/// Returns the last observed watermark value, if available.
///
/// The [`Instant`] in the returned tuple is the approximate instant the
/// watermark was observed, allowing the caller to determine the staleness
/// of the value.
///
/// If the watermark value has yet to be observed (i.e. due to continuous
/// fetch errors) `None` is returned.
Returns the last observed watermark value, if available.
The [`Instant`] in the returned tuple is the approximate instant the
watermark was observed, allowing the caller to determine the staleness
of the value.

If the watermark value has yet to be observed  `None` is returned.
Returns the last observed watermark value if available . The [ ` Instant ` ] in the returned tuple is the approximate instant the watermark was observed allowing the caller to determine the staleness of the value . If the watermark value has yet to be observed ` None ` is returned .
pub fn cached_watermark(&self) -> Option<u64> {
        match self.last_watermark.load(Ordering::Relaxed) {
            // A value of 0 means "never observed a watermark".
            0 => None,
            v => Some(v),
        }
    }
pub fn cached_watermark ( & self ) -> Option < u64 > { match self . last_watermark . load ( Ordering :: Relaxed ) { // A value of 0 means "never observed a watermark". 0 => None , v => Some ( v ) , } }
Returns the last observed watermark value, if available.
Returns the last observed watermark value if available .
&self