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.io.hfile;
20
21 import com.google.common.collect.MinMaxPriorityQueue;
22
23 import org.apache.hadoop.hbase.classification.InterfaceAudience;
24 import org.apache.hadoop.hbase.io.HeapSize;
25
26 /**
27 * A memory-bound queue that will grow until an element brings
28 * total size >= maxSize. From then on, only entries that are sorted larger
29 * than the smallest current entry will be inserted/replaced.
30 *
31 * <p>Use this when you want to find the largest elements (according to their
32 * ordering, not their heap size) that consume as close to the specified
33 * maxSize as possible. Default behavior is to grow just above rather than
34 * just below specified max.
35 *
36 * <p>Object used in this queue must implement {@link HeapSize} as well as
37 * {@link Comparable}.
38 */
39 @InterfaceAudience.Private
40 public class LruCachedBlockQueue implements HeapSize {
41
42 private MinMaxPriorityQueue<LruCachedBlock> 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 LruCachedBlockQueue(long maxSize, long blockSize) {
52 int initialSize = (int)(maxSize / blockSize);
53 if(initialSize == 0) initialSize++;
54 queue = MinMaxPriorityQueue.expectedSize(initialSize).create();
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(LruCachedBlock cb) {
68 if(heapSize < maxSize) {
69 queue.add(cb);
70 heapSize += cb.heapSize();
71 } else {
72 LruCachedBlock 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 The next element in this queue, or {@code null} if the queue is
88 * empty.
89 */
90 public LruCachedBlock poll() {
91 return queue.poll();
92 }
93
94 /**
95 * @return The last element in this queue, or {@code null} if the queue is
96 * empty.
97 */
98 public LruCachedBlock pollLast() {
99 return queue.pollLast();
100 }
101
102 /**
103 * Total size of all elements in this queue.
104 * @return size of all elements currently in queue, in bytes
105 */
106 public long heapSize() {
107 return heapSize;
108 }
109 }