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/**
* 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;
import static org.apache.hadoop.hbase.HConstants.BUCKET_CACHE_IOENGINE_KEY;
import static org.apache.hadoop.hbase.HConstants.BUCKET_CACHE_SIZE_KEY;
import java.io.IOException;
import java.lang.management.ManagementFactory;
import java.lang.management.MemoryUsage;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.HColumnDescriptor;
import org.apache.hadoop.hbase.HConstants;
import org.apache.hadoop.hbase.io.hfile.BlockType.BlockCategory;
import org.apache.hadoop.hbase.io.hfile.bucket.BucketCache;
import org.apache.hadoop.hbase.util.ReflectionUtils;
import org.apache.hadoop.util.StringUtils;
import com.google.common.annotations.VisibleForTesting;
/**
* Stores all of the cache objects and configuration for a single HFile.
*/
@InterfaceAudience.Private
public class CacheConfig {
private static final Log LOG = LogFactory.getLog(CacheConfig.class.getName());
/**
* Configuration key to cache data blocks on write. There are separate
* switches for bloom blocks and non-root index blocks.
*/
public static final String CACHE_BLOCKS_ON_WRITE_KEY =
"hbase.rs.cacheblocksonwrite";
/**
* Configuration key to cache leaf and intermediate-level index blocks on
* write.
*/
public static final String CACHE_INDEX_BLOCKS_ON_WRITE_KEY =
"hfile.block.index.cacheonwrite";
/**
* Configuration key to cache compound bloom filter blocks on write.
*/
public static final String CACHE_BLOOM_BLOCKS_ON_WRITE_KEY =
"hfile.block.bloom.cacheonwrite";
/**
* Configuration key to cache data blocks in compressed and/or encrypted format.
*/
public static final String CACHE_DATA_BLOCKS_COMPRESSED_KEY =
"hbase.block.data.cachecompressed";
/**
* Configuration key to evict all blocks of a given file from the block cache
* when the file is closed.
*/
public static final String EVICT_BLOCKS_ON_CLOSE_KEY =
"hbase.rs.evictblocksonclose";
/**
* Configuration keys for Bucket cache
*/
/**
* If the chosen ioengine can persist its state across restarts, the path to the file to
* persist to.
*/
public static final String BUCKET_CACHE_PERSISTENT_PATH_KEY =
"hbase.bucketcache.persistent.path";
/**
* If the bucket cache is used in league with the lru on-heap block cache (meta blocks such
* as indices and blooms are kept in the lru blockcache and the data blocks in the
* bucket cache).
*/
public static final String BUCKET_CACHE_COMBINED_KEY =
"hbase.bucketcache.combinedcache.enabled";
public static final String BUCKET_CACHE_WRITER_THREADS_KEY = "hbase.bucketcache.writer.threads";
public static final String BUCKET_CACHE_WRITER_QUEUE_KEY =
"hbase.bucketcache.writer.queuelength";
/**
* A comma-delimited array of values for use as bucket sizes.
*/
public static final String BUCKET_CACHE_BUCKETS_KEY = "hbase.bucketcache.bucket.sizes";
/**
* Defaults for Bucket cache
*/
public static final boolean DEFAULT_BUCKET_CACHE_COMBINED = true;
public static final int DEFAULT_BUCKET_CACHE_WRITER_THREADS = 3;
public static final int DEFAULT_BUCKET_CACHE_WRITER_QUEUE = 64;
/**
* Configuration key to prefetch all blocks of a given file into the block cache
* when the file is opened.
*/
public static final String PREFETCH_BLOCKS_ON_OPEN_KEY =
"hbase.rs.prefetchblocksonopen";
/**
* The target block size used by blockcache instances. Defaults to
* {@link HConstants#DEFAULT_BLOCKSIZE}.
* TODO: this config point is completely wrong, as it's used to determine the
* target block size of BlockCache instances. Rename.
*/
public static final String BLOCKCACHE_BLOCKSIZE_KEY = "hbase.offheapcache.minblocksize";
private static final String EXTERNAL_BLOCKCACHE_KEY = "hbase.blockcache.use.external";
private static final boolean EXTERNAL_BLOCKCACHE_DEFAULT = false;
private static final String EXTERNAL_BLOCKCACHE_CLASS_KEY="hbase.blockcache.external.class";
/**
* Enum of all built in external block caches.
