The product's own search answered in p50 20.16s on 165,973 atoms. The SQL
rewrite brought that to 0.68s; this brings it to 57ms and says why the rest was
there.
The cost was not SQL. An OR MATCH scores every row it touches, and a question
carries words the whole library carries: `"parsing"* OR "error"* OR "in"* OR
"the"* OR "pdf"* OR "converter"*` matched 127,145 atoms and took 305ms, while a
CJK bigram phrase query with 32 matches took 1.0ms. Latency tracked match count.
- text_index.rare_terms asks the index which of its own words are noise: count
each term, drop the ones over 5% of the library, keep the rarest few when all
of them are common. No stop-word list; a corpus of PDFs and a corpus of shell
history get different answers. 0.05 is swept, not chosen — on n=173
recall@10 peaks there (0.899 / p50 58.6ms) against 0.893 / 112.9ms at 0.20
and 0.844 / 13.4ms at 0.01.
- The bound is a cost, not a claim about rarity: `cap = max(int(total*fraction)+1, 2)`,
so a word matching one atom in eleven is kept — scoring one candidate is free.
A capped count cannot rank words that all saturate, so those few are counted
exactly.
- Schema v6 adds `term_df`: a word is counted once and the next question pays
nothing. Every atom write clears it, so a stored count cannot outlive the
library it described. Cold p50 73ms, warm 63ms, 1,324 terms cached.
- The denominator is `count(*) FROM atoms` (0.01ms) rather than
`count(*) FROM atom_fts` (37ms cold): FTS rows are written and deleted with
their atoms, so the two counts move together and only one of them is free.
SCALE.md, idle machine (load 1.76, 32 cores, 4 threads per query):
165,973 atoms — 1.66x the contract's 100k — 300 probes, p50 57ms, p95 138ms.
Against the frozen baseline of 20.16s that is 354x. Holder-scoped (n=173):
recall@10 0.870, MRR 0.740, p50 62ms.
Verification: pytest backend/tests bench/tests -q -> 173 passed (5 new
text_index tests: the common word is dropped and the rare one still answers, an
all-common query keeps its rarest words in order, a one-word query is never
filtered, an empty library keeps everything, and a write voids the counts);
ruff clean; mypy fresh cache clean; pyright 0 errors on the touched files.
