Function assign_event_time_watermarks 

pub fn assign_event_time_watermarks<T, Mat>(
    source: Source<T, Mat>,
    schema: &Schema,
    config: EventTimeConfig,
) -> Result<Source<SqlEvent<T>, Mat>>
where
    T: SqlEventPayload + Send + 'static,
    Mat: Send + 'static,

Assigns event-time watermarks to a source.

The returned source emits each data payload followed by a watermark whenever the configured bounded-out-of-orderness strategy advances.