Add bloom filters

Author: Ankit Gupta

java/RocksDBSample.java

@@ -38,7 +38,8 @@ public static void main(String[] args) {
         .setMaxWriteBufferNumber(3)
         .setDisableSeekCompaction(true)
         .setBlockSize(64 * SizeUnit.KB)
-        .setMaxBackgroundCompactions(10);
+        .setMaxBackgroundCompactions(10)
+        .createBloomFilter(10);
     Statistics stats = options.statisticsPtr();
 
     assert(options.createIfMissing() == true);

java/org/rocksdb/Options.java

@@ -143,6 +143,28 @@ public long blockSize() {
     assert(isInitialized());
     return blockSize(nativeHandle_);
   }
+  
+  /**
+   * Filters are stored in rocksdb and are consulted automatically
+   * by rocksdb to decide whether or not to read some
+   * information from disk. In many cases, a filter can cut down the
+   * number of disk seeks form a handful to a single disk seek per
+   * DB::Get() call.
+   * 
+   * This function a new filter policy that uses a bloom filter 
+   * with approximately the specified number of bits per key.  
+   * A good value for bitsPerKey is 10, which yields a filter 
+   * with ~ 1% false positive rate.
+   * 
+   * @param Bits per key for bloom filter.
+   * @return the instance of the current Options.
+   * @see RocksDB.open()
+   */
+  public Options createBloomFilter(int bitsPerKey) {
+    assert(isInitialized());
+    createBloomFilter0(nativeHandle_, bitsPerKey);
+    return this;
+  }
 
   /*
    * Disable compaction triggered by seek.
@@ -1237,6 +1259,8 @@ private native void setMaxBackgroundCompactions(
 
   private native void useFixedLengthPrefixExtractor(
       long handle, int prefixLength);
+  
+  private native void createBloomFilter0(long handle, int bitsPerKey);
 
   long nativeHandle_;
   long cacheSize_;

java/rocksjni/options.cc

@@ -21,6 +21,7 @@
 #include "rocksdb/memtablerep.h"
 #include "rocksdb/table.h"
 #include "rocksdb/slice_transform.h"
+#include "rocksdb/filter_policy.h"
 
 /*
  * Class:     org_rocksdb_Options
@@ -119,6 +120,23 @@ jlong Java_org_rocksdb_Options_statisticsPtr(
   return reinterpret_cast<jlong>(st);
 }
 
+/*
+ * Class:     org_rocksdb_Options
+ * Method:    createBloomFilter0
+ * Signature: (JI)V
+ */
+void Java_org_rocksdb_Options_createBloomFilter0(
+    JNIEnv* env, jobject jobj, jlong jhandle, jint jbits_per_key) {
+  rocksdb::Options* opt = reinterpret_cast<rocksdb::Options*>(jhandle);
+  
+  // Delete previously allocated pointer
+  if(opt->filter_policy) {
+    delete opt->filter_policy;
+  }
+  
+  opt->filter_policy = rocksdb::NewBloomFilterPolicy(jbits_per_key);
+}
+
 /*
  * Class:     org_rocksdb_Options
  * Method:    maxWriteBufferNumber