presto-main/src/main/java/io/prestosql/operator/OperationTimer.java/OperationTimer/toString
class OperationTimer:        @Override
        public String toString()
        {
            return toStringHelper(this)
                    .add("calls", calls)
                    .add("wallNanos", wallNanos)
                    .add("cpuNanos", cpuNanos)
                    .toString();
        }