1 /**
2 * Copyright 2009 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.hfile;
21
22 import java.util.LinkedList;
23 import java.util.PriorityQueue;
24
25 import org.apache.hadoop.hbase.io.HeapSize;
26
27 /**
28 * A memory-bound queue that will grow until an element brings
29 * total size >= maxSize. From then on, only entries that are sorted larger
30 * than the smallest current entry will be inserted/replaced.
31 *
32 * <p>Use this when you want to find the largest elements (according to their
33 * ordering, not their heap size) that consume as close to the specified
34 * maxSize as possible. Default behavior is to grow just above rather than
35 * just below specified max.
36 *
37 * <p>Object used in this queue must implement {@link HeapSize} as well as
38 * {@link Comparable}.
39 */
40 public class CachedBlockQueue implements HeapSize {
41
42 private PriorityQueue<CachedBlock> queue;
43
44 private long heapSize;
45 private long maxSize;
46
47 /**
48 * @param maxSize the target size of elements in the queue
49 * @param blockSize expected average size of blocks
50 */
51 public CachedBlockQueue(long maxSize, long blockSize) {
52 int initialSize = (int)(maxSize / blockSize);
53 if(initialSize == 0) initialSize++;
54 queue = new PriorityQueue<CachedBlock>(initialSize);
55 heapSize = 0;
56 this.maxSize = maxSize;
57 }
58
59 /**
60 * Attempt to add the specified cached block to this queue.
61 *
62 * <p>If the queue is smaller than the max size, or if the specified element
63 * is ordered before the smallest element in the queue, the element will be
64 * added to the queue. Otherwise, there is no side effect of this call.
65 * @param cb block to try to add to the queue
66 */
67 public void add(CachedBlock cb) {
68 if(heapSize < maxSize) {
69 queue.add(cb);
70 heapSize += cb.heapSize();
71 } else {
72 CachedBlock head = queue.peek();
73 if(cb.compareTo(head) > 0) {
74 heapSize += cb.heapSize();
75 heapSize -= head.heapSize();
76 if(heapSize > maxSize) {
77 queue.poll();
78 } else {
79 heapSize += head.heapSize();
80 }
81 queue.add(cb);
82 }
83 }
84 }
85
86 /**
87 * @return a sorted List of all elements in this queue, in descending order
88 */
89 public LinkedList<CachedBlock> get() {
90 LinkedList<CachedBlock> blocks = new LinkedList<CachedBlock>();
91 while (!queue.isEmpty()) {
92 blocks.addFirst(queue.poll());
93 }
94 return blocks;
95 }
96
97 /**
98 * Total size of all elements in this queue.
99 * @return size of all elements currently in queue, in bytes
100 */
101 public long heapSize() {
102 return heapSize;
103 }
104 }