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1   /**
2    *
3    * Licensed to the Apache Software Foundation (ASF) under one
4    * or more contributor license agreements.  See the NOTICE file
5    * distributed with this work for additional information
6    * regarding copyright ownership.  The ASF licenses this file
7    * to you under the Apache License, Version 2.0 (the
8    * "License"); you may not use this file except in compliance
9    * with the License.  You may obtain a copy of the License at
10   *
11   *     http://www.apache.org/licenses/LICENSE-2.0
12   *
13   * Unless required by applicable law or agreed to in writing, software
14   * distributed under the License is distributed on an "AS IS" BASIS,
15   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16   * See the License for the specific language governing permissions and
17   * limitations under the License.
18   */
19  package org.apache.hadoop.hbase.master.normalizer;
20  
21  import java.util.List;
22  
23  import org.apache.hadoop.hbase.HBaseIOException;
24  import org.apache.hadoop.hbase.TableName;
25  import org.apache.hadoop.hbase.classification.InterfaceAudience;
26  import org.apache.hadoop.hbase.master.MasterServices;
27  
28  /**
29   * Performs "normalization" of regions on the cluster, making sure that suboptimal
30   * choice of split keys doesn't leave cluster in a situation when some regions are
31   * substantially larger than others for considerable amount of time.
32   *
33   * Users who want to use this feature could either use default {@link SimpleRegionNormalizer}
34   * or plug in their own implementation. Please note that overly aggressive normalization rules
35   * (attempting to make all regions perfectly equal in size) could potentially lead to
36   * "split/merge storms".
37   */
38  @InterfaceAudience.Private
39  public interface RegionNormalizer {
40    /**
41     * Set the master service. Must be called before first call to
42     * {@link #computePlanForTable(TableName)}.
43     * @param masterServices master services to use
44     */
45    void setMasterServices(MasterServices masterServices);
46  
47    /**
48     * Computes next optimal normalization plan.
49     * @param table table to normalize
50     * @return normalization actions to perform. Null if no action to take
51     */
52    List<NormalizationPlan> computePlanForTable(TableName table)
53        throws HBaseIOException;
54  }