Struct Histogram 

pub struct Histogram {
    pub buckets: Vec<HistogramBucket>,
    pub total_count: u64,
    pub incremental_updates: u64,
    pub stale: bool,
}

Equi-depth histogram for column value distribution estimation.

Buckets are sorted by lower_bound and non-overlapping. The CBO uses binary search (O(log B)) on bucket boundaries for all selectivity lookups.

Fields

buckets: Vec<HistogramBucket>

Ordered, non-overlapping histogram buckets.

total_count: u64

Total number of rows represented by this histogram (sum of all bucket counts).

incremental_updates: u64

Cumulative number of incremental updates since last full ANALYZE.

stale: bool

Whether the histogram is considered stale (updates > 20% of total_count).

Implementations

impl Histogram

pub fn find_bucket(&self, value: f64) -> Option<usize>

Finds the bucket index containing value via binary search.

Returns the index of the bucket whose range [lower_bound, upper_bound) contains value. Returns None if value is outside all bucket ranges.

Complexity: O(log B) where B = number of buckets. No allocations.

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

Estimates equality selectivity for a given value.

If the value falls within a bucket with distinct_count > 0, returns bucket.count / (bucket.distinct_count × total_count). If distinct_count == 0 or value is outside all buckets, returns 1 / total_count. Returns 0.0 when total_count == 0. Result is clamped to [0.0, 1.0].

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

Estimates less-than selectivity for a given value.

Sums counts of all buckets fully below value, plus linear interpolation of the partial bucket containing value. Divides by total_count. Returns 0.0 if value ≤ first bucket lower bound, 1.0 if value ≥ last bucket upper bound. Result is clamped to [0.0, 1.0].

pub fn estimate_range_selectivity(&self, low: f64, high: f64) -> f64

Estimates range selectivity for [low, high].

Sums full buckets within the range plus interpolates boundary buckets. Returns 0.0 if low > high or range is outside the histogram. Returns 1.0 if range encompasses the entire histogram. Result is clamped to [0.0, 1.0].

pub fn increment_bucket(&mut self, value: f64)

Increments the count of the bucket containing value.

Finds the bucket via binary search and increments its count by 1. Increments incremental_updates by 1. If incremental_updates exceeds 20% of total_count, marks the histogram as stale. No-op if value is outside all bucket ranges.

pub fn decrement_bucket(&mut self, value: f64)

Decrements the count of the bucket containing value, floored at zero.

Finds the bucket via binary search and decrements its count by 1 (minimum 0). Increments incremental_updates by 1. Checks staleness. No-op if value is outside all bucket ranges.

Trait Implementations

impl Clone for Histogram

fn clone(&self) -> Histogram

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Histogram

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

Formats the value using the given formatter.

impl Default for Histogram

fn default() -> Histogram

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for Histogram

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl PartialEq for Histogram

fn eq(&self, other: &Histogram) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for Histogram

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for Histogram