`library::local_original_count` feeds the "On this device" chip and runs
beside the rating counts on every star keystroke. On the reference library
it cost 1.3-1.4 ms best-of-50 (3 ms on a busy machine) to find 254
originals among 19,000 visible images.
It was a correlated EXISTS per visible image:
SCAN i USING INDEX images_grid_order
SEARCH ic EXISTS USING INTEGER PRIMARY KEY (rowid=?)
`image_cache` holds a row only for what has been fetched, so the question
is driven from it: `i.id IN (SELECT image_id FROM image_cache WHERE
tier_actual >= Original)`, which SQLite plans as the list first and a probe
of `images` by id for each entry:
SEARCH i USING INTEGER PRIMARY KEY (rowid=?)
LIST SUBQUERY 1
SCAN image_cache
`image_id` is the cache's primary key, so each image is in the list at most
once and the count is the one the EXISTS gave (254). After: 0.05 ms. On a
library whose every original is cached this is as much work as before,
which is the proportion the rule asks for.
The count stays on the keystroke path: dropping it there would leave the
chip stale after a background download until something else refreshed it,
and at this cost there is nothing left to save. catalog_bench spells the
query as dr-ui does, so its copy changes with it.
dtourolle
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