Bank maintains state outside of Accounts

[aeyakovenko]

Problem

Due to rollback, any state outside of Accounts cannot be maintained as consistent. Any state must be computed from the Accounts structure from a desired checkpoint.

Proposed Solution

• move the state out of Bank
• write functions of the form fn compute_state(bank: &Bank) -> DesiredState

things that need to be moved:

• finality_time (this might be able to stay in the bank)
• account_subscriptions/signature_subscriptions (needs to specify confirmation depth?)
• leader_scheduler (should just be recomputed every time, this should only run once a day)
• storage_state (not sure)

tag: @mvines @carllin @CriesofCarrots @sakridge

[garious]

@aeyakovenko, have you seen test_hash_internal_state() in bank.rs? Specifically, are you looking for: (bank.last_id(), bank.hash_internal_state())?

[aeyakovenko]

@garious it is a bit more complicated. We basically need to define a TVU bank and a TPU bank. Which are the global bank state forks for those units. Computations that depend on either should reference those, but we also have some computation that is derived just from whatever fork is being proposed at the moment. To make it easier to manage this in a way that isn't tied to a specific consensus algorithm, the computations should just take a bank fork as a parameter.

[garious]

@rob-solana, I assigned this one to you under the assumption it's part of what you're already doing as part of taking over #2289.