Implement new Stake Pool Ranking formulas

[HeinrichApfelmus]

Issue number

ADP-1510, ADP-1491

Overview

In this pull request, we implement the new formulas for ranking stake pools. These comprise two numerical quantities and one notification message:

• currentROS = The return of stake (annualized) expected when delegating to the pool right now.
• saturationROS = The return of stake (annualized) expected when delegating to the pool if the pool were saturated and had 1/k of the total stake delegated to it, which is the ideal outcome for this pool in the future.
• A redelegation warning that encourages the user to redelegate to a different pool if the performance of the current pool becomes lackluster. Such a notification is necessary because the above rankings do not take into account block production performance.

While this pull request implements the formulas, it does not yet apply them to actual blockchain data, or expose them via the REST API; this is subject to future pull requests closely related to PR #2781.

However, this pull request also includes code for estimate the pool performance from past pool production data, so that these formulas can also be used in light-mode (Epic ADP-1422). This code was mostly copied from the existing implementation in the cardano-ledger repository.

Details

• Testing currentROS and saturationROS has been done manually, as there are no tests that are sufficiently independent of the definition.
• Likewise, the redelegation warning is hard to test, but basic sanity checks are performed to detect typos.
• Likewise, the performance estimation was tested manually on mainnet, and relies on past testing of the likelihood estimation code in the ledger.

Comments

• The "redelegation warning" was originally called "redelegation notification". I somehow started calling it a "warning". Is that good UX or does that contribute to "warning fatigue"?
• The present code does not yet consider warnings from past epochs. The specification is to make the warning sticky and also display it if it was triggered in one of the two previous epochs, but add a note in this case.
• The present code also does not yet take into account parameter changes that affect pool performance across epochs.

[HeinrichApfelmus]

bors try

[iohk-bors]

try

Build failed:

• ci/hydra-build:required

[rvl]

Looks great

[rvl]

Does this one need review as well?

[HeinrichApfelmus]

Nope, no need to worry about that one. Will be phased out anyway, and was taken from / tested in the (now stale) PR #2781

[rvl]

Can't remember why we didn't put an Integral instance on EpochNo. Enum is a bit yucky.
Could this be written shorter like this?

dt = fromIntegral $ fromEnum $ now - timeOfDelegation

[HeinrichApfelmus]

I'd love to, but EpochNo is a newtype on Word31, i.e. an unsigned integer. When testing unrelated stuff on checkpointing, I came to the conclusion that I should avoid the combination of unsigned integers and substraction like the plague. I'm using fromEnum because it gives a signed Int here, and then I feel more confident to subtract.

[HeinrichApfelmus]

bors merge

[iohk-bors]

Build succeeded:

• buildkite/cardano-wallet
• ci/hydra-build:required