Struct pallet_transaction_payment::TargetedFeeAdjustment

pub struct TargetedFeeAdjustment<T, S, V, M, X>(/* private fields */);

A struct to update the weight multiplier per block. It implements Convert<Multiplier, Multiplier>, meaning that it can convert the previous multiplier to the next one. This should be called on on_finalize of a block, prior to potentially cleaning the weight data from the system pallet.

given: s = previous block weight s’= ideal block weight m = maximum block weight diff = (s - s’)/m v = 0.00001 t1 = (v * diff) t2 = (v * diff)^2 / 2 then: next_multiplier = prev_multiplier * (1 + t1 + t2)

Where (s', v) must be given as the Get implementation of the T generic type. Moreover, M must provide the minimum allowed value for the multiplier. Note that a runtime should ensure with tests that the combination of this M and V is not such that the multiplier can drop to zero and never recover.

Note that s' is interpreted as a portion in the normal transaction capacity of the block. For example, given s' == 0.25 and AvailableBlockRatio = 0.75, then the target fullness is 0.25 of the normal capacity and 0.1875 of the entire block.

Since block weight is multi-dimension, we use the scarcer resource, referred as limiting dimension, for calculation of fees. We determine the limiting dimension by comparing the dimensions using the ratio of dimension_value / max_dimension_value and selecting the largest ratio. For instance, if a block is 30% full based on ref_time and 25% full based on proof_size, we identify ref_time as the limiting dimension, indicating that the block is 30% full.

This implementation implies the bound:

• v ≤ p / k * (s − s')
• or, solving for p: p >= v * k * (s - s')

where p is the amount of change over k blocks.

Hence:

• in a fully congested chain: p >= v * k * (1 - s').
• in an empty chain: p >= v * k * (-s').

For example, when all blocks are full and there are 28800 blocks per day (default in substrate-node) and v == 0.00001, s’ == 0.1875, we’d have:

p >= 0.00001 * 28800 * 0.8125 p >= 0.234

Meaning that fees can change by around ~23% per day, given extreme congestion.

More info can be found at: https://research.web3.foundation/en/latest/polkadot/overview/2-token-economics.html

Trait Implementations

impl<T, S, V, M, X> Convert<FixedU128, FixedU128> for TargetedFeeAdjustment<T, S, V, M, X>

where T: Config, S: Get<Perquintill>, V: Get<Multiplier>, M: Get<Multiplier>, X: Get<Multiplier>,

fn convert(previous: Multiplier) -> Multiplier

Make conversion.

impl<T, S, V, M, X> MultiplierUpdate for TargetedFeeAdjustment<T, S, V, M, X>

where T: Config, S: Get<Perquintill>, V: Get<Multiplier>, M: Get<Multiplier>, X: Get<Multiplier>,

fn min() -> Multiplier

Minimum multiplier. Any outcome of the convert function should be at least this.

fn max() -> Multiplier

Maximum multiplier. Any outcome of the convert function should be less or equal this.

fn target() -> Perquintill

Target block saturation level

fn variability() -> Multiplier

Variability factor