GH-5343 Implement sizeInternal method to improve size calculation in LmdbStoreConnection

Author: odysa

core/sail/lmdb/src/main/java/org/eclipse/rdf4j/sail/lmdb/LmdbStoreConnection.java

@@ -27,6 +27,8 @@
 import org.eclipse.rdf4j.sail.helpers.DefaultSailChangedEvent;
 import org.eclipse.rdf4j.sail.lmdb.model.LmdbValue;
 
+import java.util.stream.Stream;
+
 /**
  * Connection to an {@link LmdbStore}.
  */
@@ -163,6 +165,14 @@ public Statement next() throws SailException {
 		};
 	}
 
+	@Override
+	protected long sizeInternal(Resource... contexts) throws SailException {
+		try (Stream<? extends Statement> stream = super.getStatementsInternal(null, null, null, false, contexts)
+				.stream()) {
+			return stream.count();
+		}
+	}
+
 	/**
 	 * Ensures that all components of the value are initialized from the underlying database.
 	 *