/*
* 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.solr.store.blockcache;
import java.nio.ByteBuffer;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.atomic.AtomicInteger;
import com.github.benmanes.caffeine.cache.Cache;
import com.github.benmanes.caffeine.cache.Caffeine;
import com.github.benmanes.caffeine.cache.RemovalCause;
import com.github.benmanes.caffeine.cache.RemovalListener;
/**
* @lucene.experimental
*/
public class BlockCache {
public static final int _128M = 134217728;
public static final int _32K = 32768;
private final Cache<BlockCacheKey,BlockCacheLocation> cache;
private final ByteBuffer[] banks;
private final BlockLocks[] locks;
private final AtomicInteger[] lockCounters;
private final int blockSize;
private final int numberOfBlocksPerBank;
private final int maxEntries;
private final Metrics metrics;
private final List<OnRelease> onReleases = new CopyOnWriteArrayList<>();
public static interface OnRelease {
public void release(BlockCacheKey blockCacheKey);
}
public BlockCache(Metrics metrics, boolean directAllocation, long totalMemory) {
this(metrics, directAllocation, totalMemory, _128M);
}
public BlockCache(Metrics metrics, boolean directAllocation,
long totalMemory, int slabSize) {
this(metrics, directAllocation, totalMemory, slabSize, _32K);
}
public BlockCache(Metrics metrics, boolean directAllocation,
long totalMemory, int slabSize, int blockSize) {
this.metrics = metrics;
numberOfBlocksPerBank = slabSize / blockSize;
int numberOfBanks = (int) (totalMemory / slabSize);
banks = new ByteBuffer[numberOfBanks];
locks = new BlockLocks[numberOfBanks];
lockCounters = new AtomicInteger[numberOfBanks];
maxEntries = (numberOfBlocksPerBank * numberOfBanks) - 1;
for (int i = 0; i < numberOfBanks; i++) {
if (directAllocation) {
banks[i] = ByteBuffer.allocateDirect(numberOfBlocksPerBank * blockSize);
} else {
banks[i] = ByteBuffer.allocate(numberOfBlocksPerBank * blockSize);
}
locks[i] = new BlockLocks(numberOfBlocksPerBank);
lockCounters[i] = new AtomicInteger();
}
RemovalListener<BlockCacheKey,BlockCacheLocation> listener = (blockCacheKey, blockCacheLocation, removalCause) -> releaseLocation(blockCacheKey, blockCacheLocation, removalCause);
cache = Caffeine.newBuilder()
.removalListener(listener)
.maximumSize(maxEntries)
.build();
this.blockSize = blockSize;
}
public void release(BlockCacheKey key) {
cache.invalidate(key);
}
private void releaseLocation(BlockCacheKey blockCacheKey, BlockCacheLocation location, RemovalCause removalCause) {
if (location == null) {
return;
}
int bankId = location.getBankId();
int block = location.getBlock();
// mark the block removed before we release the lock to allow it to be reused
location.setRemoved(true);
locks[bankId].clear(block);
lockCounters[bankId].decrementAndGet();
for (OnRelease onRelease : onReleases) {
onRelease.release(blockCacheKey);
}
if (removalCause.wasEvicted()) {
metrics.blockCacheEviction.incrementAndGet();
}
metrics.blockCacheSize.decrementAndGet();
}
/**
* This is only best-effort... it's possible for false to be returned, meaning the block was not able to be cached.
* NOTE: blocks may not currently be updated (false will be returned if the block is already cached)
* The blockCacheKey is cloned before it is inserted into the map, so it may be reused by clients if desired.
*
* @param blockCacheKey the key for the block
* @param blockOffset the offset within the block
* @param data source data to write to the block
* @param offset offset within the source data array
* @param length the number of bytes to write.
* @return true if the block was cached/updated
*/
public boolean store(BlockCacheKey blockCacheKey, int blockOffset,
byte[] data, int offset, int length) {
if (length + blockOffset > blockSize) {
throw new RuntimeException("Buffer size exceeded, expecting max ["
+ blockSize + "] got length [" + length + "] with blockOffset ["
+ blockOffset + "]");
}
BlockCacheLocation location = cache.getIfPresent(blockCacheKey);
if (location == null) {
location = new BlockCacheLocation();
if (!findEmptyLocation(location)) {
// YCS: it looks like when the cache is full (a normal scenario), then two concurrent writes will result in one of them failing
// because no eviction is done first. The code seems to rely on leaving just a single block empty.
