1 /**
2 * Copyright 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 package org.apache.hadoop.hbase.io;
21
22 import org.apache.hadoop.hbase.classification.InterfaceAudience;
23
24 /**
25 * Implementations can be asked for an estimate of their size in bytes.
26 * <p>
27 * Useful for sizing caches. Its a given that implementation approximations
28 * do not account for 32 vs 64 bit nor for different VM implementations.
29 * <p>
30 * An Object's size is determined by the non-static data members in it,
31 * as well as the fixed {@link Object} overhead.
32 * <p>
33 * For example:
34 * <pre>
35 * public class SampleObject implements HeapSize {
36 *
37 * int [] numbers;
38 * int x;
39 * }
40 * </pre>
41 */
42 @InterfaceAudience.Private
43 public interface HeapSize {
44 /**
45 * @return Approximate 'exclusive deep size' of implementing object. Includes
46 * count of payload and hosting object sizings.
47 */
48 long heapSize();
49 }