It should be Debug level.
https://github.com/alibaba/dubbo/blob/23084275bf695f41b5f84d927c351e9b2b04a2be/dubbo-monitor/dubbo-monitor-default/src/main/java/com/alibaba/dubbo/monitor/dubbo/DubboMonitor.java#L77
* 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 com.alibaba.dubbo.monitor.dubbo;
import com.alibaba.dubbo.common.Constants;
import com.alibaba.dubbo.common.URL;
import com.alibaba.dubbo.common.logger.Logger;
import com.alibaba.dubbo.common.logger.LoggerFactory;
import com.alibaba.dubbo.common.utils.NamedThreadFactory;
import com.alibaba.dubbo.monitor.Monitor;
import com.alibaba.dubbo.monitor.MonitorService;
import com.alibaba.dubbo.rpc.Invoker;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
/**
 * DubboMonitor
 */
public class DubboMonitor implements Monitor {
    private static final Logger logger = LoggerFactory.getLogger(DubboMonitor.class);
    private static final int LENGTH = 10;
    private final ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(3, new NamedThreadFactory("DubboMonitorSendTimer", true));
    private final ScheduledFuture<?> sendFuture;