompressedBytes)val;
          value.reset(in, valLength);
        } else {
          UncompressedBytes value = (UncompressedBytes)val;
          value.reset(in, valLength);
        }
        
        return length;
      } else {
        //Reset syncSeen
        syncSeen = false;
        
        // Read 'key'
        if (noBufferedKeys == 0) {
          if (in.getPos() >= end) 
            return -1;

          try { 
            readBlock();
          } catch (EOFException eof) {
            return -1;
          }
        }
        int keyLength = WritableUtils.readVInt(keyLenIn);
        if (keyLength < 0) {
          throw new IOException("zero length key found!");
        }
        key.write(keyIn, keyLength);
        --noBufferedKeys;
        
        // Read raw 'value'
        seekToCurrentValue();
        int valLength = WritableUtils.readVInt(valLenIn);
        UncompressedBytes rawValue = (UncompressedBytes)val;
        rawValue.reset(valIn, valLength);
        --noBufferedValues;
        
        return (keyLength+valLength);
      }
      
    }

    /**
     * Read 'raw' keys.
     * @param key - The buffer into which the key is read
     * @return Returns the key length
     * @throws IOException
     */
    public int nextRawKey(DataOutputBuffer key) 
      throws IOException {
      if (!blockCompressed) {
        if (in.getPos() >= end) 
          return -1;

        recordLength = checkAndReadSync(in.readInt());
        keyLength = in.readInt();
        key.write(in, keyLength);
        return keyLength;
      } else {
        //Reset syncSeen
        syncSeen = false;
        
        // Read 'key'
        if (noBufferedKeys == 0) {
          if (in.getPos() >= end) 
            return -1;

          try { 
            readBlock();
          } catch (EOFException eof) {
            return -1;
          }
        }
        int keyLength = WritableUtils.readVInt(keyLenIn);
        if (keyLength < 0) {
          throw new IOException("zero length key found!");
        }
        key.write(keyIn, keyLength);
        --noBufferedKeys;
        
        return keyLength;
      }
      
    }

    /**
     * Read 'raw' values.
     * @param val - The 'raw' value
     * @return Returns the value length
     * @throws IOException
     */
    public synchronized int nextRawValue(ValueBytes val) 
      throws IOException {
      
      // Position stream to current value
      seekToCurrentValue();
 
      if (!blockCompressed) {
        int valLength = recordLength - keyLength;
        if (decompress) {
          CompressedBytes value = (CompressedBytes)val;
          value.reset(in, valLength);
        } else {
          UncompressedBytes value = (UncompressedBytes)val;
          value.reset(in, valLength);
        }
         
        return valLength;
      } else {
        int valLength = WritableUtils.readVInt(valLenIn);
        UncompressedBytes rawValue = (UncompressedBytes)val;
        rawValue.reset(valIn, valLength);
        --noBufferedValues;
        return valLength;
      }
      
    }

    private void handleChecksumException(ChecksumException e)
      throws IOException {
      if (this.conf.getBoolean("io.skip.checksum.errors", false)) {
        LOG.warn("Bad checksum at "+getPosition()+". Skipping entries.");
        sync(getPosition()+this.conf.getInt("io.bytes.per.checksum", 512));
      } else {
        throw e;
      }
    }

    /** Set the current byte position in the input file.
     *
     * <p>The position passed must be a position returned by {@link
     * SequenceFile.Writer#getLength()} when writing this file.  To seek to an arbitrary
     * position, use {@link SequenceFile.Reader#sync(long)}.
     */
    public synchronized void seek(long position) throws IOException {
      in.seek(position);
      if (blockCompressed) {                      // trigger block read
        noBufferedKeys = 0;
        valuesDecompressed = true;
      }
    }

    /** Seek to the next sync mark past a given position.*/
    public synchronized void sync(long position) throws IOException {
      if (position+SYNC_SIZE >= end) {
        seek(end);
        return;
      }

      try {
        seek(position+4);                         // skip escape
        in.readFully(syncCheck);
        int syncLen = sync.length;
        for (int i = 0; in.getPos() < end; i++) {
          int j = 0;
          for (; j < syncLen; j++) {
            if (sync[j] != syncCheck[(i+j)%syncLen])
              break;
          }
          if (j == syncLen) {
            in.seek(in.getPos() - SYNC_SIZE);     // position before sync
            return;
          }
          syncCheck[i%syncLen] = in.readByte();
        }
      } catch (ChecksumException e) {             // checksum failure
        handleChecksumException(e);
      }
    }

    /** Returns true iff the previous call to next passed a sync mark.*/
    public boolean syncSeen() { return syncSeen; }

    /** Return the current byte position in the input file. */
    public synchronized long getPosition() throws IOException {
      return in.getPos();
    }

