Query engine
Queries flow through Searcher::query. A Searcher owns reusable scratch buffers (a per-doc f32 accumulator with epoch-based dirty tracking, plus a Vec<u32> of touched doc ids), so successive queries do not re-allocate or zero 9k+ entries.
Query shape
#![allow(unused)]
fn main() {
pub struct Query {
pub text: Option<String>,
pub fuzzy: bool,
pub facets: FacetFilters,
pub numeric: NumericFilters,
pub sort: SortOrder,
pub limit: usize,
pub offset: usize,
pub count_facets: Vec<FacetAxis>,
}
}The wasm and REST surfaces both serialize this struct directly; both accept either text-only, filter-only, or combined queries. With no text, BM25 is skipped entirely and the engine sorts the filter intersection by the chosen SortOrder.
Sort orders
| Variant | Behavior |
|---|---|
Relevance | BM25 with PageRank tiebreak. Falls back to PageRankDesc when no text query is present. |
PageRankDesc | Sort by precomputed PageRank, descending. Used for browse-style listings. |
FceHrsPerWeekAsc | Lightest workload first, requires the FCE hours field to be present. |
FceInterestDesc, FceOverallTeachingDesc | FCE rating ranks. |
CourseNumAsc, CodeAsc | Alphabetical / numeric on the course identifier. |
Score blending
For text queries, BM25 scores from the postings layer multiply by 1 + alpha * pagerank_normalized with alpha = 0.2. PageRank breaks ties on otherwise equal BM25, so algorithms shows 15-451 ahead of an obscure 1-credit elective with the same baseline score. Pure browse (no text) uses raw PageRank descending.
Top-K early termination
With Relevance sort and a known limit, the engine maintains a BinaryHeap<(NotNan<f32>, doc_id)> of size limit and prunes any candidate whose maximum possible remaining score cannot displace the current heap minimum. For typical limits (10-50), the heap kicks in almost immediately and the linear pass over candidates short-circuits.
Facet counts and “did you mean”
When count_facets is non-empty, the engine produces per-axis tallies after applying the filter intersection. Counts are smart-pruned (sorted by size, capped at 100). The did_you_mean_codes field on the result populates when the literal query parses as a course code and one or more digit permutations of the trailing identifier match courses in the catalog (15-122 returning 15-122 and 15-127 for example).
Result cache
Searcher::with_cache_capacity enables an LRU result cache keyed by the bincode-serialized Query. Cache hits skip the entire query pipeline and return a clone of the previous result. Cache size is per-searcher and explicit; the wasm surface uses a 64-entry cache and the REST API a larger one.