Struct DatasetStatistics 

pub struct DatasetStatistics { /* private fields */ }

Dataset-level statistics aggregating per-predicate histograms.

Provides the interface expected by the cost-based optimizer for pattern cardinality estimation.

Implementations

impl DatasetStatistics

pub fn new() -> Self

Create a new empty statistics store with the default bucket count (100).

pub fn with_num_buckets(num_buckets: usize) -> Self

Create a new statistics store with a custom bucket count.

pub fn record_triple(&mut self, predicate: &str, object: &str)

Record the insertion of a single triple (subject, predicate, object).

Updates global counts and incrementally updates the per-predicate histogram.

pub fn get_histogram(&self, predicate: &str) -> Option<&PredicateHistogram>

Return the histogram for predicate, if one exists.

pub fn estimate_pattern_cardinality( &self, subject: Option<&str>, predicate: Option<&str>, object: Option<&str>, ) -> u64

Estimate the cardinality of the triple pattern (?s, predicate?, object?).

Pattern selectivity is computed as:

• Unknown subject and unknown predicate → total_triples.
• Known predicate, unknown object → histogram.total_count.
• Known predicate + known object → equality filter estimate.
• Known object, unknown predicate → brute-force across all histograms.
• Unknown predicate and unknown object → total_triples.

pub fn rebuild_histograms(&mut self, values: &[(String, String)])

Rebuild all histograms from a full scan of (predicate, object) pairs.

This is an expensive O(n log n) operation and should be run during off-peak periods or triggered by the auto-analyze subsystem.

pub fn total_triples(&self) -> u64

Return the total number of triples tracked by these statistics.

pub fn set_distinct_subjects(&mut self, count: u64)

Update the known distinct subject count.

Called by the store layer after it recomputes subject cardinality.

pub fn set_distinct_objects(&mut self, count: u64)

Update the known distinct object count.

pub fn last_updated(&self) -> Instant

Return when the statistics were last updated.

pub fn predicate_count(&self) -> usize

Return the number of predicates with histograms.

Trait Implementations

impl Default for DatasetStatistics

fn default() -> Self

Returns the “default value” for a type.