    /** Returns the name of the file. */
    public String toString() {
      return file.toString();
    }

  }

  /** Sorts key/value pairs in a sequence-format file.
   *
   * <p>For best performance, applications should make sure that the {@link
   * Writable#readFields(DataInput)} implementation of their keys is
   * very efficient.  In particular, it should avoid allocating memory.
   */
  public static class Sorter {

    private WritableComparator comparator;

    private MergeSort mergeSort; //the implementation of merge sort
    
    private Path[] inFiles;                     // when merging or sorting

    private Path outFile;

    private int memory; // bytes
    private int factor; // merged per pass

    private FileSystem fs = null;

    private Class keyClass;
    private Class valClass;

    private Configuration conf;

    /** Sort and merge files containing the named classes. */
    public Sorter(FileSystem fs, Class keyClass, Class valClass, Configuration conf)  {
      this(fs, new WritableComparator(keyClass), valClass, conf);
    }

    /** Sort and merge using an arbitrary {@link WritableComparator}. */
    public Sorter(FileSystem fs, WritableComparator comparator, Class valClass, 
                  Configuration conf) {
      this.fs = fs;
      this.comparator = comparator;
      this.keyClass = comparator.getKeyClass();
      this.valClass = valClass;
      this.memory = conf.getInt("io.sort.mb", 100) * 1024 * 1024;
      this.factor = conf.getInt("io.sort.factor", 100);
      this.conf = conf;
    }

    /** Set the number of streams to merge at once.*/
    public void setFactor(int factor) { this.factor = factor; }

    /** Get the number of streams to merge at once.*/
    public int getFactor() { return factor; }

    /** Set the total amount of buffer memory, in bytes.*/
    public void setMemory(int memory) { this.memory = memory; }

    /** Get the total amount of buffer memory, in bytes.*/
    public int getMemory() { return memory; }

    /** 
     * Perform a file sort from a set of input files into an output file.
     * @param inFiles the files to be sorted
     * @param outFile the sorted output file
     * @param deleteInput should the input files be deleted as they are read?
     */
    public void sort(Path[] inFiles, Path outFile,
                     boolean deleteInput) throws IOException {
      if (fs.exists(outFile)) {
        throw new IOException("already exists: " + outFile);
      }

      this.inFiles = inFiles;
      this.outFile = outFile;

      int segments = sortPass(deleteInput);
      if (segments > 1) {
        mergePass(outFile.getParent());
      }
    }

    /** 
     * Perform a file sort from a set of input files and return an iterator.
     * @param inFiles the files to be sorted
     * @param tempDir the directory where temp files are created during sort
     * @param deleteInput should the input files be deleted as they are read?
     * @return iterator the RawKeyValueIterator
     */
    public RawKeyValueIterator sortAndIterate(Path[] inFiles, Path tempDir, 
                                              boolean deleteInput) throws IOException {
      Path outFile = new Path(tempDir + Path.SEPARATOR + "all.2");
      if (fs.exists(outFile)) {
        throw new IOException("already exists: " + outFile);
      }
      this.inFiles = inFiles;
      //outFile will basically be used as prefix for temp files in the cases
      //where sort outputs multiple sorted segments. For the single segment
      //case, the outputFile itself will contain the sorted data for that
      //segment
      this.outFile = outFile;

      int segments = sortPass(deleteInput);
      if (segments > 1)
        return merge(outFile.suffix(".0"), outFile.suffix(".0.index"), 
                     tempDir);
      else if (segments == 1)
        return merge(new Path[]{outFile}, true, tempDir);
      else return null;
    }

    /**
     * The backwards compatible interface to sort.
     * @param inFile the input file to sort
     * @param outFile the sorted output file
     */
    public void sort(Path inFile, Path outFile) throws IOException {
      sort(new Path[]{inFile}, outFile, false);
    }
    
    private int sortPass(boolean deleteInput) throws IOException {
      LOG.debug("running sort pass");
      SortPass sortPass = new SortPass();         // make the SortPass
      mergeSort = new MergeSort(sortPass.new SeqFileComparator());
      try {
        return sortPass.run(deleteInput);         // run it
      } finally {
        sortPass.close();                         // close it
      }
    }

    private class SortPass {
      private int memoryLimit = memory/4;
      private int recordLimit = 1000000;
      
      private DataOutputBuffer rawKeys = new DataOutputBuffer();
      private byte[] rawBuffer;

      private int[] keyOffsets = new int[1024];
      private int[] pointers = new int[keyOffsets.length];
      private int[] pointersCopy = new int[keyOffsets.length];
      private int[] keyLengths = new int[keyOffsets.length];
      private ValueBytes[] rawValues = new ValueBytes[keyOffsets.length];
      
      private ArrayList segmentLengths = new ArrayList();
      
      private Reader in = null;
      private FSDataOutputStream out = null;
      private FSDataOutputStream indexOut = null;
      private Path outName;

      public int run(boolean deleteInput) throws IOException {
        int segments = 0;
        int currentFile = 0;
        boolean atEof = (currentFile >= inFiles.length);
        boolean isCompressed = false;
        boolean isBlockCompressed = false;
        CompressionCodec codec = null;
        segmentLengths.clear();
        if (atEof) {
          return 0;
        }
        
