/**
    * 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.hbase.regionserver;
  
  import java.util.Arrays;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  
  /**
   * A custom RegionSplitPolicy implementing a SplitPolicy that groups
   * rows by a prefix of the row-key
   *
   * This ensures that a region is not split "inside" a prefix of a row key.
   * I.e. rows can be co-located in a region by their prefix.
   */
  @InterfaceAudience.Private
  public class KeyPrefixRegionSplitPolicy extends IncreasingToUpperBoundRegionSplitPolicy {
    private static final Log LOG = LogFactory
        .getLog(KeyPrefixRegionSplitPolicy.class);
    @Deprecated
    public static final String PREFIX_LENGTH_KEY_DEPRECATED = "prefix_split_key_policy.prefix_length";
    public static final String PREFIX_LENGTH_KEY = "KeyPrefixRegionSplitPolicy.prefix_length";
  
    private int prefixLength = 0;
  
    @Override
    protected void configureForRegion(HRegion region) {
      super.configureForRegion(region);
      prefixLength = 0;
  
      // read the prefix length from the table descriptor
      String prefixLengthString = region.getTableDesc().getValue(
          PREFIX_LENGTH_KEY);
      if (prefixLengthString == null) {
        //read the deprecated value
        prefixLengthString = region.getTableDesc().getValue(PREFIX_LENGTH_KEY_DEPRECATED);
        if (prefixLengthString == null) {
          LOG.error(PREFIX_LENGTH_KEY + " not specified for table "
              + region.getTableDesc().getTableName()
              + ". Using default RegionSplitPolicy");
          return;
        }
      }
      try {
        prefixLength = Integer.parseInt(prefixLengthString);
      } catch (NumberFormatException nfe) {
        /* Differentiate NumberFormatException from an invalid value range reported below. */
        LOG.error("Number format exception when parsing " + PREFIX_LENGTH_KEY + " for table "
            + region.getTableDesc().getTableName() + ":"
            + prefixLengthString + ". " + nfe);
        return;
      }
      if (prefixLength <= 0) {
        LOG.error("Invalid value for " + PREFIX_LENGTH_KEY + " for table "
            + region.getTableDesc().getTableName() + ":"
            + prefixLengthString + ". Using default RegionSplitPolicy");
      }
    }
  
    @Override
    protected byte[] getSplitPoint() {
      byte[] splitPoint = super.getSplitPoint();
      if (prefixLength > 0 && splitPoint != null && splitPoint.length > 0) {
        // group split keys by a prefix
        return Arrays.copyOf(splitPoint,
            Math.min(prefixLength, splitPoint.length));
      } else {
        return splitPoint;
      }
    }
  }