Struct CostEstimator 

pub struct CostEstimator {
    pub byte_budget: usize,
    pub corpus: usize,
    pub vector_bytes: usize,
}

Byte-budget cost model estimator for vector filter strategies (§5.3, D-007).

The 0.4.5–0.5.4 version of this type carried a byte_budget field it never read and branched on candidate_count against two hard-coded thresholds (500, 5000) — D-007’s interface with none of D-007’s mechanism. It now prices both strategies in bytes and takes the minimum, and byte_budget is a hard ceiling on the candidate set rather than an unused field.

Fields

byte_budget: usize

corpus: usize

Corpus size: how many vectors the model holds. Sets selectivity, and so the k′ inflation.

vector_bytes: usize

Bytes per stored vector, from the model’s declared dimension (D-037).

Implementations

impl CostEstimator

pub fn new(byte_budget: usize, corpus: usize, vector_bytes: usize) -> Self

pub fn k_prime(&self, k: usize, candidates: usize) -> usize

The k′ PostFilter must request to expect k survivors.

Selectivity is candidates / corpus, so k′ = k × corpus / candidates. Clamped to the corpus: asking the index for more rows than exist is not an error but it is not an estimate either, and letting it run away makes the cost comparison meaningless for tight filters — which is precisely when the comparison matters.

pub fn estimate( &self, k: usize, candidates: CandidateCount, ) -> Result<CostEstimate>

Price both strategies and take the minimum (§5.3, D-007).

Strategy	Estimated bytes
PostFilter	k′ × (vector_bytes + row_bytes) + the filter pass
PreFilterCTE	the filtered scan + candidates × vector_bytes

The filter pass is common to both — the traversal has to run either way — so it appears in both rows and cancels out of the comparison. It is included anyway, because the budget ceiling is checked against an absolute figure and a cost model that omits a term it “knows” cancels is a cost model that lies the moment someone adds a third strategy.

Trait Implementations

impl Clone for CostEstimator

fn clone(&self) -> CostEstimator

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for CostEstimator

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

Formats the value using the given formatter.