Alternative Algorithm Implementation

[Kache]

Playing around with this concept myself, I'd like to suggest the following implementation:

def xfetch_early?(ttl:, compute_time:, beta: 1.0)
  Kernel.rand < Math::E ** -(ttl.to_f / compute_time / beta)
end

def original_xfetch_api(expiry, delta:, beta: 1.0)
  # original: Time.now - (delta * beta * Math.log(rand)) >= expiry
  xfetch_early?(expiry - Time.now, compute_time: delta, beta: beta)
end

1. implement using the algorithm's inverse, which is more declarative.
2. the instant probability over ttl, e.g. e^(-ttl/5.0) becomes easy to graph and understand
3. xfetch_early? is static/pure, having no dependency on Time
4. it's time-unit agnostic, use secs, msecs, minutes, etc for ttl and compute_time