/**
* Copyright The Apache Software Foundation
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with this
* work for additional information regarding copyright ownership. The ASF
* licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*/
package org.apache.hadoop.hbase.io.hfile.bucket;
import java.util.Comparator;
import java.util.Map;
import java.util.Map.Entry;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.io.hfile.BlockCacheKey;
import org.apache.hadoop.hbase.io.hfile.bucket.BucketCache.BucketEntry;
import com.google.common.collect.MinMaxPriorityQueue;
/**
* A memory-bound queue that will grow until an element brings total size larger
* than maxSize. From then on, only entries that are sorted larger than the
* smallest current entry will be inserted/replaced.
*
* <p>
* Use this when you want to find the largest elements (according to their
* ordering, not their heap size) that consume as close to the specified maxSize
* as possible. Default behavior is to grow just above rather than just below
* specified max.
*/
@InterfaceAudience.Private
public class CachedEntryQueue {
private MinMaxPriorityQueue<Map.Entry<BlockCacheKey, BucketEntry>> queue;
private long cacheSize;
private long maxSize;
/**
* @param maxSize the target size of elements in the queue
* @param blockSize expected average size of blocks
*/
public CachedEntryQueue(long maxSize, long blockSize) {
int initialSize = (int) (maxSize / blockSize);
if (initialSize == 0)
initialSize++;
queue = MinMaxPriorityQueue
.orderedBy(new Comparator<Map.Entry<BlockCacheKey, BucketEntry>>() {
public int compare(Entry<BlockCacheKey, BucketEntry> entry1,
Entry<BlockCacheKey, BucketEntry> entry2) {
return entry1.getValue().compareTo(entry2.getValue());
}
}).expectedSize(initialSize).create();
cacheSize = 0;
this.maxSize = maxSize;
}
/**
* Attempt to add the specified entry to this queue.
*
* <p>
* If the queue is smaller than the max size, or if the specified element is
* ordered after the smallest element in the queue, the element will be added
* to the queue. Otherwise, there is no side effect of this call.
* @param entry a bucket entry with key to try to add to the queue
*/
public void add(Map.Entry<BlockCacheKey, BucketEntry> entry) {
if (cacheSize < maxSize) {
queue.add(entry);
cacheSize += entry.getValue().getLength();
} else {
BucketEntry head = queue.peek().getValue();
if (entry.getValue().compareTo(head) > 0) {
cacheSize += entry.getValue().getLength();
cacheSize -= head.getLength();
if (cacheSize > maxSize) {
queue.poll();
} else {
cacheSize += head.getLength();
}
queue.add(entry);
}
}
}
/**
* @return The next element in this queue, or {@code null} if the queue is
* empty.
*/
public Map.Entry<BlockCacheKey, BucketEntry> poll() {
return queue.poll();
}
/**
* @return The last element in this queue, or {@code null} if the queue is
* empty.
*/
public Map.Entry<BlockCacheKey, BucketEntry> pollLast() {
return queue.pollLast();
}
/**
* Total size of all elements in this queue.
* @return size of all elements currently in queue, in bytes
*/
public long cacheSize() {
return cacheSize;
}
}