Figuring out what unread topics a user has is a very expensive
operation over time.
Users can easily accumulate 10s of thousands of tracking state rows
(1 for every topic they ever visit)
When figuring out what a user has that is unread we need to join
the tracking state records to the topic table. This can very quickly
lead to cases where you need to scan through the entire topic table.
This commit optimises it so we always keep track of the "first" date
a user has unread topics. Then we can easily filter out all earlier
topics from the join.
We use pg functions, instead of nested queries here to assist the
planner.
It should update the topic subscription so long as what is being requested is higher than what is currently set for the user and the given topic
It should not update the topic subscription if the requested subscription is less than what is currently set for the user and given topic
This feature introduces the concept of themes. Themes are an evolution
of site customizations.
Themes introduce two very big conceptual changes:
- A theme may include other "child themes", children can include grand
children and so on.
- A theme may specify a color scheme
The change does away with the idea of "enabled" color schemes.
It also adds a bunch of big niceties like
- You can source a theme from a git repo
- History for themes is much improved
- You can only have a single enabled theme. Themes can be selected by
users, if you opt for it.
On a technical level this change comes with a whole bunch of goodies
- All CSS is now compiled using a custom pipeline that uses libsass
see /lib/stylesheet
- There is a single pipeline for css compilation (in the past we used
one for customizations and another one for the rest of the app
- The stylesheet pipeline is now divorced of sprockets, there is no
reliance on sprockets for CSS bundling
- CSS is generated with source maps everywhere (including themes) this
makes debugging much easier
- Our "live reloader" is smarter and avoid a flash of unstyled content
we run a file watcher in "puma" in dev so you no longer need to run
rake autospec to watch for CSS changes
