[Java] Add Java support for cache sharding.

Summary:
Add setCacheNumShardBits() and cacheNumShardBits() to Options.  This allows
developers to control the number of shards for the block cache.

Test Plan:
make rocksdbjava
cd java
make db_bench
./jdb_bench.sh --cache_size=1048576 --cache_numshardbits=6

Reviewers: sdong, ljin, ankgup87

Reviewed By: ankgup87

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19347

java/RocksDBSample.java

@@ -44,6 +44,7 @@ public class RocksDBSample {
         .setBlockSize(64 * SizeUnit.KB)
         .setMaxBackgroundCompactions(10)
         .setFilter(filter)
+        .setCacheNumShardBits(6)
         .setCompressionType(CompressionType.SNAPPY_COMPRESSION);
     Statistics stats = options.statisticsPtr();
 
@@ -53,6 +54,7 @@ public class RocksDBSample {
     assert(options.disableSeekCompaction() == true);
     assert(options.blockSize() == 64 * SizeUnit.KB);
     assert(options.maxBackgroundCompactions() == 10);
+    assert(options.cacheNumShardBits() == 6);
     assert(options.compressionType() == CompressionType.SNAPPY_COMPRESSION);
 
     assert(options.memTableFactoryName().equals("SkipListFactory"));

java/org/rocksdb/Options.java

@@ -14,6 +14,7 @@ package org.rocksdb;
  */
 public class Options extends RocksObject {
   static final long DEFAULT_CACHE_SIZE = 8 << 20;
+  static final int DEFAULT_NUM_SHARD_BITS = -1;
   /**
    * Construct options for opening a RocksDB.
    *
@@ -23,6 +24,7 @@ public class Options extends RocksObject {
   public Options() {
     super();
     cacheSize_ = DEFAULT_CACHE_SIZE;
+    numShardBits_ = DEFAULT_NUM_SHARD_BITS;
     newOptions();
     env_ = RocksEnv.getDefault();
   }
@@ -215,6 +217,7 @@ public class Options extends RocksObject {
    * If cacheSize is non-positive, then cache will not be used.
    *
    * DEFAULT: 8M
+   * @see setCacheNumShardBits()
    */
   public Options setCacheSize(long cacheSize) {
     cacheSize_ = cacheSize;
@@ -223,11 +226,42 @@ public class Options extends RocksObject {
 
   /**
    * @return the amount of cache in bytes that will be used by RocksDB.
+   *
+   * @see cacheNumShardBits()
    */
   public long cacheSize() {
     return cacheSize_;
   }
 
+  /**
+   * Controls the number of shards for the block cache.
+   * This is applied only if cacheSize is set to non-negative.
+   *
+   * @param numShardBits the number of shard bits.  The resulting
+   *     number of shards would be 2 ^ numShardBits.  Any negative
+   *     number means use default settings."
+   * @return the reference to the current option.
+   *
+   * @see setCacheSize()
+   */
+  public Options setCacheNumShardBits(int numShardBits) {
+    numShardBits_ = numShardBits;
+    return this;
+  }
+
+  /**
+   * Returns the number of shard bits used in the block cache.
+   * The resulting number of shards would be 2 ^ (returned value).
+   * Any negative number means use default settings.
+   *
+   * @return the number of shard bits used in the block cache.
+   *
+   * @see cacheSize()
+   */
+  public int cacheNumShardBits() {
+    return numShardBits_;
+  }
+
   /**
    * If true, an error will be thrown during RocksDB.open() if the
    * database already exists.
@@ -2397,6 +2431,7 @@ public class Options extends RocksObject {
       long handle, int prefixLength);
 
   long cacheSize_;
+  int numShardBits_;
   Filter filter_;
   RocksEnv env_;
 }

java/org/rocksdb/RocksDB.java

@@ -106,7 +106,8 @@ public class RocksDB extends RocksObject {
     // in RocksDB can prevent Java to GC during the life-time of
     // the currently-created RocksDB.
     RocksDB db = new RocksDB();
-    db.open(options.nativeHandle_, options.cacheSize_, path);
+    db.open(options.nativeHandle_, options.cacheSize_,
+            options.numShardBits_, path);
     db.transferCppRawPointersOwnershipFrom(options);
     return db;
   }
@@ -330,7 +331,8 @@ public class RocksDB extends RocksObject {
 
   // native methods
   protected native void open(
-      long optionsHandle, long cacheSize, String path) throws RocksDBException;
+      long optionsHandle, long cacheSize, int numShardBits,
+      String path) throws RocksDBException;
   protected native void put(
       long handle, byte[] key, int keyLen,
       byte[] value, int valueLen) throws RocksDBException;

java/org/rocksdb/benchmark/DbBenchmark.java

@@ -534,6 +534,8 @@ public class DbBenchmark {
         (Integer)flags_.get(Flag.max_background_flushes));
     options.setCacheSize(
         (Long)flags_.get(Flag.cache_size));
+    options.setCacheNumShardBits(
+        (Integer)flags_.get(Flag.cache_numshardbits));
     options.setBlockSize(
         (Long)flags_.get(Flag.block_size));
     options.setMaxOpenFiles(
@@ -616,7 +618,6 @@ public class DbBenchmark {
     options.setCompressionLevel((Integer)flags_.get(Flag.compression_level));
     options.setMinLevelToCompress((Integer)flags_.get(Flag.min_level_to_compress));
     options.setHdfs((String)flags_.get(Flag.hdfs)); // env
-    options.setCacheNumshardbits((Integer)flags_.get(Flag.cache_numshardbits));
     options.setStatistics((Boolean)flags_.get(Flag.statistics));
     options.setUniversalSizeRatio(
         (Integer)flags_.get(Flag.universal_size_ratio));

java/rocksjni/rocksjni.cc

@@ -27,11 +27,15 @@
  */
 void Java_org_rocksdb_RocksDB_open(
     JNIEnv* env, jobject jdb, jlong jopt_handle,
-    jlong jcache_size, jstring jdb_path) {
+    jlong jcache_size, jint jnum_shardbits, jstring jdb_path) {
   auto opt = reinterpret_cast<rocksdb::Options*>(jopt_handle);
   if (jcache_size > 0) {
     opt->no_block_cache = false;
+    if (jnum_shardbits >= 1) {
+      opt->block_cache = rocksdb::NewLRUCache(jcache_size, jnum_shardbits);
+    } else {
       opt->block_cache = rocksdb::NewLRUCache(jcache_size);
+    }
   } else {
     opt->no_block_cache = true;
     opt->block_cache = nullptr;