each process has a local setting cache (hashtable of name to content)

• when process starts we load all settings and populate the cache, and save cache_refreshed_at time
• on each request, we do a query that joins on log (or uses updated_at or revisions) to load all settings cards which have changed since last cache_refreshed_at.  we update the cache for all those settings
• setting lookup can now just look in the hashtable for values.