Difference between weight, current_weight, effective_weight, etc?

[Pablo Fischer]

Howdy!

We are looking (unless it already exists) to add load feedback
functionality to our setup, this basically means to have an API
(either lua or through C) that we can use to change the weight of
servers "dynamically" (either async or by hitting a specific URL).

However when reading the code I'm a little confused on the difference
between those weight variables, seems that sometimes you compare them
against each other so not sure what is the difference in them.

What is the difference between weight, current_weight and
effective_weight? I'm assuming that total_weight is the sum of all
weights (weight?) for a given upstream.

Thanks!
-- 
Pablo