`keywords::list` is the vocabulary with a per-word photograph count, and
`keywords::for_images` calls it on every selection change to redraw the
keyword panel. On the reference library (58 words, 10,800 assignments) it
cost 3.0-3.5 ms best-of-50 by catalog_bench, `for_images` 3.1-3.6 ms (6 and
5 ms on a busy machine).
Per word, the count walks `keywords_term (keyword)` and, for each
assignment, reads the `keywords` row to learn its version before probing
`versions` for the image:
SEARCH k USING INDEX keywords_term (keyword=?)
SEARCH v USING INTEGER PRIMARY KEY (rowid=?)
With `keywords_term_version (keyword, version_id)` the first step is
index-only:
SEARCH k USING COVERING INDEX keywords_term_version (keyword=?)
SEARCH v USING INTEGER PRIMARY KEY (rowid=?)
After: `list` 1.3 ms, `for_images` 1.5 ms, with the same answers (digests of
both outputs compared on the reference library).
The index is created on first use by `list`, with CREATE INDEX IF NOT EXISTS,
not by a migration: a new schema version makes every older build refuse this
catalog's snapshot at sync (`sync::remote_is_mergeable` compares
`user_version` and nothing else), and a build that meets an extra index
ignores it. Once the index exists the statement is a schema lookup, 8 us. A
failure to create it -- a read-only or busy catalog -- is logged and the
list is read without it, as before.
dtourolle
d537e4a965