/**
* Copyright 2011 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.slab;
import java.nio.ByteBuffer;
import java.util.List;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicLong;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.io.HeapSize;
import org.apache.hadoop.hbase.io.hfile.BlockCache;
import org.apache.hadoop.hbase.io.hfile.BlockCacheColumnFamilySummary;
import org.apache.hadoop.hbase.io.hfile.BlockCacheKey;
import org.apache.hadoop.hbase.io.hfile.CacheStats;
import org.apache.hadoop.hbase.io.hfile.Cacheable;
import org.apache.hadoop.hbase.io.hfile.CacheableDeserializer;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.hbase.util.ClassSize;
import org.apache.hadoop.util.StringUtils;
import com.google.common.collect.MapEvictionListener;
import com.google.common.collect.MapMaker;
/**
* SingleSizeCache is a slab allocated cache that caches elements up to a single
* size. It uses a slab allocator (Slab.java) to divide a direct bytebuffer,
* into evenly sized blocks. Any cached data will take up exactly 1 block. An
* exception will be thrown if the cached data cannot fit into the blockSize of
* this SingleSizeCache.
*
* Eviction and LRUness is taken care of by Guava's MapMaker, which creates a
* ConcurrentLinkedHashMap.
*
**/
public class SingleSizeCache implements BlockCache, HeapSize {
private final Slab backingStore;
private final ConcurrentMap<BlockCacheKey, CacheablePair> backingMap;
private final int numBlocks;
private final int blockSize;
private final CacheStats stats;
private final SlabItemActionWatcher actionWatcher;
private final AtomicLong size;
private final AtomicLong timeSinceLastAccess;
public final static long CACHE_FIXED_OVERHEAD = ClassSize
.align((2 * Bytes.SIZEOF_INT) + (5 * ClassSize.REFERENCE)
+ +ClassSize.OBJECT);
static final Log LOG = LogFactory.getLog(SingleSizeCache.class);
/**
* Default constructor. Specify the size of the blocks, number of blocks, and
* the SlabCache this cache will be assigned to.
*
*
* @param blockSize the size of each block, in bytes
*
* @param numBlocks the number of blocks of blockSize this cache will hold.
*
* @param master the SlabCache this SingleSlabCache is assigned to.
*/
public SingleSizeCache(int blockSize, int numBlocks,
SlabItemActionWatcher master) {
this.blockSize = blockSize;
this.numBlocks = numBlocks;
backingStore = new Slab(blockSize, numBlocks);
this.stats = new CacheStats();
this.actionWatcher = master;
this.size = new AtomicLong(CACHE_FIXED_OVERHEAD + backingStore.heapSize());
this.timeSinceLastAccess = new AtomicLong();
// This evictionListener is called whenever the cache automatically
// evicts
// something.
MapEvictionListener<BlockCacheKey, CacheablePair> listener = new MapEvictionListener<BlockCacheKey, CacheablePair>() {
@Override
public void onEviction(BlockCacheKey key, CacheablePair value) {
timeSinceLastAccess.set(System.nanoTime()
- value.recentlyAccessed.get());
stats.evict();
doEviction(key, value);
}
};
backingMap = new MapMaker().maximumSize(numBlocks - 1)
.evictionListener(listener).makeMap();
}
@Override
public void cacheBlock(BlockCacheKey blockName, Cacheable toBeCached) {
ByteBuffer storedBlock;
try {
storedBlock = backingStore.alloc(toBeCached.getSerializedLength());
} catch (InterruptedException e) {
LOG.warn("SlabAllocator was interrupted while waiting for block to become available");
LOG.warn(e);
return;
}
CacheablePair newEntry = new CacheablePair(toBeCached.getDeserializer(),
storedBlock);
toBeCached.serialize(storedBlock);
synchronized (this) {
CacheablePair alreadyCached = backingMap.putIfAbsent(blockName, newEntry);
if (alreadyCached != null) {
backingStore.free(storedBlock);
throw new RuntimeException("already cached " + blockName);
}
if (actionWatcher != null) {
actionWatcher.onInsertion(blockName, this);
}
}
newEntry.recentlyAccessed.set(System.nanoTime());
this.size.addAndGet(newEntry.heapSize());
}
@Override
public Cacheable getBlock(BlockCacheKey key, boolean caching) {
CacheablePair contentBlock = backingMap.get(key);
if (contentBlock == null) {
stats.miss(caching);
return null;
}
stats.hit(caching);
// If lock cannot be obtained, that means we're undergoing eviction.
try {
contentBlock.recentlyAccessed.set(System.nanoTime());
synchronized (contentBlock) {
if (contentBlock.serializedData == null) {
// concurrently evicted
LOG.warn("Concurrent eviction of " + key);
return null;
}
return contentBlock.deserializer
.deserialize(contentBlock.serializedData.asReadOnlyBuffer());
}
} catch (Throwable t) {
LOG.error("Deserializer threw an exception. This may indicate a bug.", t);
return null;
}
}
/**
* Evicts the block
*
* @param key the key of the entry we are going to evict
* @return the evicted ByteBuffer
*/
public boolean evictBlock(BlockCacheKey key) {
stats.evict();
CacheablePair evictedBlock = backingMap.remove(key);
if (evictedBlock != null) {
doEviction(key, evictedBlock);
}
return evictedBlock != null;
}
private void doEviction(BlockCacheKey key, CacheablePair evictedBlock) {
long evictedHeap = 0;
synchronized (evictedBlock) {
if (evictedBlock.serializedData == null) {
// someone else already freed
return;
}
evictedHeap = evictedBlock.heapSize();
ByteBuffer bb = evictedBlock.serializedData;
evictedBlock.serializedData = null;
backingStore.free(bb);
// We have to do this callback inside the synchronization here.
