📌 Draft Standard

PIP-31: Consumptional Fee Model

Transaction Fee Based on Data Consumption

Authors	Pactus Development Team [info@pactus.org]
Discussion	View Discussion PIP-31
Category	Core
Created	08-08-2024
Requires	PIP-30

Abstract

This document proposes calculating the validator fee based on the amount of data each account consumes daily. It also defines the “Account Creation Fee” as a network fee that each account must pay to the network upon sending its first transaction.

Specification

The transaction fee can be determined based on either the Consumption Fee or the Account Creation Fee. Validators can drop transactions with lower fees, but transactions with higher fees are accepted and kept in the transaction pool.

Consumptional Fee

Each validator can independently calculate the fee for each transaction based on the following formula:

\[\text{fee} = \text{fixed_fee} + ( \text{coefficient} \times \text{consumption} \times \text{unit_price} )\]

Let’s explain the parameters:

Fixed Fee

The fixed_fee is a constant fee applied to each transaction, regardless of its size. This parameter would be part of the node configuration, allowing each validator to set their preferred value. The default value for fixed_fee is proposed to be set to zero.

Consumption

To understand the Consumptional Fee Model, we first need to define consumption.

Transactions are sequences of bytes that are decoded, processed, and stored by validators. Consumption is defined as the number of bytes stored over the last 8640 blocks ¹ for a specific account.

Coefficient

The coefficient is a unitless number that starts at zero and grows exponentially: $0, 1, 2, 4, 8, \dots $

The coefficient would be calculated as follows:

\[n = \frac{\text{consumption}}{\text{daily_limit}}\] \[\displaylines{\text{coefficient} = \begin{cases} 0 & \text{if } n = 0 \\ 2^{n-1} & \text{if } n \geq 1 \end{cases} }\]

In this model, the daily_limit is the number of bytes an account can send each day without paying a fee. This parameter would be part of the node configuration, allowing each validator to set their preferred value.

The default value for daily_limit is proposed to be set at 300 bytes?

Unit Price

The unit_price would define the fee per byte in PAC. This parameter would be part of the node configuration, allowing each validator to set their preferred value.

The default value for unit_price is proposed to be set at 0.01 PAC?

Account Creation Fee

The Consumptional Fee Model could potentially allow attackers to send spam transactions. Since the fee for initial transactions may be minimal or free, an attacker could send transactions to non-existing accounts, which could then send transactions from those accounts to other new accounts, continuing the spam.

To address this, the Account Creation Fee proposes. This fee would be paid only the first time an account initiates a transaction and should be set sufficiently high to deter such attacks. Additionally, the balance of a new account must be at least equal to the account creation fee. This fee is defined as part of the consensus parameters and is not configurable. It is proposed to be set at 1? PAC.

Implementation Considerations

There are some challenges in implementing the Consumptional Fee Model:

Calculating Consumption

To calculate consumption, we can define a map that associates an address with the total size of transactions stored in the blockchain over the last 8640 blocks. When a new block is committed, we update this map by iterating over all transactions in the block and increasing the value for each address by the size of its transactions. Simultaneously, the block from 8640 blocks ago would be retrieved, and the value for each address would be decreased by the size of its transactions.

New Account Detection

To determine if an account is new and hasn’t sent any transactions yet, we can check if its public key is indexed. If the public key is not indexed, it indicates that the account is sending a transaction for the first time, and the account creation fee should be applied.

Withdraw fee

Withdrawal transactions are issued and signed by validators, and the fee for them can be calculated based on the Consumptional Fee model.

References

Copyright

Copyright and related rights waived via CC0.