        // Initialize
        in = new Reader(fs, inFiles[currentFile], conf);
        isCompressed = in.isCompressed();
        isBlockCompressed = in.isBlockCompressed();
        codec = in.getCompressionCodec();
        
        for (int i=0; i < rawValues.length; ++i) {
          rawValues[i] = null;
        }
        
        while (!atEof) {
          int count = 0;
          int bytesProcessed = 0;
          rawKeys.reset();
          while (!atEof && 
                 bytesProcessed < memoryLimit && count < recordLimit) {

            // Read a record into buffer
            // Note: Attempt to re-use 'rawValue' as far as possible
            int keyOffset = rawKeys.getLength();       
            ValueBytes rawValue = 
              (count == keyOffsets.length || rawValues[count] == null) ? 
              in.createValueBytes() : 
              rawValues[count];
            int recordLength = in.nextRaw(rawKeys, rawValue);
            if (recordLength == -1) {
              in.close();
              if (deleteInput) {
                fs.delete(inFiles[currentFile]);
              }
              currentFile += 1;
              atEof = currentFile >= inFiles.length;
              if (!atEof) {
                in = new Reader(fs, inFiles[currentFile], conf);
              } else {
                in = null;
              }
              continue;
            }
            //int length = buffer.getLength() - start;
            int keyLength = rawKeys.getLength() - keyOffset;

            if (count == keyOffsets.length)
              grow();

            keyOffsets[count] = keyOffset;                // update pointers
            pointers[count] = count;
            keyLengths[count] = keyLength;
            rawValues[count] = rawValue;

            bytesProcessed += recordLength; 
            count++;
          }

          // buffer is full -- sort & flush it
          LOG.debug("flushing segment " + segments);
          rawBuffer = rawKeys.getData();
          sort(count);
          flush(count, bytesProcessed, isCompressed, isBlockCompressed, codec, 
                segments==0 && atEof);
          segments++;
        }
        return segments;
      }

      public void close() throws IOException {
        if (in != null) {
          in.close();
        }
        if (out != null) {
          out.close();
        }
        if (indexOut != null) {
          indexOut.close();
        }
      }

      private void grow() {
        int newLength = keyOffsets.length * 3 / 2;
        keyOffsets = grow(keyOffsets, newLength);
        pointers = grow(pointers, newLength);
        pointersCopy = new int[newLength];
        keyLengths = grow(keyLengths, newLength);
        rawValues = grow(rawValues, newLength);
      }

      private int[] grow(int[] old, int newLength) {
        int[] result = new int[newLength];
        System.arraycopy(old, 0, result, 0, old.length);
        return result;
      }
      
      private ValueBytes[] grow(ValueBytes[] old, int newLength) {
        ValueBytes[] result = new ValueBytes[newLength];
        System.arraycopy(old, 0, result, 0, old.length);
        for (int i=old.length; i < newLength; ++i) {
          result[i] = null;
        }
        return result;
      }

      private void flush(int count, int bytesProcessed, boolean isCompressed, 
                         boolean isBlockCompressed, CompressionCodec codec, boolean done) 
        throws IOException {
        if (out == null) {
          outName = done ? outFile : outFile.suffix(".0");
          out = fs.create(outName);
          if (!done) {
            indexOut = fs.create(outName.suffix(".index"));
          }
        }

        long segmentStart = out.getPos();
        Writer writer = createWriter(conf, out, keyClass, valClass, 
                                     isCompressed, isBlockCompressed, codec);
        
        if (!done) {
          writer.sync = null;                     // disable sync on temp files
        }

        for (int i = 0; i < count; i++) {         // write in sorted order
          int p = pointers[i];
          writer.appendRaw(rawBuffer, keyOffsets[p], keyLengths[p], rawValues[p]);
        }
        writer.sync();
        writer.out.flush();
        
        
        if (!done) {
          // Save the segment length
          WritableUtils.writeVLong(indexOut, segmentStart);
          WritableUtils.writeVLong(indexOut, (writer.out.getPos()-segmentStart));
          indexOut.flush();
        }
      }

      private void sort(int count) {
        System.arraycopy(pointers, 0, pointersCopy, 0, count);
        mergeSort.mergeSort(pointersCopy, pointers, 0, count);
      }
      class SeqFileComparator implements Comparator<IntWritable> {
        public int compare(IntWritable I, IntWritable J) {
          return comparator.compare(rawBuffer, keyOffsets[I.get()], 
                                    keyLengths[I.get()], rawBuffer, 
                                    keyOffsets[J.get()], keyLengths[J.get()]);
        }
      }
    } // SequenceFile.Sorter.SortPass

