001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.io;
019
020import org.apache.yetus.audience.InterfaceAudience;
021
022/**
023 * Implementations can be asked for an estimate of their size in bytes.
024 * <p>
025 * Useful for sizing caches. Its a given that implementation approximations do not account for 32 vs
026 * 64 bit nor for different VM implementations.
027 * <p>
028 * An Object's size is determined by the non-static data members in it, as well as the fixed
029 * {@link Object} overhead.
030 * <p>
031 * For example:
032 *
033 * <pre>
034 * public class SampleObject implements HeapSize {
035 *
036 *   int[] numbers;
037 *   int x;
038 * }
039 * </pre>
040 */
041@InterfaceAudience.Private
042public interface HeapSize {
043  /**
044   * Return the approximate 'exclusive deep size' of implementing object. Includes count of payload
045   * and hosting object sizings.
046   */
047  long heapSize();
048}