* This is used for config.
*/
private static enum ExternalBlockCaches {
memcached(MemcachedBlockCache.class);
// TODO(eclark): Consider more. Redis, etc.
Class clazz;
ExternalBlockCaches(Class clazz) {
this.clazz = clazz;
}
}
// Defaults
public static final boolean DEFAULT_CACHE_DATA_ON_READ = true;
public static final boolean DEFAULT_CACHE_DATA_ON_WRITE = false;
public static final boolean DEFAULT_IN_MEMORY = false;
public static final boolean DEFAULT_CACHE_INDEXES_ON_WRITE = false;
public static final boolean DEFAULT_CACHE_BLOOMS_ON_WRITE = false;
public static final boolean DEFAULT_EVICT_ON_CLOSE = false;
public static final boolean DEFAULT_CACHE_DATA_COMPRESSED = false;
public static final boolean DEFAULT_PREFETCH_ON_OPEN = false;
/** Local reference to the block cache, null if completely disabled */
private final BlockCache blockCache;
/**
* Whether blocks should be cached on read (default is on if there is a
* cache but this can be turned off on a per-family or per-request basis).
* If off we will STILL cache meta blocks; i.e. INDEX and BLOOM types.
* This cannot be disabled.
*/
private boolean cacheDataOnRead;
/** Whether blocks should be flagged as in-memory when being cached */
private final boolean inMemory;
/** Whether data blocks should be cached when new files are written */
private boolean cacheDataOnWrite;
/** Whether index blocks should be cached when new files are written */
private final boolean cacheIndexesOnWrite;
/** Whether compound bloom filter blocks should be cached on write */
private final boolean cacheBloomsOnWrite;
/** Whether blocks of a file should be evicted when the file is closed */
private boolean evictOnClose;
/** Whether data blocks should be stored in compressed and/or encrypted form in the cache */
private final boolean cacheDataCompressed;
/** Whether data blocks should be prefetched into the cache */
private final boolean prefetchOnOpen;
/**
* If true and if more than one tier in this cache deploy -- e.g. CombinedBlockCache has an L1
* and an L2 tier -- then cache data blocks up in the L1 tier (The meta blocks are likely being
* cached up in L1 already. At least this is the case if CombinedBlockCache).
*/
private boolean cacheDataInL1;
/**
* Create a cache configuration using the specified configuration object and
* family descriptor.
* @param conf hbase configuration
* @param family column family configuration
*/
public CacheConfig(Configuration conf, HColumnDescriptor family) {
this(CacheConfig.instantiateBlockCache(conf),
family.isBlockCacheEnabled(),
family.isInMemory(),
// For the following flags we enable them regardless of per-schema settings
// if they are enabled in the global configuration.
conf.getBoolean(CACHE_BLOCKS_ON_WRITE_KEY,
DEFAULT_CACHE_DATA_ON_WRITE) || family.isCacheDataOnWrite(),
conf.getBoolean(CACHE_INDEX_BLOCKS_ON_WRITE_KEY,
DEFAULT_CACHE_INDEXES_ON_WRITE) || family.isCacheIndexesOnWrite(),
conf.getBoolean(CACHE_BLOOM_BLOCKS_ON_WRITE_KEY,
DEFAULT_CACHE_BLOOMS_ON_WRITE) || family.isCacheBloomsOnWrite(),
conf.getBoolean(EVICT_BLOCKS_ON_CLOSE_KEY,
DEFAULT_EVICT_ON_CLOSE) || family.isEvictBlocksOnClose(),
conf.getBoolean(CACHE_DATA_BLOCKS_COMPRESSED_KEY, DEFAULT_CACHE_DATA_COMPRESSED),
conf.getBoolean(PREFETCH_BLOCKS_ON_OPEN_KEY,
DEFAULT_PREFETCH_ON_OPEN) || family.isPrefetchBlocksOnOpen(),
conf.getBoolean(HColumnDescriptor.CACHE_DATA_IN_L1,
HColumnDescriptor.DEFAULT_CACHE_DATA_IN_L1) || family.isCacheDataInL1()
);
}
/**
* Create a cache configuration using the specified configuration object and
* defaults for family level settings.
