Fix certain searches timing out when using sequential navigation (page=b1234).
The problem was that the so-called "small search optimization" (AKA: force Postgres
to use the tag index for small searches instead a sequential scan) wasn't triggering
because the ORDER BY clause for sequential navigation was `posts.id desc`, and we
were only checking for `posts.id DESC`.
This directory contains library code used through Danbooru. This includes things like defining API clients, dealing with
sources, parsing tag searches, storing and resizing images, and so on.
Many of the files here use the Service Object pattern. Instead of putting complex code in models or controllers, it goes
here, in plain old Ruby objects (POROs). This keeps models and controllers simpler, and keeps domain logic isolated and
independent from the database and the HTTP request cycle.
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