    /** The interface to iterate over raw keys/values of SequenceFiles. */
    public static interface RawKeyValueIterator {
      /** Gets the current raw key
       * @return DataOutputBuffer
       * @throws IOException
       */
      DataOutputBuffer getKey() throws IOException; 
      /** Gets the current raw value
       * @return ValueBytes 
       * @throws IOException
       */
      ValueBytes getValue() throws IOException; 
      /** Sets up the current key and value (for getKey and getValue)
       * @return true if there exists a key/value, false otherwise 
       * @throws IOException
       */
      boolean next() throws IOException;
      /** closes the iterator so that the underlying streams can be closed
       * @throws IOException
       */
      void close() throws IOException;
      /** Gets the Progress object; this has a float (0.0 - 1.0) 
       * indicating the bytes processed by the iterator so far
       */
      Progress getProgress();
    }    
    
    /**
     * Merges the list of segments of type <code>SegmentDescriptor</code>
     * @param segments the list of SegmentDescriptors
     * @param tmpDir the directory to write temporary files into
     * @return RawKeyValueIterator
     * @throws IOException
     */
    public RawKeyValueIterator merge(List <SegmentDescriptor> segments, 
                                     Path tmpDir) 
      throws IOException {
      MergeQueue mQueue = new MergeQueue(segments, tmpDir);
      return mQueue.merge();
    }

    /**
     * Merges the contents of files passed in Path[] using a max factor value
     * that is already set
     * @param inNames the array of path names
     * @param deleteInputs true if the input files should be deleted when 
     * unnecessary
     * @param tmpDir the directory to write temporary files into
     * @return RawKeyValueIteratorMergeQueue
     * @throws IOException
     */
    public RawKeyValueIterator merge(Path [] inNames, boolean deleteInputs,
                                     Path tmpDir) 
      throws IOException {
      return merge(inNames, deleteInputs, 
                   (inNames.length < factor) ? inNames.length : factor,
                   tmpDir);
    }

    /**
     * Merges the contents of files passed in Path[]
     * @param inNames the array of path names
     * @param deleteInputs true if the input files should be deleted when 
     * unnecessary
     * @param factor the factor that will be used as the maximum merge fan-in
     * @param tmpDir the directory to write temporary files into
     * @return RawKeyValueIteratorMergeQueue
     * @throws IOException
     */
    public RawKeyValueIterator merge(Path [] inNames, boolean deleteInputs,
                                     int factor, Path tmpDir) 
      throws IOException {
      //get the segments from inNames
      ArrayList <SegmentDescriptor> a = new ArrayList <SegmentDescriptor>();
      for (int i = 0; i < inNames.length; i++) {
        SegmentDescriptor s = new SegmentDescriptor(0, 
                                                    fs.getLength(inNames[i]), inNames[i]);
        s.preserveInput(!deleteInputs);
        s.doSync();
        a.add(s);
      }
      this.factor = factor;
      MergeQueue mQueue = new MergeQueue(a, tmpDir);
      return mQueue.merge();
    }

    /**
     * Merges the contents of files passed in Path[]
     * @param inNames the array of path names
     * @param tempDir the directory for creating temp files during merge
     * @param deleteInputs true if the input files should be deleted when 
     * unnecessary
     * @return RawKeyValueIteratorMergeQueue
     * @throws IOException
     */
    public RawKeyValueIterator merge(Path [] inNames, Path tempDir, 
                                     boolean deleteInputs) 
      throws IOException {
      //outFile will basically be used as prefix for temp files for the
      //intermediate merge outputs           
      this.outFile = new Path(tempDir + Path.SEPARATOR + "merged");
      //get the segments from inNames
      ArrayList <SegmentDescriptor> a = new ArrayList <SegmentDescriptor>();
      for (int i = 0; i < inNames.length; i++) {
        SegmentDescriptor s = new SegmentDescriptor(0, 
                                                    fs.getLength(inNames[i]), inNames[i]);
        s.preserveInput(!deleteInputs);
        s.doSync();
        a.add(s);
      }
      factor = (inNames.length < factor) ? inNames.length : factor;
      MergeQueue mQueue = new MergeQueue(a, tempDir);
      return mQueue.merge();
    }

