Previously cached counting made redis calls in main thread and performed
the flush in main thread.
This could lead to pathological states in extreme heavy load.
This refactor reduces load and cleans up the interface
Previously we were calling `EXPIRE` every time we incremented a given key. Instead, we can call EXPIRE once when the key is first populated. A LUA script is used to make this as efficient as possible.
Consumers of this Concern use daily keys. Since we're now calling EXPIRE only at the beginning of the day, rather than throughout the day, the expire time has been increased from 3 to 4 days.
Doing .pluck(:column).first is a very common pattern in Discourse and in
most cases, a limit cause isn't being added. Instead of adding a limit
clause to all these callsites, this commit adds two new methods to
ActiveRecord::Relation:
pluck_first, equivalent to limit(1).pluck(*columns).first
and pluck_first! which, like other finder methods, raises an exception
when no record is found
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
