Struct PrefixDegreeStats 

pub struct PrefixDegreeStats {
    pub col_idx: usize,
    pub avg_degree: f64,
    pub max_degree: f64,
}

Prefix fan-out statistics for one relation column.

WCOJ planners use this as the trie prefix-degree signal: lower average and bounded maximum fan-out usually mean less inner-loop work for a variable order that binds the column early.

Fields

col_idx: usize

Column index within the relation.

avg_degree: f64

Average number of rows below one distinct prefix key.

max_degree: f64

High-water fan-out used as a skew guard.

Implementations

impl PrefixDegreeStats

pub fn new(col_idx: usize, avg_degree: f64, max_degree: f64) -> Self

Creates prefix-degree statistics for a column.

Trait Implementations

impl Clone for PrefixDegreeStats

fn clone(&self) -> PrefixDegreeStats

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for PrefixDegreeStats

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.