    /**
     * Clones the attributes (like compression of the input file and creates a 
     * corresponding Writer
     * @param ignoredFileSys the (ignored) FileSystem object
     * @param inputFile the path of the input file whose attributes should be 
     * cloned 
     * @param outputFile the path of the output file 
     * @param prog the Progressable to report status during the file write
     * @return Writer
     * @throws IOException
     * @deprecated call  #cloneFileAttributes(Path,Path,Progressable) instead
     */
    public Writer cloneFileAttributes(FileSystem ignoredFileSys,
                                      Path inputFile, Path outputFile, Progressable prog) 
      throws IOException {
      return cloneFileAttributes(inputFile, outputFile, prog);
    }

    /**
     * Clones the attributes (like compression of the input file and creates a 
     * corresponding Writer
     * @param inputFile the path of the input file whose attributes should be 
     * cloned
     * @param outputFile the path of the output file 
     * @param prog the Progressable to report status during the file write
     * @return Writer
     * @throws IOException
     */
    public Writer cloneFileAttributes(Path inputFile, Path outputFile, 
                                      Progressable prog) throws IOException {
      FileSystem srcFileSys = inputFile.getFileSystem(conf);
      Reader reader = new Reader(srcFileSys, inputFile, 4096, conf);
      boolean compress = reader.isCompressed();
      boolean blockCompress = reader.isBlockCompressed();
      CompressionCodec codec = reader.getCompressionCodec();
      reader.close();
      
      FileSystem dstFileSys = outputFile.getFileSystem(conf);
      FSDataOutputStream out;
      if (prog != null)
        out = dstFileSys.create(outputFile, true, 
                                conf.getInt("io.file.buffer.size", 4096), prog);
      else
        out = dstFileSys.create(outputFile, true, 
                                conf.getInt("io.file.buffer.size", 4096));
      Writer writer = createWriter(conf, out, keyClass, valClass, compress, 
                                   blockCompress, codec);
      return writer;
    }

    /**
     * Writes records from RawKeyValueIterator into a file represented by the 
     * passed writer
     * @param records the RawKeyValueIterator
     * @param writer the Writer created earlier 
     * @throws IOException
     */
    public void writeFile(RawKeyValueIterator records, Writer writer) 
      throws IOException {
      while(records.next()) {
        writer.appendRaw(records.getKey().getData(), 0, 
                         records.getKey().getLength(), records.getValue());
      }
      writer.sync();
    }
        
    /** Merge the provided files.
     * @param inFiles the array of input path names
     * @param outFile the final output file
     * @throws IOException
     */
    public void merge(Path[] inFiles, Path outFile) throws IOException {
      if (fs.exists(outFile)) {
        throw new IOException("already exists: " + outFile);
      }
      RawKeyValueIterator r = merge(inFiles, false, outFile.getParent());
      Writer writer = cloneFileAttributes(inFiles[0], outFile, null);
      
      writeFile(r, writer);

      writer.close();
    }

    /** sort calls this to generate the final merged output */
    private int mergePass(Path tmpDir) throws IOException {
      LOG.debug("running merge pass");
      Writer writer = cloneFileAttributes(
                                          outFile.suffix(".0"), outFile, null);
      RawKeyValueIterator r = merge(outFile.suffix(".0"), 
                                    outFile.suffix(".0.index"), tmpDir);
      writeFile(r, writer);

      writer.close();
      return 0;
    }

    /** Used by mergePass to merge the output of the sort
     * @param inName the name of the input file containing sorted segments
     * @param indexIn the offsets of the sorted segments
     * @param tmpDir the relative directory to store intermediate results in
     * @return RawKeyValueIterator
     * @throws IOException
     */
    private RawKeyValueIterator merge(Path inName, Path indexIn, Path tmpDir) 
      throws IOException {
      //get the segments from indexIn
      //we create a SegmentContainer so that we can track segments belonging to
      //inName and delete inName as soon as we see that we have looked at all
      //the contained segments during the merge process & hence don't need 
      //them anymore
      SegmentContainer container = new SegmentContainer(inName, indexIn);
      MergeQueue mQueue = new MergeQueue(container.getSegmentList(), tmpDir);
      return mQueue.merge();
    }
    
    /** This class implements the core of the merge logic */
    private class MergeQueue extends PriorityQueue 
      implements RawKeyValueIterator {
      private boolean compress;
      private boolean blockCompress;
      private DataOutputBuffer rawKey = new DataOutputBuffer();
      private ValueBytes rawValue;
      private long totalBytesProcessed;
      private float progPerByte;
      private Progress mergeProgress = new Progress();
      private Path tmpDir;
      
