pub struct TargetedFeeAdjustment<T, S, V, M, X>(_);
Expand description

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.

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

Make conversion.
Minimum multiplier. Any outcome of the convert function should be at least this.
Maximum multiplier. Any outcome of the convert function should be less or equal this.
Target block saturation level
Variability factor

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