add GetAggregatedLongProperty for Java API (#4379)

Summary:
Add Java API `getAggregatedLongProperty(final String property)`
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4379

Differential Revision: D9921463

Pulled By: sagar0

fbshipit-source-id: a02512e1b2aff4765a10b77de9a7bf7b1909d954

java/rocksjni/rocksjni.cc

@@ -1844,6 +1844,32 @@ jlong Java_org_rocksdb_RocksDB_getLongProperty__JJLjava_lang_String_2I(
   return 0;
 }
 
+/*
+ * Class:     org_rocksdb_RocksDB
+ * Method:    getAggregatedLongProperty
+ * Signature: (JLjava/lang/String;I)J
+ */
+jlong Java_org_rocksdb_RocksDB_getAggregatedLongProperty(
+    JNIEnv* env, jobject, jlong db_handle, jstring jproperty, jint jproperty_len) {
+  const char* property = env->GetStringUTFChars(jproperty, nullptr);
+  if (property == nullptr) {
+    return 0;
+  }
+  rocksdb::Slice property_slice(property, jproperty_len);
+  auto* db = reinterpret_cast<rocksdb::DB*>(db_handle);
+  uint64_t property_value = 0;
+  bool retCode = db->GetAggregatedIntProperty(property_slice, &property_value);
+  env->ReleaseStringUTFChars(jproperty, property);
+
+  if (retCode) {
+    return property_value;
+  }
+
+  rocksdb::RocksDBExceptionJni::ThrowNew(env, rocksdb::Status::NotFound());
+  return 0;
+}
+
+
 //////////////////////////////////////////////////////////////////////////////
 // rocksdb::DB::Flush
 

java/src/main/java/org/rocksdb/RocksDB.java

@@ -1518,6 +1518,31 @@ public class RocksDB extends RocksObject {
         property, property.length());
   }
 
+ /**
+   * <p> Return sum of the getLongProperty of all the column families</p>
+   *
+   * <p><strong>Note</strong>: As the returned property is of type
+   * {@code uint64_t} on C++ side the returning value can be negative
+   * because Java supports in Java 7 only signed long values.</p>
+   *
+   * <p><strong>Java 7</strong>: To mitigate the problem of the non
+   * existent unsigned long tpye, values should be encapsulated using
+   * {@link java.math.BigInteger} to reflect the correct value. The correct
+   * behavior is guaranteed if {@code 2^64} is added to negative values.</p>
+   *
+   * <p><strong>Java 8</strong>: In Java 8 the value should be treated as
+   * unsigned long using provided methods of type {@link Long}.</p>
+   *
+   * @param property to be fetched.
+   *
+   * @return numerical property value
+   *
+   * @throws RocksDBException if an error happens in the underlying native code.
+   */
+  public long getAggregatedLongProperty(final String property) throws RocksDBException {
+    return getAggregatedLongProperty(nativeHandle_, property, property.length());
+  }
+
   /**
    * <p>Return a heap-allocated iterator over the contents of the
    * database. The result of newIterator() is initially invalid
@@ -2383,6 +2408,8 @@ public class RocksDB extends RocksObject {
       int propertyLength) throws RocksDBException;
   protected native long getLongProperty(long nativeHandle, long cfHandle,
       String property, int propertyLength) throws RocksDBException;
+  protected native long getAggregatedLongProperty(long nativeHandle, String property,
+      int propertyLength) throws RocksDBException;
   protected native long iterator(long handle);
   protected native long iterator(long handle, long readOptHandle);
   protected native long iteratorCF(long handle, long cfHandle);

java/src/test/java/org/rocksdb/ColumnFamilyTest.java

@@ -404,6 +404,10 @@ public class ColumnFamilyTest {
             "rocksdb.stats")).isNotNull();
         assertThat(db.getProperty(columnFamilyHandleList.get(1),
             "rocksdb.sstables")).isNotNull();
+        assertThat(db.getAggregatedLongProperty("rocksdb.estimate-num-keys")).
+            isNotNull();
+        assertThat(db.getAggregatedLongProperty("rocksdb.estimate-num-keys")).
+            isGreaterThanOrEqualTo(0);
       } finally {
         for (final ColumnFamilyHandle columnFamilyHandle :
             columnFamilyHandleList) {