Strange issue with sidekiq 4.0

[ixti]

It seems like throttle keys are not properly evicted.

After upgrade we saw strange behavior when amount of throttled jobs was higher than amount of busy workers and was not going down.

[ixti]

After investigation, it seems like this is absolutely legit, due to nature of how stats are collected.
Our stats are pretty simple, and have complexity of O(1) (if either :concurrency or :throttle only limit given) or O(2) (if both :concurrency and :throttle limits are given) per throttle key (worker class in most cases):

• to get :threshold current volume we use LLEN
• to get :concurrency current volume we use SCARD

Stats of sidekiq are calculated using way more complex logic.