* @param conf hbase configuration
*/
public CacheConfig(Configuration conf) {
this(CacheConfig.instantiateBlockCache(conf),
DEFAULT_CACHE_DATA_ON_READ,
DEFAULT_IN_MEMORY, // This is a family-level setting so can't be set
// strictly from conf
conf.getBoolean(CACHE_BLOCKS_ON_WRITE_KEY, DEFAULT_CACHE_DATA_ON_WRITE),
conf.getBoolean(CACHE_INDEX_BLOCKS_ON_WRITE_KEY, DEFAULT_CACHE_INDEXES_ON_WRITE),
conf.getBoolean(CACHE_BLOOM_BLOCKS_ON_WRITE_KEY, DEFAULT_CACHE_BLOOMS_ON_WRITE),
conf.getBoolean(EVICT_BLOCKS_ON_CLOSE_KEY, DEFAULT_EVICT_ON_CLOSE),
conf.getBoolean(CACHE_DATA_BLOCKS_COMPRESSED_KEY, DEFAULT_CACHE_DATA_COMPRESSED),
conf.getBoolean(PREFETCH_BLOCKS_ON_OPEN_KEY, DEFAULT_PREFETCH_ON_OPEN),
conf.getBoolean(HColumnDescriptor.CACHE_DATA_IN_L1,
HColumnDescriptor.DEFAULT_CACHE_DATA_IN_L1)
);
}
/**
* Create a block cache configuration with the specified cache and
* configuration parameters.
* @param blockCache reference to block cache, null if completely disabled
* @param cacheDataOnRead whether DATA blocks should be cached on read (we always cache INDEX
* blocks and BLOOM blocks; this cannot be disabled).
* @param inMemory whether blocks should be flagged as in-memory
* @param cacheDataOnWrite whether data blocks should be cached on write
* @param cacheIndexesOnWrite whether index blocks should be cached on write
* @param cacheBloomsOnWrite whether blooms should be cached on write
* @param evictOnClose whether blocks should be evicted when HFile is closed
* @param cacheDataCompressed whether to store blocks as compressed in the cache
* @param prefetchOnOpen whether to prefetch blocks upon open
* @param cacheDataInL1 If more than one cache tier deployed, if true, cache this column families
* data blocks up in the L1 tier.
*/
CacheConfig(final BlockCache blockCache,
final boolean cacheDataOnRead, final boolean inMemory,
final boolean cacheDataOnWrite, final boolean cacheIndexesOnWrite,
final boolean cacheBloomsOnWrite, final boolean evictOnClose,
final boolean cacheDataCompressed, final boolean prefetchOnOpen,
final boolean cacheDataInL1) {
this.blockCache = blockCache;
this.cacheDataOnRead = cacheDataOnRead;
this.inMemory = inMemory;
this.cacheDataOnWrite = cacheDataOnWrite;
this.cacheIndexesOnWrite = cacheIndexesOnWrite;
this.cacheBloomsOnWrite = cacheBloomsOnWrite;
this.evictOnClose = evictOnClose;
this.cacheDataCompressed = cacheDataCompressed;
this.prefetchOnOpen = prefetchOnOpen;
this.cacheDataInL1 = cacheDataInL1;
LOG.info(this);
}
/**
* Constructs a cache configuration copied from the specified configuration.
* @param cacheConf
*/
public CacheConfig(CacheConfig cacheConf) {
this(cacheConf.blockCache, cacheConf.cacheDataOnRead, cacheConf.inMemory,
cacheConf.cacheDataOnWrite, cacheConf.cacheIndexesOnWrite,
cacheConf.cacheBloomsOnWrite, cacheConf.evictOnClose,
cacheConf.cacheDataCompressed, cacheConf.prefetchOnOpen,
cacheConf.cacheDataInL1);
}
/**
* Checks whether the block cache is enabled.
*/
public boolean isBlockCacheEnabled() {
return this.blockCache != null;
}
/**
* Returns the block cache.
* @return the block cache, or null if caching is completely disabled
*/
public BlockCache getBlockCache() {
return this.blockCache;
}
/**
* Returns whether the DATA blocks of this HFile should be cached on read or not (we always
* cache the meta blocks, the INDEX and BLOOM blocks).
* @return true if blocks should be cached on read, false if not
*/
public boolean shouldCacheDataOnRead() {
return isBlockCacheEnabled() && cacheDataOnRead;
}
/**
* Should we cache a block of a particular category? We always cache
* important blocks such as index blocks, as long as the block cache is
* available.
