Struct RelationStats 

pub struct RelationStats {
    pub rel_id: RelId,
    pub cardinality: u64,
    pub byte_size: u64,
    pub column_stats: Vec<ColumnStats>,
    pub prefix_degrees: Vec<PrefixDegreeStats>,
    pub key_heats: Vec<KeyHeatStats>,
    pub heat: f32,
    pub last_access: u64,
    pub has_index: bool,
}

GPU-resident relation statistics.

Tracks cardinality, memory usage, access patterns, and column-level statistics for relations stored on the GPU. These statistics drive optimizer cost models and solver heuristics for efficient query execution.

Fields

rel_id: RelId

Unique identifier for the relation

cardinality: u64

Estimated number of rows in the relation

byte_size: u64

Estimated total size in bytes on GPU

column_stats: Vec<ColumnStats>

Per-column statistics

prefix_degrees: Vec<PrefixDegreeStats>

Per-column prefix fan-out statistics for trie-style WCOJ planning.

key_heats: Vec<KeyHeatStats>

Per-column key heat/skew summaries for skew-aware WCOJ planning.

heat: f32

Access heat for LRU-style eviction (exponential moving average)

last_access: u64

Unix timestamp of last access

has_index: bool

Whether an index exists for this relation

Implementations

impl RelationStats

pub fn new(rel_id: RelId) -> Self

Creates new statistics for a relation with default (empty) values.

Arguments

• rel_id - The unique identifier for the relation

Returns

A new RelationStats instance with zero cardinality, no columns, and cold heat.

pub fn update_cardinality(&mut self, rows: u64)

Updates the cardinality (row count) of the relation.

This should be called after bulk loads, inserts, or when statistics are refreshed from the actual GPU-resident data.

Arguments

• rows - The new cardinality estimate

pub fn update_byte_size(&mut self, bytes: u64)

Updates the byte size estimate for the relation.

Arguments

• bytes - The estimated total size in bytes

pub fn record_access(&mut self)

Records an access to this relation, updating heat and timestamp.

Uses an exponential moving average for heat calculation: heat = heat * 0.9 + 0.1

This causes frequently accessed relations to maintain high heat while infrequently accessed ones cool down over time.

pub fn decay_heat(&mut self, factor: f32)

Decays the heat by a multiplicative factor.

This should be called periodically (e.g., during garbage collection or memory pressure events) to allow unused relations to cool down.

Arguments

• factor - Multiplicative decay factor (typically 0.0 to 1.0)

pub fn add_column(&mut self, col_stats: ColumnStats)

Adds column statistics for a new column.

Arguments

• col_stats - The column statistics to add

pub fn get_column(&self, col_idx: usize) -> Option<&ColumnStats>

Gets column statistics by index.

Arguments

• col_idx - The column index

Returns

A reference to the column statistics if found

pub fn get_column_mut(&mut self, col_idx: usize) -> Option<&mut ColumnStats>

Gets mutable column statistics by index.

Arguments

• col_idx - The column index

Returns

A mutable reference to the column statistics if found

pub fn add_prefix_degree(&mut self, prefix_degree: PrefixDegreeStats)

Adds prefix-degree statistics for a join-key column.

Existing entries for the same column are retained; consumers use the first matching entry so snapshots can preserve historical observations.

pub fn get_prefix_degree(&self, col_idx: usize) -> Option<&PrefixDegreeStats>

Gets prefix-degree statistics by column index.

pub fn add_key_heat(&mut self, key_heat: KeyHeatStats)

Adds key-heat statistics for a join-key column.

This is distinct from relation-level RelationStats::heat: relation heat tracks access frequency, while key heat tracks per-key skew for a column.

pub fn get_key_heat(&self, col_idx: usize) -> Option<&KeyHeatStats>

Gets key-heat statistics by column index.

pub fn estimate_selectivity(&self, estimated_matches: u64) -> f64

Estimates the selectivity for a given predicate cardinality.

Arguments

• estimated_matches - The estimated number of matching rows

Returns

The selectivity as a ratio (0.0 to 1.0)

Trait Implementations

impl Clone for RelationStats

fn clone(&self) -> RelationStats

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for RelationStats

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

Formats the value using the given formatter.