Relevance & BM25

Tachyon ranks results with BM25, a standard lexical relevance function: a document scores higher for a query term the more often that term appears in it, discounted by how common the term is across the whole collection and normalized for document length. It's the same family of scoring function used across most full-text search engines.

Every hit includes its score:

{ "document": { "id": "1", "title": "Wireless Mouse" }, "text_match": 554.788 }

text_match is also usable as a sort key — see _text_match in Sorting.

Per-field boosts

A field can carry an optional boost multiplier in its schema definition, increasing its contribution to a document's score relative to other fields:

{ "name": "title", "type": "text", "boost": 2.0 }

Query execution

For multi-term queries, Tachyon uses block-max WAND query pruning to skip over blocks of postings that can't possibly make the current top-K results, rather than scoring every candidate document exhaustively. This is a performance optimization, not a ranking difference — see Architecture → Query Pipeline for how it works.