Steve Howell d19c1f7438 message fetching: Avoid duplicate cache layers. ...

This code removes a lot of complexity with very likely
positive overall impact on system performance and
negligible downside.

We already cache display recipients on a per-user
level, so there's no need for another cache layer on
top of that that keys them with recipient ids.

We avoid strange things where Alice/Bob and Bob/Charlie
get put into the top layer cache and then we still have
a cache miss on Alice/Charlie despite the lower level
cache being able to support per-user lookups.

This change does introduce an extra database round trip
if any of our messages have a huddle, but the query is
extremely cheap, and we can always try to cache that
function more directly or try to re-use some of our
other huddle-based caches.

As part of this, we clean up the names for the
lower-level per-user cache of display recipients, and
we simplify the cache keys.

We also stop passing in a full Recipient object to the
`bulk_get_huddle_user_ids` functions.

The local impact of this change should be easy to
measure (at least approximately), since we use this
function every time a user gets messages via the
/messages endpoint.

2023-07-19 11:07:33 -07:00

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