在hadoop中读取文件作为单个记录

Question

我没有。对于小文件，我想使用CombineFileInputFormat合并文件，以便每个文件数据作为MR作业中的单个记录出现。我遵循了html" target="_blank">http://yaseminavcular.blogspot.in/2011/03/many-
small-input-files.html
并尝试将其转换为新的api

我面临2个问题：

a）我只是用2个小文件对其进行测试，但仍然触发了2个映射器。我预期1

b）每行都将作为单个记录，我希望将整个文件作为单个记录。

这可能很痛苦，但是请查看下面的代码。我还是hadoop的天真

驾驶舱

public class MRDriver  extends Configured implements Tool {


@Override
public int run(String[] args) throws Exception {
    FileSystem fs = new Path(".").getFileSystem(getConf());
    fs.printStatistics();
    Job job = new Job(getConf());
    job.setJobName("Enron MR");
    job.setMapperClass(EnronMailReadMapper.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);
    job.setNumReduceTasks(0);
    job.setJarByClass(EnronMailReadMapper.class);
    RawCombineFileInputFormat.addInputPath(job, new Path(args[0]));
    job.setOutputFormatClass(TextOutputFormat.class);
    TextOutputFormat.setOutputPath(job, new Path(args[1]));
    return job.waitForCompletion(true) ? 0 :1;  
}

public static void main(String[] args) throws Exception  {
    int exitCode = ToolRunner.run(new MRDriver(), args);
    System.exit(exitCode);
}

}

下面的类主要是LineRecordReader的复制粘贴，其中包含对initialize（）和nextKeyValue（）函数的修改。

public class SingleFileRecordReader extends RecordReader<LongWritable, Text> {
  private static final Log LOG = LogFactory.getLog(SingleFileRecordReader.class);

  private long start;
  private long pos;
  private long end;
  private LineReader in;
  private int maxLineLength;
  private LongWritable key = null;
  private Text value = null;

  public void initialize(InputSplit genericSplit,
                         TaskAttemptContext context) throws IOException {
    FileSplit split = (FileSplit) genericSplit;
    Configuration job = context.getConfiguration();
    this.maxLineLength = job.getInt("mapred.linerecordreader.maxlength",
                                    Integer.MAX_VALUE);
    start = split.getStart();
    end = start + split.getLength();
    final Path file = split.getPath();

    // open the file and seek to the start of the split
    FileSystem fs = file.getFileSystem(job);
    FSDataInputStream fileIn = fs.open(split.getPath());

      fileIn.seek(start);
      in = new LineReader(fileIn, job);
    // If this is not the first split, we always throw away first record
    // because we always (except the last split) read one extra line in
    // next() method.
    if (start != 0) {
      start += in.readLine(new Text(), 0, maxBytesToConsume(start));
    }
    this.pos = start;
  }

  private int maxBytesToConsume(long pos) {
    return (int) Math.min(Integer.MAX_VALUE, end - pos);
  }

  private long getFilePosition() throws IOException {
    long retVal= pos;
    return retVal;
  }

  public boolean nextKeyValue() throws IOException {
    if (key == null) {
      key = new LongWritable();
    }
    key.set(pos);
    if (value == null) {
      value = new Text();
    }
    int newSize = 0;
    StringBuffer totalValue = new StringBuffer();
    // We always read one extra line, which lies outside the upper
    // split limit i.e. (end - 1)
    while (getFilePosition() <= end) {
      newSize = in.readLine(value, maxLineLength,
          Math.max(maxBytesToConsume(pos), maxLineLength));
      if (newSize == 0) {
        break;
      }
      totalValue.append(value.toString()+"\n");
      pos += newSize;
      if (newSize < maxLineLength) {
        break;
      }

      // line too long. try again
      LOG.info("Skipped line of size " + newSize + " at pos " + 
               (pos - newSize));
    }
    if (newSize == 0) {
      key = null;
      value = null;
      return false;
    } else {
        value = new Text(totalValue.toString());
      return true;
    }
  }

  @Override
  public LongWritable getCurrentKey() {
    return key;
  }

  @Override
  public Text getCurrentValue() {
    return value;
  }

  /**
   * Get the progress within the split
   */
  public float getProgress() throws IOException {
    if (start == end) {
      return 0.0f;
    } else {
      return Math.min(1.0f,
        (getFilePosition() - start) / (float)(end - start));
    }
  }

  public synchronized void close() throws IOException {
    try {
      if (in != null) {
        in.close();
      }
    } finally {

    }
  }

}

其他的文件

public class RawCombineFileInputFormat extends CombineFileInputFormat <LongWritable,Text>{

