Method observe

nodedb/src/engine/sparse/stats.rs:64–107

Update statistics with a new observed value. Call this on every write (PointPut) for each field in the document.

(&mut self, value: Option<&serde_json::Value>)

    ///
    /// Call this on every write (PointPut) for each field in the document.
    pub fn observe(&mut self, value: Option<&serde_json::Value>) {
        self.row_count += 1;

        match value {
            None | Some(serde_json::Value::Null) => {
                self.null_count += 1;
            }
            Some(val) => {
                self.non_null_count += 1;

                // Update min/max.
                let val_str = match val {
                    serde_json::Value::String(s) => s.clone(),
                    other => other.to_string(),
                };
                match &self.min_value {
                    None => self.min_value = Some(val_str.clone()),
                    Some(min) if val_str < *min => self.min_value = Some(val_str.clone()),
                    _ => {}
                }
                match &self.max_value {
                    None => self.max_value = Some(val_str.clone()),
                    Some(max) if val_str > *max => self.max_value = Some(val_str.clone()),
                    _ => {}
                }

                // Update HyperLogLog for cardinality estimation.
                let hash = crate::util::fnv1a_hash(val_str.as_bytes());
                let register_idx = (hash as usize) & (DEFAULT_HLL_M - 1);
                let remaining = hash >> DEFAULT_HLL_P;
                let leading_zeros = if remaining == 0 {
                    (64 - DEFAULT_HLL_P) as u8
                } else {
                    remaining.trailing_zeros() as u8 + 1
                };
                if leading_zeros > self.hll_registers[register_idx] {
                    self.hll_registers[register_idx] = leading_zeros;
                }

                // Re-estimate distinct count from HLL registers.
                self.distinct_count = self.hll_estimate();
            }
        }
    }

    /// HyperLogLog cardinality estimate.
    fn hll_estimate(&self) -> u64 {