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1   /**
2    * Copyright 2011 The Apache Software Foundation
3    *
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *     http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing, software
15   * distributed under the License is distributed on an "AS IS" BASIS,
16   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17   * See the License for the specific language governing permissions and
18   * limitations under the License.
19   */
20  
21  package org.apache.hadoop.hbase.io.hfile;
22  
23  import java.nio.ByteBuffer;
24  import org.apache.hadoop.hbase.io.HeapSize;
25  import org.apache.hadoop.hbase.regionserver.metrics.SchemaMetrics;
26  
27  /**
28   * Cacheable is an interface that allows for an object to be cached. If using an
29   * on heap cache, just use heapsize. If using an off heap cache, Cacheable
30   * provides methods for serialization of the object.
31   *
32   * Some objects cannot be moved off heap, those objects will return a
33   * getSerializedLength() of 0.
34   *
35   */
36  public interface Cacheable extends HeapSize {
37    /**
38     * Returns the length of the ByteBuffer required to serialized the object. If the
39     * object cannot be serialized, it should also return 0.
40     *
41     * @return int length in bytes of the serialized form.
42     */
43  
44    public int getSerializedLength();
45  
46    /**
47     * Serializes its data into destination.
48     */
49    public void serialize(ByteBuffer destination);
50  
51    /**
52     * Returns CacheableDeserializer instance which reconstructs original object from ByteBuffer.
53     *
54     * @return CacheableDeserialzer instance.
55     */
56    public CacheableDeserializer<Cacheable> getDeserializer();
57  
58    /**
59     * @return the block type of this cached HFile block
60     */
61    public BlockType getBlockType();
62  
63    /**
64     * @return the metrics object identified by table and column family
65     */
66    public SchemaMetrics getSchemaMetrics();
67  
68  }