*/
public boolean shouldCacheBlockOnRead(BlockCategory category) {
return isBlockCacheEnabled()
&& (cacheDataOnRead ||
category == BlockCategory.INDEX ||
category == BlockCategory.BLOOM ||
(prefetchOnOpen &&
(category != BlockCategory.META &&
category != BlockCategory.UNKNOWN)));
}
/**
* @return true if blocks in this file should be flagged as in-memory
*/
public boolean isInMemory() {
return isBlockCacheEnabled() && this.inMemory;
}
/**
* @return True if cache data blocks in L1 tier (if more than one tier in block cache deploy).
*/
public boolean isCacheDataInL1() {
return isBlockCacheEnabled() && this.cacheDataInL1;
}
/**
* @return true if data blocks should be written to the cache when an HFile is
* written, false if not
*/
public boolean shouldCacheDataOnWrite() {
return isBlockCacheEnabled() && this.cacheDataOnWrite;
}
/**
* Only used for testing.
* @param cacheDataOnWrite whether data blocks should be written to the cache
* when an HFile is written
*/
@VisibleForTesting
public void setCacheDataOnWrite(boolean cacheDataOnWrite) {
this.cacheDataOnWrite = cacheDataOnWrite;
}
/**
* Only used for testing.
* @param cacheDataInL1 Whether to cache data blocks up in l1 (if a multi-tier cache
* implementation).
*/
@VisibleForTesting
public void setCacheDataInL1(boolean cacheDataInL1) {
this.cacheDataInL1 = cacheDataInL1;
}
/**
* @return true if index blocks should be written to the cache when an HFile
* is written, false if not
*/
public boolean shouldCacheIndexesOnWrite() {
return isBlockCacheEnabled() && this.cacheIndexesOnWrite;
}
/**
* @return true if bloom blocks should be written to the cache when an HFile
* is written, false if not
*/
public boolean shouldCacheBloomsOnWrite() {
return isBlockCacheEnabled() && this.cacheBloomsOnWrite;
}
/**
* @return true if blocks should be evicted from the cache when an HFile
* reader is closed, false if not
*/
public boolean shouldEvictOnClose() {
return isBlockCacheEnabled() && this.evictOnClose;
}
/**
* Only used for testing.
* @param evictOnClose whether blocks should be evicted from the cache when an
* HFile reader is closed
*/
public void setEvictOnClose(boolean evictOnClose) {
this.evictOnClose = evictOnClose;
}
/**
* @return true if data blocks should be compressed in the cache, false if not
*/
public boolean shouldCacheDataCompressed() {
return isBlockCacheEnabled() && this.cacheDataCompressed;
}
/**
* @return true if this {@link BlockCategory} should be compressed in blockcache, false otherwise
*/
public boolean shouldCacheCompressed(BlockCategory category) {
if (!isBlockCacheEnabled()) return false;
switch (category) {
case DATA:
return this.cacheDataCompressed;
default:
return false;
}
}
/**
* @return true if blocks should be prefetched into the cache on open, false if not
*/
public boolean shouldPrefetchOnOpen() {
return isBlockCacheEnabled() && this.prefetchOnOpen;
}
/**
* Return true if we may find this type of block in block cache.
*
* TODO: today {@code family.isBlockCacheEnabled()} only means {@code cacheDataOnRead}, so here we
* consider lots of other configurations such as {@code cacheDataOnWrite}. We should fix this in
* the future, {@code cacheDataOnWrite} should honor the CF level {@code isBlockCacheEnabled}
* configuration.
*/
public boolean shouldReadBlockFromCache(BlockType blockType) {
if (!isBlockCacheEnabled()) {
return false;
}
if (cacheDataOnRead) {
return true;
}
if (prefetchOnOpen) {
return true;
}
if (cacheDataOnWrite) {
return true;
}
if (blockType == null) {
return true;
}
if (blockType.getCategory() == BlockCategory.BLOOM ||
blockType.getCategory() == BlockCategory.INDEX) {
return true;
}
return false;
}
/**
* If we make sure the block could not be cached, we will not acquire the lock
* otherwise we will acquire lock
*/
public boolean shouldLockOnCacheMiss(BlockType blockType) {
if (blockType == null) {
return true;
}
return shouldCacheBlockOnRead(blockType.getCategory());
}
@Override
public String toString() {
if (!isBlockCacheEnabled()) {
return "CacheConfig:disabled";
}
return "blockCache=" + getBlockCache() +
", cacheDataOnRead=" + shouldCacheDataOnRead() +
", cacheDataOnWrite=" + shouldCacheDataOnWrite() +
", cacheIndexesOnWrite=" + shouldCacheIndexesOnWrite() +
", cacheBloomsOnWrite=" + shouldCacheBloomsOnWrite() +
", cacheEvictOnClose=" + shouldEvictOnClose() +
", cacheDataCompressed=" + shouldCacheDataCompressed() +
", prefetchOnOpen=" + shouldPrefetchOnOpen();
}
// Static block cache reference and methods
/**
* Static reference to the block cache, or null if no caching should be used
* at all.
