nomination-pools: add optional commission

[kianenigma]

Currently, we don't have commission, and we prefer to keep the code simple and ship without this. Nonetheless, it is reasonable to add an optional commission for pool operators.

[Szegoo]

I have a couple of questions about this issue.

If I understand this correctly by pool operators you mean all the pool roles inside the PoolRoles struct?

• Do all of the administrative roles get the commission? Maybe we could make choosing who receives a commission configurable(e.g setting that only the nominator gets the commission). Also, do all of them get the same share of the commission? That should probably also be configurable.
• I assume that the commission is taken from the earned rewards.

[kianenigma]

Do all of the administrative roles get the commission? Maybe we could make choosing who receives a commission configurable(e.g setting that only the nominator gets the commission). Also, do all of them get the same share of the commission? That should probably also be configurable.

Yeah it can probably be configurable.

I assume that the commission is taken from the earned rewards.

Correct.

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Note that I would not start working on this yet, as Pools are not launched yet in Polkadot and it is more reasonable to keep them simple at the beginning.

[Szegoo]

Ok, I will start working on this when the pools are launched in Polkadot.

[kianenigma]

Some notes, I propose we re-think the commission and not make it be a "free forever commission" system like staking. Instead, each pool member can set two commission values:

struct Commission {
  current: Percent
  max_ever: Option<Percent>,
} 

impl Default for Commission {
  fn default() -> Self {
    current: Percent::zero(),
    max_ever: None,
  }
}

with the following rules:

1. current can NEVER be set to a value more than max_ever.
2. max_ever can never be increased.

[kianenigma]

A rate limit on the maximum change is also a good idea.

[Szegoo]

Instead, each pool member can set two commission values:

Shouldn't these two values be set by the pool operators?