How gas works
Instead of assigning a fixed gas cost in each instruction, the Filecoin EVM runtime charges FIL gas based on the WASM code execution of the Filecoin EVM runtime interpreter.
Last updated
Was this helpful?
Instead of assigning a fixed gas cost in each instruction, the Filecoin EVM runtime charges FIL gas based on the WASM code execution of the Filecoin EVM runtime interpreter.
Last updated
Was this helpful?
When executing a message that invokes an EVM contract, the Filecoin virtual machine charges for the message chain inclusion (when the message originates off-chain) and then invokes the actor that hosts the contract. The actor is an instance of the EVM actor, which uses the Filecoin EVM runtime interpreter to execute the contract.
The FEVM interpreter must first load its state, including the contract state, which costs additional gas. The interpreter then begins the execution of the contract bytecode. Each opcode interpreted may perform computation, syscalls, state i/o, and send new messages, all of which are charged with FIL gas. Finally, if the contract state is modified, the interpreter must flush it to the blockstore, which costs additional gas.
Generally, it is not possible to compute gas costs for a contract invocation without using gas estimation through speculative execution.
The total gas fee of a message is calculated as the following:
Take a look at the for more information on the various gas-related parameters attached to each message.
Let’s take a transaction as an example. Our gas parameters are:
GasUsage = 1000 attoFIL
BaseFee = 20 attoFIL
Gas limit = 2000 attoFIL
Gas premium = 5 attoFIL
The total fee is (GasUsage × BaseFee) + (Gaslimit x GasPremium):
Additionally, the message sender can also set the GasFeeCap parameter they are willing to pay. If the sender sets the GasLimit too high, the network will compute the amount of gas to be refunded and the amount of gas to be burned as OverEstimationBurn.
Filecoin nodes, such as Lotus, have several JSON-API API endpoints designed to help developers estimate gas usage. The available JSON-RPC APIs are:
GasEstimateMessageGas: estimate gas values for a message without any gas fields set, including GasLimit, GasPremium, and GasFeeCap. Returns a message object with those gas fields set.
GasEstimateGasLimit takes the input message and estimates the GasLimit based on the execution cost as well as a transaction multiplier.
GasEstimateGasPremium: estimates what GasPremium price you should set to ensure a message will be included in N epochs. The smaller N is the larger GasPremium is likely to be.
GasEstimateFeeCap: estimate the GasFeeCap according to BaseFee in the parent blocks.
Gas estimation varies from network to network. For example, the BaseFee on mainnet is different from the BaseFee on the Calibration testnet.
If you’d rather not calculate and estimate gas for every message, you can just leave the optional fields unset. The gas fields will be estimated and set when the message is pushed to the mempool.
Since Filecoin is fully EVM-compatible, Filecoin nodes also provide Ethereum-compatible APIs to support gas estimation:
To request the current max priority fee in the network, you can send a request to a public Filecoin endpoint:
This will output something like:
You can convert the result field from hexadecimal to base 10 in your terminal. Take the result output and remove the 0x from the start. Then use echo to output the conversion:
Gas Filecoin improvement proposals (FIPs):
If you want to learn more about how to use those JSON-RPC APIs for the Filecoin gas model, please check the .
: generates and returns an estimate of how much gas is necessary to allow the transaction to complete.
: returns a fee per gas that is an estimate of how much you can pay as a priority fee, or “tip”, to get a transaction included in the current block.