@Override
public RecordReader<LongWritable, Text> createRecordReader(
        InputSplit split, TaskAttemptContext context) throws IOException {
    return new CombineFileRecordReader< LongWritable, Text >((CombineFileSplit) split, context, MultiFileRecordReader.class);
}

}

和

public class MultiFileRecordReader extends RecordReader < LongWritable, Text > {

 private CombineFileSplit split;
 private TaskAttemptContext context;
 private int index;
 private RecordReader< LongWritable, Text > rr;

public MultiFileRecordReader(CombineFileSplit split, TaskAttemptContext context, Integer index) {
    this.split = split;
    this.context = context;
    this.index = index;
    this.rr = new SingleFileRecordReader();
}
@Override
public void initialize(InputSplit split, TaskAttemptContext context)
        throws IOException, InterruptedException {
    this.split = (CombineFileSplit) split;
      this.context = context;

      if (null == rr) {
       rr = new SingleFileRecordReader();
      }

      FileSplit fileSplit = new FileSplit(this.split.getPath(index), 
                                          this.split.getOffset(index), 
                                          this.split.getLength(index), 
                                          this.split.getLocations());
      this.rr.initialize(fileSplit, this.context);

}

@Override
public boolean nextKeyValue() throws IOException, InterruptedException {
    // TODO Auto-generated method stub
    return this.rr.nextKeyValue();
}

@Override
public LongWritable getCurrentKey() throws IOException, InterruptedException {
    // TODO Auto-generated method stub
    return this.rr.getCurrentKey();
}

@Override
public Text getCurrentValue() throws IOException, InterruptedException {
    // TODO Auto-generated method stub
    return this.rr.getCurrentValue();
}

@Override
public float getProgress() throws IOException, InterruptedException {
    // TODO Auto-generated method stub
    return this.rr.getProgress();
}

@Override
public void close() throws IOException {
    if (rr != null) {
           rr.close();
           rr = null;
    }       
}

}

Answer 1

看一下这种输入格式，这是一种在单个映射任务中读取多个文件的输入格式，传递给映射器的每条记录都会读取一个（未拆分）文件。WholeFileRecordReader负责将一个文件内容作为一个值发送。返回的键是NullWritable，值是每个文件整体的内容。现在，您可以使用它来运行mapreduce作业，并查看实际运行了多少个mapper并检查您得到的输出是否正确。

记录是根据WholeFileRecordReaders构造的。

    public class WholeFileInputFormat extends CombineFileInputFormat<NullWritable, Text>{

        @Override
        protected boolean isSplitable(JobContext context, Path file) {
            return false;
        }

/**
   * Creates a CombineFileRecordReader to read each file assigned to this InputSplit.
   * Note, that unlike ordinary InputSplits, split must be a CombineFileSplit, and therefore
   * is expected to specify multiple files.
   *
   * @param split The InputSplit to read.  Throws an IllegalArgumentException if this is
   *        not a CombineFileSplit.
   * @param context The context for this task.
   * @return a CombineFileRecordReader to process each file in split.
   *         It will read each file with a WholeFileRecordReader.
   * @throws IOException if there is an error.
   */

    @Override
    public RecordReader<NullWritable, Text> createRecordReader(
            InputSplit split, TaskAttemptContext context) throws IOException {

        if (!(split instanceof CombineFileSplit)) {
              throw new IllegalArgumentException("split must be a CombineFileSplit");
            }
            return new CombineFileRecordReader<NullWritable, Text>((CombineFileSplit) split, context, WholeFileRecordReader.class);
    }

    }

在上面可以使用WholeFileRecordReader，如下所示：

public class WholeFileRecordReader extends RecordReader<NullWritable, Text> {
    private static final Logger LOG = Logger.getLogger(WholeFileRecordReader.class);

      /** The path to the file to read. */
      private final Path mFileToRead;
      /** The length of this file. */
      private final long mFileLength;

      /** The Configuration. */
      private final Configuration mConf;

      /** Whether this FileSplit has been processed. */
      private boolean mProcessed;
      /** Single Text to store the file name of the current file. */
    //  private final Text mFileName;
      /** Single Text to store the value of this file (the value) when it is read. */
      private final Text mFileText;

