mirror of
https://github.com/block/buzz.git
synced 2026-11-04 08:21:48 +00:00
d005c7bb9c
## Summary
Typeahead surfaces (the buzz-app and desktop topbars) send a NIP-50
search with `search_mode: "prefix"` whenever typing pauses. A one- or
two-character trailing `:*` prefix matches a large share of every
indexed message. The GIN index on `search_tsv` can't stop early or
return rows in rank order, so Postgres fetches, rechecks and ranks every
match before it applies `LIMIT`. In a large community, each of these
queries costs seconds of database CPU.
With this change, prefix-mode `search()` returns no hits when the
trailing whitespace token yields a lexeme shorter than three characters
(`PREFIX_MIN_CHARS`). The check runs inside the prefix tsquery SQL, on
the output of the same `to_tsvector('simple', …)` call that decides
which lexemes get `:*`. Punctuation therefore can't pad the count:
`pr.`, `@pr`, `#pr`, `c++`, `don't` and `pre-p` are all held back, and
`project ?` still runs, because `?` yields no `:*` lexeme. When the rule
applies, the tsquery is NULL, so it matches nothing and the GIN index
lookup returns no rows. Completed words in front of the trailing token
don't matter: `"the p"` runs the same broad `p:*` lookup as `"p"`.
Kind:0-only queries (profile typeahead) are exempt because there are few
profiles, and the short-name exact-lexeme ordering relies on one- and
two-character queries. `search_profile_names` is unchanged. Full-text
mode is unchanged.
Only the HTTP bridge (`POST /query` with `search_mode: "prefix"`)
reaches prefix mode. WebSocket REQ search always uses full-text mode, so
this change doesn't affect it.
## What got simpler
The kind:0-only predicate is now computed once (`profile_only`) and
shared by the new minimum and the existing exact-lexeme ordering. The
minimum lives in the one SQL fragment that already tokenizes the query,
so there is no second tokenizer in Rust to keep in sync with Postgres.
No new concepts beyond one constant.
## Known limits
- This bounds the worst case only. A common three-character prefix can
still match enough rows to be expensive. Bounding that needs a product
decision, such as a recency window for typeahead or a different index.
- Two-character CJK words (for example `東京`) get no message typeahead
until a third character. A trailing contraction or hyphenated word with
a short part (`don't`, `e-m`) gets none until the next word is started.
Full-text mode is unaffected.
- Clients should not show "no results" for one- and two-character input.
A client-side minimum is a companion change. That includes the legacy
desktop topbar in this repo (`desktop/src/features/search/hooks.ts`,
which searches at 2 characters globally and 1 in a channel); it is left
out here to keep this PR relay-only.
## Testing
- Extended
`prefix_mode_matches_final_token_prefix_without_changing_full_text` with
a table of prefix queries and the exact hit sets they must return. It
pins no hits for a trailing token that yields a lexeme below three
characters: alone, after a completed word (`project pr`), padded with
punctuation (`pr.`, `@pr`, `#pr`, `...p`), as a contraction (`don't`),
and hyphenated (`pre-p`). It covers `kinds = [9]`, no kinds, mixed `[0,
9]`, and `Newest` sort. Each of those rows has data it would match
without the minimum. The same table has controls that must still match:
`pro.`, `project ?` (punctuation-only trailing token), `pre-pro`, `t
pan` (a short completed word stays exact and isn't limited), and a
one-character kind:0 `p`. A full-text `don't` control shows that
full-text mode is unaffected.
`short_kind0_prefix_prioritizes_exact_lexeme_on_a_noisy_page` pins the
kind:0 exemption.
- Mutation-checked on Blox. Each of these fails a test: removing the
minimum, removing the kind:0 exemption, and applying the minimum to
every lexeme instead of only the trailing ones.
- Synthetic plan check on Blox Postgres (300k rows, GIN on a generated
`simple` tsvector, same `CROSS JOIN LATERAL` query shape). `'pr':*` took
3.6 s and read 10,411 buffers. The NULL tsquery took 0.01 ms: the bitmap
scan returned 0 rows and read no buffers.
- Two existing prefix tests used a two-character trailing token
(`project pl`, `alpha be`). They now use three or more characters
(`project plan`, `alpha bet`) and assert the same behavior.
- Blox: `cargo fmt --check`, `cargo clippy -p buzz-search --all-targets
-D warnings`, `buzz-search` unit tests, and the `buzz-search` Postgres
lane (`scripts/postgres-test-run.sh`).
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Signed-off-by: Luke Tornquist <tornquist@squareup.com>
Co-authored-by: Elrond <28d6302a099e5225b02c4155ac4236e4912603df2ab08dbfc2f4fef08ce598c8@buzz.block.builderlab.xyz>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>