// Otherwise we can have the following interleaving:
// Thread A calls getBlock():
// SlabCache directs call to this SingleSizeCache
// It gets the CacheablePair object
// Thread B runs eviction
// doEviction() is called and sets serializedData = null, here.
// Thread A sees the null serializedData, and returns null
// Thread A calls cacheBlock on the same block, and gets
// "already cached" since the block is still in backingStore
if (actionWatcher != null) {
actionWatcher.onEviction(key, this);
}
}
stats.evicted();
size.addAndGet(-1 * evictedHeap);
}
public void logStats() {
long milliseconds = this.timeSinceLastAccess.get() / 1000000;
LOG.info("For Slab of size " + this.blockSize + ": "
+ this.getOccupiedSize() / this.blockSize
+ " occupied, out of a capacity of " + this.numBlocks
+ " blocks. HeapSize is "
+ StringUtils.humanReadableInt(this.heapSize()) + " bytes." + ", "
+ "churnTime=" + StringUtils.formatTime(milliseconds));
LOG.info("Slab Stats: " + "accesses="
+ stats.getRequestCount()
+ ", "
+ "hits="
+ stats.getHitCount()
+ ", "
+ "hitRatio="
+ (stats.getHitCount() == 0 ? "0" : (StringUtils.formatPercent(
stats.getHitRatio(), 2) + "%, "))
+ "cachingAccesses="
+ stats.getRequestCachingCount()
+ ", "
+ "cachingHits="
+ stats.getHitCachingCount()
+ ", "
+ "cachingHitsRatio="
+ (stats.getHitCachingCount() == 0 ? "0" : (StringUtils.formatPercent(
stats.getHitCachingRatio(), 2) + "%, ")) + "evictions="
+ stats.getEvictionCount() + ", " + "evicted="
+ stats.getEvictedCount() + ", " + "evictedPerRun="
+ stats.evictedPerEviction());
}
public void shutdown() {
backingStore.shutdown();
}
public long heapSize() {
return this.size.get() + backingStore.heapSize();
}
public long size() {
return (long) this.blockSize * (long) this.numBlocks;
}
public long getFreeSize() {
return (long) backingStore.getBlocksRemaining() * (long) blockSize;
}
public long getOccupiedSize() {
return (long) (numBlocks - backingStore.getBlocksRemaining()) * (long) blockSize;
}
public long getEvictedCount() {
return stats.getEvictedCount();
}
public CacheStats getStats() {
return this.stats;
}
@Override
public long getBlockCount() {
return numBlocks - backingStore.getBlocksRemaining();
}
/* Since its offheap, it doesn't matter if its in memory or not */
@Override
public void cacheBlock(BlockCacheKey cacheKey, Cacheable buf, boolean inMemory) {
this.cacheBlock(cacheKey, buf);
}
/*
* This is never called, as evictions are handled in the SlabCache layer,
* implemented in the event we want to use this as a standalone cache.
*/
@Override
public int evictBlocksByHfileName(String hfileName) {
int evictedCount = 0;
for (BlockCacheKey e : backingMap.keySet()) {
if (e.getHfileName().equals(hfileName)) {
this.evictBlock(e);
}
}
return evictedCount;
}
@Override
public long getCurrentSize() {
return 0;
}
/*
* Not implemented. Extremely costly to do this from the off heap cache, you'd
* need to copy every object on heap once
*/
@Override
public List<BlockCacheColumnFamilySummary> getBlockCacheColumnFamilySummaries(
Configuration conf) {
throw new UnsupportedOperationException();
}
/* Just a pair class, holds a reference to the parent cacheable */
private class CacheablePair implements HeapSize {
final CacheableDeserializer<Cacheable> deserializer;
ByteBuffer serializedData;
AtomicLong recentlyAccessed;
private CacheablePair(CacheableDeserializer<Cacheable> deserializer,
ByteBuffer serializedData) {
this.recentlyAccessed = new AtomicLong();
this.deserializer = deserializer;
this.serializedData = serializedData;
}
/*
* Heapsize overhead of this is the default object overhead, the heapsize of
* the serialized object, and the cost of a reference to the bytebuffer,
* which is already accounted for in SingleSizeCache
*/
@Override
public long heapSize() {
return ClassSize.align(ClassSize.OBJECT + ClassSize.REFERENCE * 3
+ ClassSize.ATOMIC_LONG);
}
}
}