lang/java/trevni/avro/src/main/java/org/apache/trevni/avro/AvroTrevniOutputFormat.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.trevni.avro;

import java.io.IOException;
import java.io.OutputStream;
import java.util.Map;

import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.Reporter;
import org.apache.hadoop.mapred.FileOutputFormat;
import org.apache.hadoop.mapred.RecordWriter;
import org.apache.hadoop.util.Progressable;

import org.apache.avro.Schema;
import org.apache.avro.reflect.ReflectData;
import org.apache.avro.mapred.AvroJob;
import org.apache.avro.mapred.AvroWrapper;

import org.apache.trevni.MetaData;
import org.apache.trevni.ColumnFileMetaData;

/** An {@link org.apache.hadoop.mapred.OutputFormat} that writes Avro data to
 * Trevni files.
 *
 * <p>Writes a directory of files per task, each comprising a single filesystem
 * block.  To reduce the number of files, increase the default filesystem block
 * size for the job.  Each task also requires enough memory to buffer a
 * filesystem block.
 */
public class AvroTrevniOutputFormat <T>
  extends FileOutputFormat<AvroWrapper<T>, NullWritable> {

  /** The file name extension for trevni files. */
  public final static String EXT = ".trv";

  public static final String META_PREFIX = "trevni.meta.";

  /** Add metadata to job output files.*/
  public static void setMeta(JobConf job, String key, String value) {
    job.set(META_PREFIX+key, value);
  }

  @Override
  public RecordWriter<AvroWrapper<T>, NullWritable>
    getRecordWriter(FileSystem ignore, final JobConf job,
                    final String name, Progressable prog)
    throws IOException {

    boolean isMapOnly = job.getNumReduceTasks() == 0;
    final Schema schema = isMapOnly
      ? AvroJob.getMapOutputSchema(job)
      : AvroJob.getOutputSchema(job);

    final ColumnFileMetaData meta = filterMetadata(job);

    final Path dir = FileOutputFormat.getTaskOutputPath(job, name);
    final FileSystem fs = dir.getFileSystem(job);
    if (!fs.mkdirs(dir))
      throw new IOException("Failed to create directory: " + dir);
    final long blockSize = fs.getDefaultBlockSize();

    return new RecordWriter<AvroWrapper<T>, NullWritable>() {
      private int part = 0;

      private AvroColumnWriter<T> writer =
        new AvroColumnWriter<T>(schema, meta, ReflectData.get());

      private void flush() throws IOException {
        OutputStream out = fs.create(new Path(dir, "part-"+(part++)+EXT));
        try {
          writer.writeTo(out);
        } finally {
          out.close();
        }
        writer = new AvroColumnWriter<T>(schema, meta, ReflectData.get());
      }

      public void write(AvroWrapper<T> wrapper, NullWritable ignore)
        throws IOException {
        writer.write(wrapper.datum());
        if (writer.sizeEstimate() >= blockSize)              // block full
          flush();
      }
      public void close(Reporter reporter) throws IOException {
        flush();
      }
    };
  }

   static ColumnFileMetaData filterMetadata(final JobConf job) {
    final ColumnFileMetaData meta = new ColumnFileMetaData();
    for (Map.Entry<String,String> e : job)
      if (e.getKey().startsWith(META_PREFIX))
        meta.put(e.getKey().substring(META_PREFIX.length()),
                 e.getValue().getBytes(MetaData.UTF8));
    return meta;
  }

}