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staking: groundwork to make end-epoch processing faster
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We have almost completed a rework of the data modeling
at the epoch boundary which will let us use `Joinset` on
commutative operations like delegation change tallying
and validator state processing.
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@erwanor
erwanor committed Feb 23, 2024
1 parent 937814d commit 2d4091d
Showing 1 changed file with 55 additions and 49 deletions.
104 changes: 55 additions & 49 deletions crates/core/component/stake/src/component/epoch_handler.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -45,7 +45,7 @@ pub trait EpochHandler: StateWriteExt + ConsensusIndexRead {
let mut num_undelegations = 0usize;

// TODO(erwan): we can turn this into a joinset later, but since the storage locality is pretty good
// and the number of ticks is about 700, we can just do this in a loop for now.
// and the number of ticks is about ~700, we can just do this in a loop for now.
for height in epoch_to_end.start_height..=end_height {
let changes = self
.get_delegation_changes(
Expand Down Expand Up @@ -86,6 +86,9 @@ pub trait EpochHandler: StateWriteExt + ConsensusIndexRead {
"collected delegation changes for the epoch"
);

// Compute and set the chain base rate for the upcoming epoch.
let next_base_rate = self.process_chain_base_rate().await?;

// TODO(erwan): no doubt, this can be optimized, but we're on a cold path and for now,
// we want the simplest possible implementation.
let delegation_set = delegations_by_validator
Expand Down Expand Up @@ -113,57 +116,9 @@ pub trait EpochHandler: StateWriteExt + ConsensusIndexRead {
.union(&consensus_set)
.collect::<BTreeSet<_>>();

// We are transitioning to the next epoch, so the "current" base rate in
// the state is now the previous base rate.
let prev_base_rate = self.get_current_base_rate().await?;

tracing::debug!(
"fetching the issuance budget for this epoch from the distributions component"
);
// Fetch the issuance budget for the epoch we are ending.
let issuance_budget_for_epoch = self
.get_staking_token_issuance_for_epoch()
.expect("issuance budget is always set by the distributions component");

// Compute the base reward rate for the upcoming epoch based on the total amount
// of active stake and the issuance budget given to us by the distribution component.
let total_active_stake_previous_epoch = self.total_active_stake().await?;
tracing::debug!(
?total_active_stake_previous_epoch,
?issuance_budget_for_epoch,
"computing base rate for the upcoming epoch"
);

let base_reward_rate =
U128x128::ratio(issuance_budget_for_epoch, total_active_stake_previous_epoch)
.expect("total active stake is nonzero");
let base_reward_rate: Amount = (base_reward_rate * *FP_SCALING_FACTOR)
.expect("base reward rate is around one")
.round_down()
.try_into()
.expect("rounded to an integral value");
tracing::debug!(%base_reward_rate, "base reward rate for the upcoming epoch");

let next_base_rate = prev_base_rate.next_epoch(base_reward_rate);
tracing::debug!(
?prev_base_rate,
?next_base_rate,
?base_reward_rate,
?total_active_stake_previous_epoch,
?issuance_budget_for_epoch,
"calculated base rate for the upcoming epoch"
);

// Set the next base rate as the new "current" base rate.
self.set_base_rate(next_base_rate.clone());
// We cache the previous base rate in the state, so that other components
// can use it in their end-epoch procesisng (e.g. funding for staking rewards).
self.set_prev_base_rate(prev_base_rate.clone());

let mut funding_queue: Vec<(IdentityKey, FundingStreams, Amount)> = Vec::new();

for validator_identity in validators_to_process {
// TODO(erwan): we don't need to remove the entry in prod, this is just for testing.
let total_delegations = delegations_by_validator
.remove(validator_identity)
.unwrap_or_else(Amount::zero);
Expand All @@ -172,6 +127,7 @@ pub trait EpochHandler: StateWriteExt + ConsensusIndexRead {
.remove(validator_identity)
.unwrap_or_else(Amount::zero);

// These operations should be commutative, so later, we can consider using a Joinset for this loop.
if let Some(rewards) = self
.process_validator(
validator_identity,
Expand Down Expand Up @@ -414,6 +370,56 @@ pub trait EpochHandler: StateWriteExt + ConsensusIndexRead {
Ok(reward_queue_entry)
}

async fn process_chain_base_rate(&mut self) -> Result<BaseRateData> {
// We are transitioning to the next epoch, so the "current" base rate in
// the state is now the previous base rate.
let prev_base_rate = self.get_current_base_rate().await?;

tracing::debug!(
"fetching the issuance budget for this epoch from the distributions component"
);
// Fetch the issuance budget for the epoch we are ending.
let issuance_budget_for_epoch = self
.get_staking_token_issuance_for_epoch()
.expect("issuance budget is always set by the distributions component");

// Compute the base reward rate for the upcoming epoch based on the total amount
// of active stake and the issuance budget given to us by the distribution component.
let total_active_stake_previous_epoch = self.total_active_stake().await?;
tracing::debug!(
?total_active_stake_previous_epoch,
?issuance_budget_for_epoch,
"computing base rate for the upcoming epoch"
);

let base_reward_rate =
U128x128::ratio(issuance_budget_for_epoch, total_active_stake_previous_epoch)
.expect("total active stake is nonzero");
let base_reward_rate: Amount = (base_reward_rate * *FP_SCALING_FACTOR)
.expect("base reward rate is around one")
.round_down()
.try_into()
.expect("rounded to an integral value");
tracing::debug!(%base_reward_rate, "base reward rate for the upcoming epoch");

let next_base_rate = prev_base_rate.next_epoch(base_reward_rate);
tracing::debug!(
?prev_base_rate,
?next_base_rate,
?base_reward_rate,
?total_active_stake_previous_epoch,
?issuance_budget_for_epoch,
"calculated base rate for the upcoming epoch"
);

// Set the next base rate as the new "current" base rate.
self.set_base_rate(next_base_rate.clone());
// We cache the previous base rate in the state, so that other components
// can use it in their end-epoch procesisng (e.g. funding for staking rewards).
self.set_prev_base_rate(prev_base_rate);
Ok(next_base_rate)
}

/// Called during `end_epoch`. Will perform state transitions to validators based
/// on changes to voting power that occurred in this epoch.
async fn set_active_and_inactive_validators(&mut self) -> Result<()> {
Expand Down

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