*/
// Clear this if in tests you'd make more than one block cache instance.
@VisibleForTesting
static BlockCache GLOBAL_BLOCK_CACHE_INSTANCE;
/** Boolean whether we have disabled the block cache entirely. */
@VisibleForTesting
static boolean blockCacheDisabled = false;
static long getLruCacheSize(final Configuration conf, final MemoryUsage mu) {
float cachePercentage = conf.getFloat(HConstants.HFILE_BLOCK_CACHE_SIZE_KEY,
HConstants.HFILE_BLOCK_CACHE_SIZE_DEFAULT);
if (cachePercentage <= 0.0001f) {
blockCacheDisabled = true;
return -1;
}
if (cachePercentage > 1.0) {
throw new IllegalArgumentException(HConstants.HFILE_BLOCK_CACHE_SIZE_KEY +
" must be between 0.0 and 1.0, and not > 1.0");
}
// Calculate the amount of heap to give the heap.
return (long) (mu.getMax() * cachePercentage);
}
/**
* @param c Configuration to use.
* @param mu JMX Memory Bean
* @return An L1 instance. Currently an instance of LruBlockCache.
*/
private static LruBlockCache getL1(final Configuration c, final MemoryUsage mu) {
long lruCacheSize = getLruCacheSize(c, mu);
if (lruCacheSize < 0) return null;
int blockSize = c.getInt(BLOCKCACHE_BLOCKSIZE_KEY, HConstants.DEFAULT_BLOCKSIZE);
LOG.info("Allocating LruBlockCache size=" +
StringUtils.byteDesc(lruCacheSize) + ", blockSize=" + StringUtils.byteDesc(blockSize));
return new LruBlockCache(lruCacheSize, blockSize, true, c);
}
/**
* @param c Configuration to use.
* @param mu JMX Memory Bean
* @return Returns L2 block cache instance (for now it is BucketCache BlockCache all the time)
* or null if not supposed to be a L2.
*/
private static BlockCache getL2(final Configuration c, final MemoryUsage mu) {
final boolean useExternal = c.getBoolean(EXTERNAL_BLOCKCACHE_KEY, EXTERNAL_BLOCKCACHE_DEFAULT);
if (LOG.isDebugEnabled()) {
LOG.debug("Trying to use " + (useExternal?" External":" Internal") + " l2 cache");
}
// If we want to use an external block cache then create that.
if (useExternal) {
return getExternalBlockcache(c);
}
// otherwise use the bucket cache.
return getBucketCache(c, mu);
}
private static BlockCache getExternalBlockcache(Configuration c) {
Class klass = null;
// Get the class, from the config. s
try {
klass = ExternalBlockCaches.valueOf(c.get(EXTERNAL_BLOCKCACHE_CLASS_KEY, "memcache")).clazz;
} catch (IllegalArgumentException exception) {
klass = c.getClass(EXTERNAL_BLOCKCACHE_CLASS_KEY, MemcachedBlockCache.class);
}
// Now try and create an instance of the block cache.
try {
LOG.info("Creating external block cache of type: " + klass);
return (BlockCache) ReflectionUtils.newInstance(klass, c);
} catch (Exception e) {
LOG.warn("Error creating external block cache", e);
}
return null;
}
private static BlockCache getBucketCache(Configuration c, MemoryUsage mu) {
// Check for L2. ioengine name must be non-null.