      //a TreeMap used to store the segments sorted by size (segment offset and
      //segment path name is used to break ties between segments of same sizes)
      private Map<SegmentDescriptor, Void> sortedSegmentSizes =
        new TreeMap<SegmentDescriptor, Void>();
            
      public void put(SegmentDescriptor stream) throws IOException {
        if (size() == 0) {
          compress = stream.in.isCompressed();
          blockCompress = stream.in.isBlockCompressed();
        } else if (compress != stream.in.isCompressed() || 
                   blockCompress != stream.in.isBlockCompressed()) {
          throw new IOException("All merged files must be compressed or not.");
        } 
        super.put(stream);
      }
      
      /**
       * A queue of file segments to merge
       * @param segments the file segments to merge
       * @param tmpDir a relative local directory to save intermediate files in
       */
      public MergeQueue(List <SegmentDescriptor> segments,
                        Path tmpDir) {
        int size = segments.size();
        for (int i = 0; i < size; i++) {
          sortedSegmentSizes.put(segments.get(i), null);
        }
        this.tmpDir = tmpDir;
      }
      protected boolean lessThan(Object a, Object b) {
        SegmentDescriptor msa = (SegmentDescriptor)a;
        SegmentDescriptor msb = (SegmentDescriptor)b;
        return comparator.compare(msa.getKey().getData(), 0, 
                                  msa.getKey().getLength(), msb.getKey().getData(), 0, 
                                  msb.getKey().getLength()) < 0;
      }
      public void close() throws IOException {
        SegmentDescriptor ms;                           // close inputs
        while ((ms = (SegmentDescriptor)pop()) != null) {
          ms.cleanup();
        }
      }
      public DataOutputBuffer getKey() throws IOException {
        return rawKey;
      }
      public ValueBytes getValue() throws IOException {
        return rawValue;
      }
      public boolean next() throws IOException {
        if (size() == 0)
          return false;
        SegmentDescriptor ms = (SegmentDescriptor)top();
        //save the raw key
        rawKey.reset();
        rawKey.write(ms.getKey().getData(), 0, ms.getKey().getLength());
        //load the raw value. Re-use the existing rawValue buffer
        if (rawValue == null)
          rawValue = ms.in.createValueBytes();
        int valLength = ms.nextRawValue(rawValue);

        if (ms.nextRawKey()) {
          adjustTop();
        } else {
          pop();
          ms.cleanup();
        }
        if (progPerByte > 0) {
          totalBytesProcessed += rawKey.getLength() + valLength;
          mergeProgress.set(totalBytesProcessed * progPerByte);
        }
        return true;
      }
      
      public Progress getProgress() {
        return mergeProgress; 
      }

      /** This is the single level merge that is called multiple times 
       * depending on the factor size and the number of segments
       * @return RawKeyValueIterator
       * @throws IOException
       */
      public RawKeyValueIterator merge() throws IOException {
        //create the MergeStreams from the sorted map created in the constructor
        //and dump the final output to a file
        int numSegments = sortedSegmentSizes.size();
        int origFactor = factor;
        int passNo = 1;
        LocalDirAllocator lDirAlloc = new LocalDirAllocator("mapred.local.dir");
        do {
          //get the factor for this pass of merge
          factor = getPassFactor(passNo, numSegments);
          List<SegmentDescriptor> segmentsToMerge =
            new ArrayList<SegmentDescriptor>();
          int segmentsConsidered = 0;
          int numSegmentsToConsider = factor;
          while (true) {
            //extract the smallest 'factor' number of segment pointers from the 
            //TreeMap. Call cleanup on the empty segments (no key/value data)
            SegmentDescriptor[] mStream = 
              getSegmentDescriptors(numSegmentsToConsider);
            for (int i = 0; i < mStream.length; i++) {
              if (mStream[i].nextRawKey()) {
                segmentsToMerge.add(mStream[i]);
                segmentsConsidered++;
              }
              else {
                mStream[i].cleanup();
                numSegments--; //we ignore this segment for the merge
              }
            }
            //if we have the desired number of segments
            //or looked at all available segments, we break
            if (segmentsConsidered == factor || 
                sortedSegmentSizes.size() == 0) {
              break;
            }
              
            numSegmentsToConsider = factor - segmentsConsidered;
          }
          //feed the streams to the priority queue
          initialize(segmentsToMerge.size()); clear();
          for (int i = 0; i < segmentsToMerge.size(); i++) {
            put(segmentsToMerge.get(i));
          }
          //if we have lesser number of segments remaining, then just return the
          //iterator, else do another single level merge
          if (numSegments <= factor) {
            //calculate the length of the remaining segments. Required for 
            //calculating the merge progress
            long totalBytes = 0;
            for (int i = 0; i < segmentsToMerge.size(); i++) {
              totalBytes += segmentsToMerge.get(i).segmentLength;
            }
            if (totalBytes != 0) //being paranoid
              progPerByte = 1.0f / (float)totalBytes;
            //reset factor to what it originally was
            factor = origFactor;
            return this;
          } else {
            //we want to spread the creation of temp files on multiple disks if 
            //available under the space constraints
            long approxOutputSize = 0; 
            for (SegmentDescriptor s : segmentsToMerge) {
              approxOutputSize += s.segmentLength + 
                                  ChecksumFileSystem.getApproxChkSumLength(
                                  s.segmentLength);
            }
            Path tmpFilename = 
              new Path(tmpDir, "intermediate").suffix("." + passNo);

