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DWRF file format for Hive
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//  Copyright (c) 2013, Facebook, Inc.  All rights reserved.

/**
 * 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 com.facebook.hive.orc;

import com.facebook.hive.orc.compression.CompressionKind;
import com.facebook.hive.orc.statistics.ColumnStatistics;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.List;

/**
 * The interface for reading ORC files.
 *
 * One Reader can support multiple concurrent RecordReader.
 */
public interface Reader {

  /**
   * Get the number of rows in the file.
   * @return the number of rows
   */
  long getNumberOfRows();

  /**
   * Get the raw size of the data in the file
   * @return the raw size
   */
  long getRawDataSize();

  /**
   * Get the user metadata keys.
   * @return the set of metadata keys
   */
  Iterable getMetadataKeys();

  /**
   * Get a user metadata value.
   * @param key a key given by the user
   * @return the bytes associated with the given key
   */
  ByteBuffer getMetadataValue(String key);

  /**
   * Get the compression kind.
   * @return the kind of compression in the file
   */
  CompressionKind getCompression();

  /**
   * Get the buffer size for the compression.
   * @return number of bytes to buffer for the compression codec.
   */
  int getCompressionSize();

  /**
   * Get the number of rows per a entry in the row index.
   * @return the number of rows per an entry in the row index or 0 if there
   * is no row index.
   */
  int getRowIndexStride();

  /**
   * Get the list of stripes.
   * @return the information about the stripes sorted in order of how they occur in the file physically.
   */
  Iterable getStripes();

  /**
   * Get the object inspector for looking at the objects.
   * @return an object inspector for each row returned
   */
  ObjectInspector getObjectInspector();

  /**
   * Get the length of the file.
   * @return the number of bytes in the file
   */
  long getContentLength();

  /**
   * Get the statistics about the columns in the file.
   * @return the information about the column
   */
  ColumnStatistics[] getStatistics();

  /**
   * Get the list of types contained in the file. The root type is the first
   * type in the list.
   * @return the list of flattened types
   */
  List getTypes();

  /**
   * Create a RecordReader that will scan the entire file.
   * @param include true for each column that should be included
   * @return A new RecordReader
   * @throws IOException
   */
  RecordReader rows(boolean[] include) throws IOException;

  /**
   * Create a RecordReader that will start reading at the first stripe after
   * offset up to the stripe that starts at offset + length. This is intended
   * to work with MapReduce's FileInputFormat where divisions are picked
   * blindly, but they must cover all of the rows.
   * @param offset a byte offset in the file
   * @param length a number of bytes in the file
   * @param include true for each column that should be included
   * @return a new RecordReader that will read the specified rows.
   * @throws IOException
   */
  RecordReader rows(long offset, long length,
                    boolean[] include) throws IOException;

  /**
   * Create a StripeReader that will start reading at the first stripe after
   * offset up to the stripe that starts at offset + length.
   * @param offset a byte offset in the file
   * @param length a number of bytes in the file
   * @return a new StripeReader that will read the specified stripes.
   * @throws IOException
   */
  StripeReader stripes(long offset, long length) throws IOException;

}