Gas Price Oracle
This service is responsible for updating the gasPrice in the OVM_GasPriceOracle.sol contract, so the Sequencer can fetch the latest gasPrice and update the L2 gas over time.

Configuration

All configuration is done via environment variables. See all variables at .env.example; copy into a .env file before running.
Environment Variables
Description
Default
L1_NODE_WEB3_URL
The endpoint of Layer 1
L2_NODE_WEB3_URL
The endpoint of Layer 2
DEPLOYER_PRIVATE_KEY
The owner of OVM_GasPriceOracle
SEQUENCER_PRIVATE_KEY
The private key of sequencer account
PROPOSER_PRIVATE_KEY
The private key of proposer account
RELAYER_PRIVATE_KEY
The private key of relayer account
FAST_RELAYER_PRIVATE_KEY
The private key of fast relayer account
GAS_PRICE_ORACLE_ADDRESS
The address of OVM_GasPriceOracle
GAS_PRICE_ORACLE_FLOOR_PRICE
The minimum L2 gas price
150000
GAS_PRICE_ORACLE_ROOF_PRICE
The maximum L2 gas price
20000000
GAS_PRICE_ORACLE_MIN_PERCENT_CHANGE
The gas price will be updated if it exceeds the minimum price percent change.
0.1
POLLING_INTERVAL
The polling interval
10 * 60 * 1000

Building & Running

  1. 1.
    Make sure dependencies are installed - run yarn in the base directory
  2. 2.
    Build yarn build
  3. 3.
    Run yarn start

L2 Gas Fee

The L2 gas fee is
gasFee = gasPrice * gasLimit
GAS PRICE The gas price is fixed and is equal to 1 GWei. Notably, the way fees are calculated on L2 differ from what you might be used to on L1, where the gas price can be adjusted e.g. to ensure faster mining. Since there is no mining on L2, the gas price is fixed.
GAS LIMIT On L2, we vary the gas limit to accommodate the ever-changing costs of running the L2. This can be confusing, since on L1, the gas limits are constants that depend only on the type of transaction - e.g. on L1, a standard ETH transfer requires a gas limit of 21,000 units of gas.
GAS LIMIT SETTINGS You could use the maximum gas limit. The estimated gas limit is based on rollup_gasPrices, which is composed of L1SecurityFee and L2GasPrice based on the following expression:
estimatedGasLimit = L1SecurityFee / L2GasPrice + L2EstimatedExecutionGasLimit
The L1SecurityFee changes gradually to reflect our service cost, primarily, the cost of writing state roots into L1, and the significant cost of relaying messages from L1 to L2 (e.g. deposits) and back from L2 to L1 (e.g. exits). Unlike other L2's, we include the cost of relaying messages in our gas limits, so you do not have to pay two different fees or have to worry about relaying your messages.

L1 Security Fee

The L1 security fee is for the cost of submitting the state roots and tx roots to L1. It's calculated via
L1BasePrice * scalar * (overhead + dataLength)
The overhead is the x% percentage of the average gas usage of the L1 txs that submitting the state and tx roots within last 1000 blocks. We adjust x based on our operation cost.