            Path outputFile =  lDirAlloc.getLocalPathForWrite(
                                                tmpFilename.toString(),
                                                approxOutputSize, conf);
            LOG.info("writing intermediate results to " + outputFile);
            Writer writer = cloneFileAttributes(
                                                fs.makeQualified(segmentsToMerge.get(0).segmentPathName), 
                                                fs.makeQualified(outputFile), null);
            writer.sync = null; //disable sync for temp files
            writeFile(this, writer);
            writer.close();
            
            //we finished one single level merge; now clean up the priority 
            //queue
            this.close();
            
            SegmentDescriptor tempSegment = 
              new SegmentDescriptor(0, fs.getLength(outputFile), outputFile);
            //put the segment back in the TreeMap
            sortedSegmentSizes.put(tempSegment, null);
            numSegments = sortedSegmentSizes.size();
            passNo++;
          }
          //we are worried about only the first pass merge factor. So reset the 
          //factor to what it originally was
          factor = origFactor;
        } while(true);
      }
  
      //Hadoop-591
      public int getPassFactor(int passNo, int numSegments) {
        if (passNo > 1 || numSegments <= factor || factor == 1) 
          return factor;
        int mod = (numSegments - 1) % (factor - 1);
        if (mod == 0)
          return factor;
        return mod + 1;
      }
      
      /** Return (& remove) the requested number of segment descriptors from the
       * sorted map.
       */
      public SegmentDescriptor[] getSegmentDescriptors(int numDescriptors) {
        if (numDescriptors > sortedSegmentSizes.size())
          numDescriptors = sortedSegmentSizes.size();
        SegmentDescriptor[] SegmentDescriptors = 
          new SegmentDescriptor[numDescriptors];
        Iterator iter = sortedSegmentSizes.keySet().iterator();
        int i = 0;
        while (i < numDescriptors) {
          SegmentDescriptors[i++] = (SegmentDescriptor)iter.next();
          iter.remove();
        }
        return SegmentDescriptors;
      }
    } // SequenceFile.Sorter.MergeQueue

    /** This class defines a merge segment. This class can be subclassed to 
     * provide a customized cleanup method implementation. In this 
     * implementation, cleanup closes the file handle and deletes the file 
     */
    public class SegmentDescriptor implements Comparable {
      
      long segmentOffset; //the start of the segment in the file
      long segmentLength; //the length of the segment
      Path segmentPathName; //the path name of the file containing the segment
      boolean ignoreSync = true; //set to true for temp files
      private Reader in = null; 
      private DataOutputBuffer rawKey = null; //this will hold the current key
      private boolean preserveInput = false; //delete input segment files?
      
      /** Constructs a segment
       * @param segmentOffset the offset of the segment in the file
       * @param segmentLength the length of the segment
       * @param segmentPathName the path name of the file containing the segment
       */
      public SegmentDescriptor (long segmentOffset, long segmentLength, 
                                Path segmentPathName) {
        this.segmentOffset = segmentOffset;
        this.segmentLength = segmentLength;
        this.segmentPathName = segmentPathName;
      }
      
      /** Do the sync checks */
      public void doSync() {ignoreSync = false;}
      
      /** Whether to delete the files when no longer needed */
      public void preserveInput(boolean preserve) {
        preserveInput = preserve;
      }

      public boolean shouldPreserveInput() {
        return preserveInput;
      }
      
      public int compareTo(Object o) {
        SegmentDescriptor that = (SegmentDescriptor)o;
        if (this.segmentLength != that.segmentLength) {
          return (this.segmentLength < that.segmentLength ? -1 : 1);
        }
        if (this.segmentOffset != that.segmentOffset) {
          return (this.segmentOffset < that.segmentOffset ? -1 : 1);
        }
        return (this.segmentPathName.toString()).
          compareTo(that.segmentPathName.toString());
      }

      public boolean equals(Object o) {
        if (!(o instanceof SegmentDescriptor)) {
          return false;
        }
        SegmentDescriptor that = (SegmentDescriptor)o;
        if (this.segmentLength == that.segmentLength &&
            this.segmentOffset == that.segmentOffset &&
            this.segmentPathName.toString().equals(
              that.segmentPathName.toString())) {
          return true;
        }
        return false;
      }

      public int hashCode() {
        return 37 * 17 + (int) (segmentOffset^(segmentOffset>>>32));
      }

