A change in fee computation to deal with storage congestion.

Introduce a hidden Storage Base Fee based on previous blocks storage growth and that is applied to the gas base fee.

Moonbeam chain state needs to be sustainable for collators and archive nodes. With its current fee mechanism, it doesn't account sufficiently for new storage data being added.

In order to reduce the impact on the gas price, an additional mechanism is proposed.

A new storageBaseFee is included and increased/decreased based on previous block state increase and a given threshold.

The notion of baseFee is split into 2:

• gasBaseFee (hidden to the user) which represents the price per gas executed.
• baseFee (visible to the user) which represents the total price paid per gas consumed and includes the storage base fee into consideration.

A transaction with not enough gasPrice to compensate for the gas and storage will revert with gasPrice too low.

The storage base fee is the cost of storing 1 byte of data in the chain state. One straightforward approach to dynamically adjusting this would be to use the same formula used in Substrate's pallet-transaction-payment which has been developed to achieve long-term average targets. Moonbeam uses this for its base-fee implementation based on block weight, but it would be useful here as well.

Since the goal for storage is very long-term growth targets as opposed to short term congestion relief in the case of the base-fee, different parameters could be used to smooth it out:

given:
    s = previous block growth (cannot be negative)
    s' = ideal block growth = 5_000
    m = max block growth = 50_000
        diff = (s - s') / m
        v = 0.00001
        t1 = (v * diff)
        t2 = (v * diff)^2 / 2
    then:
    next_multiplier = prev_multiplier * (1 + t1 + t2)

The gasBaseFee is the same as the baseFee defined before this MBIP. It simply represents the cost of executing 1 gas.

Before this EIP, to compute the cost of a transaction (without tips), the [EIP-1559] used gasUsed * baseFee with the baseFee being the same for each transaction of a block.

Using this EIP, the cost of the transaction is:

  txCost = (gasUsed * gasBaseFee) + (byteStored * storageBaseFee)

To guarantee the user is not paying more than the gasPrice (or EIP-1559 equivalent) multiplied by the gasLimit, we need to ensure the gasPrice will cover the gas baseFee and also the storageBaseFee.

The gas being limited to 15_000_000 gas and the storage soft limit to 50_000 bytes, the final baseFee needs to be proportionally adapted to each value (otherwise the baseFee would be very high and would impact the user perception of the price paid)

blockStorageSoftLimit = 50_000 bytes
blockGasLimit = 15_000_000 gas
baseFee = gasBaseFee + (storageBaseFee * blockStorageSoftLimit / blockGasLimit)

/!\ A transaction requiring proportionally more storage than the provided gasLimit will require to provide a higher gasPrice than the suggested baseFee.
The blockStorageSoftLimit is a soft limit, but a transaction could go over that limit if it pays the correct gasPrice.

A minimum storage fee of 0.0005 GLMR / Byte would lead to:
1GB => 1_000_000_000 * 0.0005 GLMR => 500_000 GLMR

A storageBlockExpectation of 50_000 bytes would be equivalent to:

Using:

• gasBaseFee: 200 Gwei
• storageBaseFee: 500_000 Gwei (per byte)

The RPC would return a baseFee of 200 + (500_000 / 15_000_000 * 50_000) => 1_866 Gwei

Performing a transaction that uses 340_000 gas and increase the storage by 180 bytes would cost: 200 * 340_000 + 500_000 * 180 => 0.158 GLMR

By providing a baseFee of 1,866 Gwei in this example, the user is expected to pay 1_866 * 340_000 => 0.634 GLMR and will pay 0.158 GLMR.

A transaction with a gasLimit of 100,000 and using 500 bytes of storage would fail with a gasPrice == baseFee. User is expecting to pay: gasLimit (100_000) * 1_866 Gwei (baseFee) => 0.186 GLMR However the real cost of the transaction is: gasUsed(100_000) * gasBaseFee (200) + storageUsed (500 bytes) * storageBaseFee (500_000) => 0.270 GLMR

The user would have to provide a higher gasPrice (>= 2_700 Gwei) in order to get the transaction included.

This EIP increases the displayed baseFee to the users, which might give a false impression of a higher price to pay.

It also break the assumption that: paid fee == gas used * gas price (or paid fee == gas used * base fee for EIP-1559)

In the case of a transaction with a lot of storage increase, this will report gasPrice too low even if the gasPrice provided is over the baseFee. This would require to manually increase the gasPrice.