Summary:
Ref T11954. Depends on D16993. We have a couple of "look up the class for this key" queries which are costly enough to show up on a profile.
These aren't huge wins, but they're pretty easy. We currently do this like this:
```
$class_map = load_every_subclass();
return idx($class_map, $key);
```
However, we don't need to load EVERY subclass if we're only looking for, say, the Conduit method subclass which implements `user.whoami`. This allows us to cache that map and find the right class efficiently.
This cache is self-validating and completely safe even in development.
Test Plan:
- Used `curl` to make queries to `user.whoami`, verified that content was identical before and after the change.
- Used `ab -n100` to roughly measure 99th percentile time, which dropped from 74ms to 65ms. This is a small improvement (13% in the best case, here) but it benefits every Conduit method call.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T11954
Differential Revision: https://secure.phabricator.com/D16994