// TODO: simplest fix would be to leave more than one block empty
metrics.blockCacheStoreFail.incrementAndGet();
return false;
}
} else {
// If we allocated a new block, then it has never been published and is thus never in danger of being concurrently removed.
// On the other hand, if this is an existing block we are updating, it may concurrently be removed and reused for another
// purpose (and then our write may overwrite that). This can happen even if clients never try to update existing blocks,
// since two clients can try to cache the same block concurrently. Because of this, the ability to update an existing
// block has been removed for the time being (see SOLR-10121).
// No metrics to update: we don't count a redundant store as a store fail.
return false;
}
int bankId = location.getBankId();
int bankOffset = location.getBlock() * blockSize;
ByteBuffer bank = getBank(bankId);
bank.position(bankOffset + blockOffset);
bank.put(data, offset, length);
// make sure all modifications to the block have been completed before we publish it.
cache.put(blockCacheKey.clone(), location);
metrics.blockCacheSize.incrementAndGet();
return true;
}
/**
* @param blockCacheKey the key for the block
* @param buffer the target buffer for the read result
* @param blockOffset offset within the block
* @param off offset within the target buffer
* @param length the number of bytes to read
* @return true if the block was cached and the bytes were read
*/
public boolean fetch(BlockCacheKey blockCacheKey, byte[] buffer,
int blockOffset, int off, int length) {
BlockCacheLocation location = cache.getIfPresent(blockCacheKey);
if (location == null) {
metrics.blockCacheMiss.incrementAndGet();
return false;
}
int bankId = location.getBankId();
int bankOffset = location.getBlock() * blockSize;
location.touch();
ByteBuffer bank = getBank(bankId);
bank.position(bankOffset + blockOffset);
bank.get(buffer, off, length);
if (location.isRemoved()) {
// must check *after* the read is done since the bank may have been reused for another block
// before or during the read.
metrics.blockCacheMiss.incrementAndGet();
return false;
}
metrics.blockCacheHit.incrementAndGet();
return true;
}
public boolean fetch(BlockCacheKey blockCacheKey, byte[] buffer) {
checkLength(buffer);
return fetch(blockCacheKey, buffer, 0, 0, blockSize);
}
private boolean findEmptyLocation(BlockCacheLocation location) {
// This is a tight loop that will try and find a location to
// place the block before giving up
for (int j = 0; j < 10; j++) {
OUTER: for (int bankId = 0; bankId < banks.length; bankId++) {
AtomicInteger bitSetCounter = lockCounters[bankId];
BlockLocks bitSet = locks[bankId];
if (bitSetCounter.get() == numberOfBlocksPerBank) {
// if bitset is full
continue OUTER;
}
// this check needs to spin, if a lock was attempted but not obtained
// the rest of the bank should not be skipped
int bit = bitSet.nextClearBit(0);
INNER: while (bit != -1) {
if (bit >= numberOfBlocksPerBank) {
// bit set is full
continue OUTER;
}
if (!bitSet.set(bit)) {
// lock was not obtained
// this restarts at 0 because another block could have been unlocked
// while this was executing
bit = bitSet.nextClearBit(0);
continue INNER;
} else {
// lock obtained
location.setBankId(bankId);
location.setBlock(bit);
bitSetCounter.incrementAndGet();
return true;
}
}
}
}
return false;
}
private void checkLength(byte[] buffer) {
if (buffer.length != blockSize) {
throw new RuntimeException("Buffer wrong size, expecting [" + blockSize
+ "] got [" + buffer.length + "]");
}
}
/** Returns a new copy of the ByteBuffer for the given bank, so it's safe to call position() on w/o additional synchronization */
private ByteBuffer getBank(int bankId) {
return banks[bankId].duplicate();
}
/** returns the number of elements in the cache */
public int getSize() {
return cache.asMap().size();
}
void setOnRelease(OnRelease onRelease) {
this.onReleases.add(onRelease);
}
}