      /**
       * Implementation detail: This constructor is built to be called via
       * reflection from within CombineFileRecordReader.
       *
       * @param fileSplit The CombineFileSplit that this will read from.
       * @param context The context for this task.
       * @param pathToProcess The path index from the CombineFileSplit to process in this record.
       */
      public WholeFileRecordReader(CombineFileSplit fileSplit, TaskAttemptContext context,
          Integer pathToProcess) {
        mProcessed = false;
        mFileToRead = fileSplit.getPath(pathToProcess);
        mFileLength = fileSplit.getLength(pathToProcess);
        mConf = context.getConfiguration();

        assert 0 == fileSplit.getOffset(pathToProcess);
        if (LOG.isDebugEnabled()) {
          LOG.debug("FileToRead is: " + mFileToRead.toString());
          LOG.debug("Processing path " + pathToProcess + " out of " + fileSplit.getNumPaths());

          try {
            FileSystem fs = FileSystem.get(mConf);
            assert fs.getFileStatus(mFileToRead).getLen() == mFileLength;
          } catch (IOException ioe) {
            // oh well, I was just testing.
          }
        }

    //    mFileName = new Text();
        mFileText = new Text();
      }

      /** {@inheritDoc} */
      @Override
      public void close() throws IOException {
        mFileText.clear();
      }

      /**
       * Returns the absolute path to the current file.
       *
       * @return The absolute path to the current file.
       * @throws IOException never.
       * @throws InterruptedException never.
       */
      @Override
      public NullWritable getCurrentKey() throws IOException, InterruptedException {
        return NullWritable.get();
      }

      /**
       * <p>Returns the current value.  If the file has been read with a call to NextKeyValue(),
       * this returns the contents of the file as a BytesWritable.  Otherwise, it returns an
       * empty BytesWritable.</p>
       *
       * <p>Throws an IllegalStateException if initialize() is not called first.</p>
       *
       * @return A BytesWritable containing the contents of the file to read.
       * @throws IOException never.
       * @throws InterruptedException never.
       */
      @Override
      public Text getCurrentValue() throws IOException, InterruptedException {
        return mFileText;
      }

      /**
       * Returns whether the file has been processed or not.  Since only one record
       * will be generated for a file, progress will be 0.0 if it has not been processed,
       * and 1.0 if it has.
       *
       * @return 0.0 if the file has not been processed.  1.0 if it has.
       * @throws IOException never.
       * @throws InterruptedException never.
       */
      @Override
      public float getProgress() throws IOException, InterruptedException {
        return (mProcessed) ? (float) 1.0 : (float) 0.0;
      }

      /**
       * All of the internal state is already set on instantiation.  This is a no-op.
       *
       * @param split The InputSplit to read.  Unused.
       * @param context The context for this task.  Unused.
       * @throws IOException never.
       * @throws InterruptedException never.
       */
      @Override
      public void initialize(InputSplit split, TaskAttemptContext context)
          throws IOException, InterruptedException {
        // no-op.
      }

      /**
       * <p>If the file has not already been read, this reads it into memory, so that a call
       * to getCurrentValue() will return the entire contents of this file as Text,
       * and getCurrentKey() will return the qualified path to this file as Text.  Then, returns
       * true.  If it has already been read, then returns false without updating any internal state.</p>
       *
       * @return Whether the file was read or not.
       * @throws IOException if there is an error reading the file.
       * @throws InterruptedException if there is an error.
       */
      @Override
      public boolean nextKeyValue() throws IOException, InterruptedException {
        if (!mProcessed) {
          if (mFileLength > (long) Integer.MAX_VALUE) {
            throw new IOException("File is longer than Integer.MAX_VALUE.");
          }
          byte[] contents = new byte[(int) mFileLength];

          FileSystem fs = mFileToRead.getFileSystem(mConf);
          FSDataInputStream in = null;
          try {
            // Set the contents of this file.
            in = fs.open(mFileToRead);
            IOUtils.readFully(in, contents, 0, contents.length);
            mFileText.set(contents, 0, contents.length);

          } finally {
            IOUtils.closeStream(in);
          }
          mProcessed = true;
          return true;
        }
        return false;
      }

}

以下是您的驱动程序代码：-

public int run(String[] arg) throws Exception {
    Configuration conf=getConf();
    FileSystem fs = FileSystem.get(conf);
    //estimate reducers
    Job job = new Job(conf);
    job.setJarByClass(WholeFileDriver.class);
    job.setJobName("WholeFile");
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(Text.class);
    job.setInputFormatClass(WholeFileInputFormat.class);
    job.setMapperClass(WholeFileMapper.class);
    job.setNumReduceTasks(0);

    FileInputFormat.addInputPath(job, new Path(arg[0]));
    Path output=new Path(arg[1]);
    try {
        fs.delete(output, true);
    } catch (IOException e) {
        LOG.warn("Failed to delete temporary path", e);
    }
    FileOutputFormat.setOutputPath(job, output);

    boolean ret=job.waitForCompletion(true);
    if(!ret){
        throw new Exception("Job Failed");
    }