String bucketCacheIOEngineName = c.get(BUCKET_CACHE_IOENGINE_KEY, null);
if (bucketCacheIOEngineName == null || bucketCacheIOEngineName.length() <= 0) return null;
int blockSize = c.getInt(BLOCKCACHE_BLOCKSIZE_KEY, HConstants.DEFAULT_BLOCKSIZE);
float bucketCachePercentage = c.getFloat(BUCKET_CACHE_SIZE_KEY, 0F);
long bucketCacheSize = (long) (bucketCachePercentage < 1? mu.getMax() * bucketCachePercentage:
bucketCachePercentage * 1024 * 1024);
if (bucketCacheSize <= 0) {
throw new IllegalStateException("bucketCacheSize <= 0; Check " +
BUCKET_CACHE_SIZE_KEY + " setting and/or server java heap size");
}
if (c.get("hbase.bucketcache.percentage.in.combinedcache") != null) {
LOG.warn("Configuration 'hbase.bucketcache.percentage.in.combinedcache' is no longer "
+ "respected. See comments in http://hbase.apache.org/book.html#_changes_of_note");
}
int writerThreads = c.getInt(BUCKET_CACHE_WRITER_THREADS_KEY,
DEFAULT_BUCKET_CACHE_WRITER_THREADS);
int writerQueueLen = c.getInt(BUCKET_CACHE_WRITER_QUEUE_KEY,
DEFAULT_BUCKET_CACHE_WRITER_QUEUE);
String persistentPath = c.get(BUCKET_CACHE_PERSISTENT_PATH_KEY);
String[] configuredBucketSizes = c.getStrings(BUCKET_CACHE_BUCKETS_KEY);
int [] bucketSizes = null;
if (configuredBucketSizes != null) {
bucketSizes = new int[configuredBucketSizes.length];
for (int i = 0; i < configuredBucketSizes.length; i++) {
bucketSizes[i] = Integer.parseInt(configuredBucketSizes[i].trim());
}
}
BucketCache bucketCache = null;
try {
int ioErrorsTolerationDuration = c.getInt(
"hbase.bucketcache.ioengine.errors.tolerated.duration",
BucketCache.DEFAULT_ERROR_TOLERATION_DURATION);
// Bucket cache logs its stats on creation internal to the constructor.
bucketCache = new BucketCache(bucketCacheIOEngineName,
bucketCacheSize, blockSize, bucketSizes, writerThreads, writerQueueLen, persistentPath,
ioErrorsTolerationDuration);
} catch (IOException ioex) {
LOG.error("Can't instantiate bucket cache", ioex); throw new RuntimeException(ioex);
}
return bucketCache;
}
/**
* Returns the block cache or null in case none should be used.
* Sets GLOBAL_BLOCK_CACHE_INSTANCE
*
* @param conf The current configuration.
* @return The block cache or null.
*/
public static synchronized BlockCache instantiateBlockCache(Configuration conf) {
if (GLOBAL_BLOCK_CACHE_INSTANCE != null) return GLOBAL_BLOCK_CACHE_INSTANCE;
if (blockCacheDisabled) return null;
MemoryUsage mu = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage();
LruBlockCache l1 = getL1(conf, mu);
// blockCacheDisabled is set as a side-effect of getL1(), so check it again after the call.
if (blockCacheDisabled) return null;
BlockCache l2 = getL2(conf, mu);
if (l2 == null) {
GLOBAL_BLOCK_CACHE_INSTANCE = l1;
} else {
boolean useExternal = conf.getBoolean(EXTERNAL_BLOCKCACHE_KEY, EXTERNAL_BLOCKCACHE_DEFAULT);
boolean combinedWithLru = conf.getBoolean(BUCKET_CACHE_COMBINED_KEY,
DEFAULT_BUCKET_CACHE_COMBINED);
if (useExternal) {
GLOBAL_BLOCK_CACHE_INSTANCE = new InclusiveCombinedBlockCache(l1, l2);
} else {
if (combinedWithLru) {
GLOBAL_BLOCK_CACHE_INSTANCE = new CombinedBlockCache(l1, l2);
} else {
// L1 and L2 are not 'combined'. They are connected via the LruBlockCache victimhandler
// mechanism. It is a little ugly but works according to the following: when the
// background eviction thread runs, blocks evicted from L1 will go to L2 AND when we get
// a block from the L1 cache, if not in L1, we will search L2.
GLOBAL_BLOCK_CACHE_INSTANCE = l1;
}
}
l1.setVictimCache(l2);
}
return GLOBAL_BLOCK_CACHE_INSTANCE;
}
}