hybrid_search rebuilt the BM25 index from scratch (re-tokenising every record)
and rewrote the whole .h5 file on every single query, so a query cost O(store
size) in both CPU and disk I/O. Steady-state p50 per the search harness:
5.5 -> 0.24 ms (1K), 49 -> 2.1 ms (10K), 884 -> 23 ms (100K).
- BM25Index is incremental: add_document / remove_document keep it exactly
equivalent to a fresh build over the same live documents (property test: 60
random op sequences compared against BM25Index::build after every step). IDF
moves to query time since it depends on the live document count. Top-k uses
a bounded heap, ties break by doc id (results were HashMap-ordered), and the
"WAND" code that computed a bound and then discarded it is removed.
- HDF5Memory keeps one index for its lifetime, built lazily. Appends are
picked up by ensure_bm25_fresh whatever path added them; delete and in-place
update report themselves; compaction drops the index. A test drives every
mutation and compares against a fresh build.
- A query no longer calls flush(). Activation boosts are marked dirty and
persisted by the next checkpoint, including a best-effort one on drop so a
search-only session keeps them (approved behaviour change). Activation
weights are capped at 16.0; they previously grew without bound.
The archived mission branch's BM25 cache was reviewed and not used: it was
invalidated by every write, so interleaved save/search still rebuilt per
query, and it changed the default fusion weights.
Co-Authored-By: Claude Fable 5.1 <[email protected]>
