Struct EquiDepthHistogram 

pub struct EquiDepthHistogram { /* private fields */ }

An equi-depth histogram for selectivity estimation.

Equi-depth histograms partition data into buckets where each bucket contains approximately the same number of rows. This provides more accurate selectivity estimates than assuming uniform distribution, especially for skewed data.

Example

use grafeo_engine::query::optimizer::cardinality::EquiDepthHistogram;

// Build a histogram from sorted values
let values = vec![1.0, 2.0, 3.0, 4.0, 5.0, 10.0, 20.0, 30.0, 40.0, 50.0];
let histogram = EquiDepthHistogram::build(&values, 4);

// Estimate selectivity for age > 25
let selectivity = histogram.range_selectivity(Some(25.0), None);

Implementations

impl EquiDepthHistogram

pub fn new(buckets: Vec<HistogramBucket>) -> Self

Creates a new histogram from pre-built buckets.

pub fn build(values: &[f64], num_buckets: usize) -> Self

Builds an equi-depth histogram from a sorted slice of values.

Arguments

• values - A sorted slice of numeric values
• num_buckets - The desired number of buckets

Returns

An equi-depth histogram with approximately equal row counts per bucket.

pub fn num_buckets(&self) -> usize

Returns the number of buckets in this histogram.

pub fn total_rows(&self) -> u64

Returns the total number of rows represented.

pub fn buckets(&self) -> &[HistogramBucket]

Returns the histogram buckets.

pub fn range_selectivity(&self, lower: Option<f64>, upper: Option<f64>) -> f64

Estimates selectivity for a range predicate.

Arguments

• lower - Lower bound (None for unbounded)
• upper - Upper bound (None for unbounded)

Returns

Estimated fraction of rows matching the range (0.0 to 1.0).

pub fn equality_selectivity(&self, value: f64) -> f64

Estimates selectivity for an equality predicate.

Uses the distinct count within matching buckets for better accuracy.

pub fn min_value(&self) -> Option<f64>

Gets the minimum value in the histogram.

pub fn max_value(&self) -> Option<f64>

Gets the maximum value in the histogram.

Trait Implementations

impl Clone for EquiDepthHistogram

fn clone(&self) -> EquiDepthHistogram

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for EquiDepthHistogram

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

Formats the value using the given formatter.