      /** Fills up the rawKey object with the key returned by the Reader
       * @return true if there is a key returned; false, otherwise
       * @throws IOException
       */
      public boolean nextRawKey() throws IOException {
        if (in == null) {
          int bufferSize = conf.getInt("io.file.buffer.size", 4096); 
          if (fs.getUri().getScheme().startsWith("ramfs")) {
            bufferSize = conf.getInt("io.bytes.per.checksum", 512);
          }
          Reader reader = new Reader(fs, segmentPathName, 
                                     bufferSize, segmentOffset, 
                                     segmentLength, conf);
        
          //sometimes we ignore syncs especially for temp merge files
          if (ignoreSync) reader.sync = null;

          if (reader.keyClass != keyClass)
            throw new IOException("wrong key class: " + reader.getKeyClass() +
                                  " is not " + keyClass);
          if (reader.valClass != valClass)
            throw new IOException("wrong value class: "+reader.getValueClass()+
                                  " is not " + valClass);
          this.in = reader;
          rawKey = new DataOutputBuffer();
        }
        rawKey.reset();
        int keyLength = 
          in.nextRawKey(rawKey);
        return (keyLength >= 0);
      }

      /** Fills up the passed rawValue with the value corresponding to the key
       * read earlier
       * @param rawValue
       * @return the length of the value
       * @throws IOException
       */
      public int nextRawValue(ValueBytes rawValue) throws IOException {
        int valLength = in.nextRawValue(rawValue);
        return valLength;
      }
      
      /** Returns the stored rawKey */
      public DataOutputBuffer getKey() {
        return rawKey;
      }
      
      /** closes the underlying reader */
      private void close() throws IOException {
        this.in.close();
        this.in = null;
      }

      /** The default cleanup. Subclasses can override this with a custom 
       * cleanup 
       */
      public void cleanup() throws IOException {
        close();
        if (!preserveInput) {
          fs.delete(segmentPathName);
        }
      }
    } // SequenceFile.Sorter.SegmentDescriptor
    
    /** This class provisions multiple segments contained within a single
     *  file
     */
    private class LinkedSegmentsDescriptor extends SegmentDescriptor {

      SegmentContainer parentContainer = null;

      /** Constructs a segment
       * @param segmentOffset the offset of the segment in the file
       * @param segmentLength the length of the segment
       * @param segmentPathName the path name of the file containing the segment
       * @param parent the parent SegmentContainer that holds the segment
       */
      public LinkedSegmentsDescriptor (long segmentOffset, long segmentLength, 
                                       Path segmentPathName, SegmentContainer parent) {
        super(segmentOffset, segmentLength, segmentPathName);
        this.parentContainer = parent;
      }
      /** The default cleanup. Subclasses can override this with a custom 
       * cleanup 
       */
      public void cleanup() throws IOException {
        super.close();
        if (super.shouldPreserveInput()) return;
        parentContainer.cleanup();
      }
    } //SequenceFile.Sorter.LinkedSegmentsDescriptor

    /** The class that defines a container for segments to be merged. Primarily
     * required to delete temp files as soon as all the contained segments
     * have been looked at */
    private class SegmentContainer {
      private int numSegmentsCleanedUp = 0; //track the no. of segment cleanups
      private int numSegmentsContained; //# of segments contained
      private Path inName; //input file from where segments are created
      
      //the list of segments read from the file
      private ArrayList <SegmentDescriptor> segments = 
        new ArrayList <SegmentDescriptor>();
      /** This constructor is there primarily to serve the sort routine that 
       * generates a single output file with an associated index file */
      public SegmentContainer(Path inName, Path indexIn) throws IOException {
        //get the segments from indexIn
        FSDataInputStream fsIndexIn = fs.open(indexIn);
        long end = fs.getLength(indexIn);
        while (fsIndexIn.getPos() < end) {
          long segmentOffset = WritableUtils.readVLong(fsIndexIn);
          long segmentLength = WritableUtils.readVLong(fsIndexIn);
          Path segmentName = inName;
          segments.add(new LinkedSegmentsDescriptor(segmentOffset, 
                                                    segmentLength, segmentName, this));
        }
        fsIndexIn.close();
        fs.delete(indexIn);
        numSegmentsContained = segments.size();
        this.inName = inName;
      }

      public List <SegmentDescriptor> getSegmentList() {
        return segments;
      }
      public void cleanup() throws IOException {
        numSegmentsCleanedUp++;
        if (numSegmentsCleanedUp == numSegmentsContained) {
          fs.delete(inName);
        }
      }
    } //SequenceFile.Sorter.SegmentContainer

  } // SequenceFile.Sorter

} // SequenceFile
