Landing on a photograph in develop opens the catalog once to fetch the
original and once more per prefetched neighbour to ask whether the cache
already holds it: five opens, each running the whole backfill. The bench
timed one open but not the landing, so the cost of the shape was not
visible and a fix to it could not be measured.
Two figures now, both against an empty cache so the question is asked the
same way whatever the answer: the five-open shape the app had, and the
two-open shape where the prefetch worker keeps one connection for its
batch. On a copy of the reference catalog (23,582 images) under load, the
five-open landing costs ~80 ms of CPU.
dtourolle
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