Timezone-appropriate greeting, wikitech!

I've been working on a new extension, BetaFeatures[0]. A lot of you have heard about it through the grapevine, and for the rest of you, consider this an announcement for the developers. :)

The basic idea of the extension is to enable features to be enabled experimentally on a wiki, on an opt-in basis, instead of just launching them immediately, sometimes hidden behind a checkbox that has no special meaning in the interface. It also has a lot of cool design work on top of it, courtesy of Jared and May of the WMF design team, so thanks very much to them. There are still a few[1] things[2] we have to build out, but overall the extension is looking pretty nice so far.

I am of course always soliciting advice about the extension in general, but in particular, we have a request for a feature for the fields that has been giving me a bit of trouble. We want to put a count of users that have each preference enabled on the page, but we don't want to, say, crash the site with long SQL queries. Our theories thus far have been:

* Count all rows (grouped) in user_properties that correspond to properties registered through the BetaFeatures hook. Potentially a lot of rows, but we have at least decided to use an "IN" query, as opposed to "LIKE", which would have been an outright disaster. Obviously: Caching. Caching more would lead to more of the below issues, though.

* Fire off a job, every once in a while, to update the counts in a table that the extension registers. Downsides: Less granular, sort of fakey (since one of the subfeatures will be incrementing the count, live, when a user enables a preference). Upside: Faster.

* Update counts with simple increment/decrement queries. Upside: Blazingly faster. Potential downside: Might get out of sync. Maybe fire off jobs even less frequently, to ensure it's not always out of date in weird ways?

So my question is, which of these are best, and are there even better ways out there? I love doing things right the first time, hence my asking.

[0] https://www.mediawiki.org/wiki/Extension:BetaFeatures [1] https://mingle.corp.wikimedia.org/projects/multimedia/cards/2 [2] https://mingle.corp.wikimedia.org/projects/multimedia/cards/21

P.S. One of the first features that we'll launch with this framework is the "MultimediaViewer" extension which is also under[3] development[4] as we speak. Exciting times for the Multimedia team!

[3] https://mingle.corp.wikimedia.org/projects/multimedia/cards/8 [4] https://mingle.corp.wikimedia.org/projects/multimedia/cards/12