KijiTableSplit.java

/**
 * (c) Copyright 2012 WibiData, Inc.
 *
 * See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership.
 *
 * Licensed 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.kiji.mapreduce.impl;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.mapreduce.TableSplit;

import org.kiji.annotations.ApiAudience;

/**
 * An KijiTableSplit stores exactly the same data as TableSplit, but
 * does a better job handling default split sizes.
 */
@ApiAudience.Private
public final class KijiTableSplit extends TableSplit {
  private long mSplitSize; // lazily calculated and populated via getLength().

  /** The default constructor. */
  public KijiTableSplit() {
    super();
  }

  /**
   * Create a new KijiTableSplit instance from an HBase TableSplit.
   * @param tableSplit the HBase TableSplit to clone.
   */
  public KijiTableSplit(TableSplit tableSplit) {
    super(tableSplit.getTableName(), tableSplit.getStartRow(), tableSplit.getEndRow(),
        tableSplit.getRegionLocation());
  }

  /**
   * Returns the length of the split.
   *
   * This method does not currently examine the data in the region
   * represented by the split. We assume that each split is 3/4 full (where
   * "full" is defined as hbase.hregion.max.filesize). If the region had
   * that many bytes in it, it would split in two, each containing 1/2 that
   * many bytes. So we expect, on average, regions to be halfway between
   * "newly split" and "just about to split."
   *
   * @return the length of the split.
   * @see org.apache.hadoop.mapreduce.InputSplit#getLength()
   */
  @Override
  public long getLength() {
    if (0 == mSplitSize) {
      // Calculate this value once and memoize its result.
      Configuration conf = new Configuration();
      conf = HBaseConfiguration.addHbaseResources(conf);
      mSplitSize = (conf.getLong("hbase.hregion.max.filesize", 0) * 4) / 3;
      if (0 == mSplitSize) {
        // Set this to some reasonable non-zero default if the HBase properties
        // weren't set correctly.
        mSplitSize = 64 * 1024 * 1024; // 64 MB
      }
    }

    return mSplitSize;
  }
}