FeeManager Precompile

Activating the Precompile

You can configure the parameters of the dynamic fee algorithm on chain using the FeeManager. In order to activate this feature, you will need to provide the feeManagerConfig configuration in the genesis:

{
  "config": {
    "feeManagerConfig": {
      "blockTimestamp": 0,
      "adminAddresses": ["0x8db97C7cEcE249c2b98bDC0226Cc4C2A57BF52FC"]
    }
  }
}

Interface and Address

The FeeManager precompile is located at address 0x0200000000000000000000000000000000000003 and implements the following interface:

//SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;
 
interface IFeeManager {
  struct FeeConfig {
    uint256 gasLimit;
    uint256 targetBlockRate;
    uint256 minBaseFee;
    uint256 targetGas;
    uint256 baseFeeChangeDenominator;
    uint256 minBlockGasCost;
    uint256 maxBlockGasCost;
    uint256 blockGasCostStep;
  }
  event FeeConfigChanged(address indexed sender, FeeConfig oldFeeConfig, FeeConfig newFeeConfig);
 
  // Set fee config fields to contract storage
  function setFeeConfig(
    uint256 gasLimit,
    uint256 targetBlockRate,
    uint256 minBaseFee,
    uint256 targetGas,
    uint256 baseFeeChangeDenominator,
    uint256 minBlockGasCost,
    uint256 maxBlockGasCost,
    uint256 blockGasCostStep
  ) external;
 
  // Get fee config from the contract storage
  function getFeeConfig()
    external
    view
    returns (
      uint256 gasLimit,
      uint256 targetBlockRate,
      uint256 minBaseFee,
      uint256 targetGas,
      uint256 baseFeeChangeDenominator,
      uint256 minBlockGasCost,
      uint256 maxBlockGasCost,
      uint256 blockGasCostStep
    );
 
  // Get the last block number changed the fee config from the contract storage
  function getFeeConfigLastChangedAt() external view returns (uint256 blockNumber);
 
  // IAllowList
  event RoleSet(uint256 indexed role, address indexed account, address indexed sender, uint256 oldRole);
 
  // Set [addr] to have the admin role over the precompile contract.
  function setAdmin(address addr) external;
 
  // Set [addr] to be enabled on the precompile contract.
  function setEnabled(address addr) external;
 
  // Set [addr] to have the manager role over the precompile contract.
  function setManager(address addr) external;
 
  // Set [addr] to have no role for the precompile contract.
  function setNone(address addr) external;
 
  // Read the status of [addr].
  function readAllowList(address addr) external view returns (uint256 role);
}

The FeeManager precompile uses the AllowList interface to restrict access to its functionality.

In addition to the AllowList interface, the FeeManager adds the following capabilities:

getFeeConfig: retrieves the current dynamic fee config
getFeeConfigLastChangedAt: retrieves the timestamp of the last block where the fee config was updated
setFeeConfig: sets the dynamic fee config on chain. This function can only be called by an Admin, Manager or Enabled address.
FeeConfigChanged: an event that is emitted when the fee config is updated. Topics include the sender, the old fee config, and the new fee config.

You can also get the fee configuration at a block with the eth_feeConfig RPC method. For more information see here.

Implementation

You can find the implementation of the FeeManager precompile in the subnet-evm repository.

Initial Fee Config Configuration

It's possible to enable this precompile with an initial configuration to activate its effect on activation timestamp. This provides a way to define your fee structure to take effect at the activation.

To use the initial configuration, you need to specify the fee config in initialFeeConfig field in your genesis or upgrade file:

{
  "feeManagerConfig": {
    "blockTimestamp": 0,
    "initialFeeConfig": {
      "gasLimit": 20000000,
      "targetBlockRate": 2,
      "minBaseFee": 1000000000,
      "targetGas": 100000000,
      "baseFeeChangeDenominator": 48,
      "minBlockGasCost": 0,
      "maxBlockGasCost": 10000000,
      "blockGasCostStep": 500000
    }
  }
}

This will set the fee config to the values specified in the initialFeeConfig field.

Activating the Precompile

Interface and Address

Implementation

Initial Fee Config Configuration

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