Struct BlockImpact 

pub struct BlockImpact {
    pub max_tf: u32,
    pub min_len: u16,
}

One block’s impact pair: the two extremes that bound every posting in it.

Why a pair and not a stored score

A stored score is a number computed under one set of statistics. BM25’s score / ceiling is tf / (tf + k1 * (1 - b + b * len / avgdl)), so idf cancels but avgdl and (k1, b) do not: a bound sealed when documents were short falls below a true score once avgdl rises, and a bound sealed under beir() falls below one read under anserini(). Measured shortfalls were 15.21% and 19.56%.

A pair carries no statistics at all. term_score is monotone increasing in tf and monotone decreasing in len, so evaluating it at the block’s largest tf and shortest document dominates every posting in the block under ANY statistics and ANY (k1, b). The two extremes need not come from the same document; pairing them is looser than the true maximum and is therefore still an upper bound.

Fields

max_tf: u32

Largest term frequency in the block.

min_len: u16

Smallest document length in the block, saturating DOWN.

Implementations

impl BlockImpact

pub const fn from_meta(meta: &BlockMeta) -> Self

Reads the pair out of a persisted metadata row.

pub const fn is_absent(&self) -> bool

Returns true when the pair bounds nothing.

A real block has at least one posting, whose term frequency is at least one, so a zero max_tf can only mean the pair was never written — a version 1 stream, or a v2 stream missing an entry.

pub fn bound(&self, scorer: &TermScorer) -> f64

Evaluates the bound under the caller’s live scoring constants.

This is the whole remedy: the bound is computed HERE, at query time, from statistics that are current and parameters the caller chose.

Trait Implementations

impl Clone for BlockImpact

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for BlockImpact

impl Debug for BlockImpact

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

Formats the value using the given formatter.

impl Default for BlockImpact

fn default() -> Self

Returns the “default value” for a type.

impl Eq for BlockImpact

impl PartialEq for BlockImpact

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for BlockImpact