name type size description
rootProducer address 20 Address of root producer.
merkleTreeRoot bytes32 32 Claimed Merkle root of list of transactions.
commitmentHash bytes32 32 Simple hash of list of transactions.
rootLength uint256 32 Number of roots.
feeToken uint256 32 Token ID of all fees paid in this root.
fee uint256 32 Feerate of all fees paid in this root.

Each root header commits to a list of transactions. Each root is a root header and a list of transactions (and does not exist as a canonical data structure). Blocks contain one or more root header hashes (i.e. hashes of root headers), and so implicitly commit to a list of transactions. For more information of why multiple roots are used instead of the more traditional single-transactions-root, see Block Architecture.

When committing a new root to the contract, the root header minus the commitmentHash is provided, along with a list of transactions. The commitmentHash is then computed by simply hashing the list of transactions. This means that root headers claim a Merkle root of their transactions, which is assumed to be correct optimistically to save gas. If the claimed Merkle root is incorrect, a fraud proof can be constructed to show this.

The maximum size in bytes of the list of transactions in a single root is the MAX_ROOT_SIZE parameter (57600). This limit is placed to ensure that the transactions can always be Merkleized within the gas limit of a single Ethereum block in a fraud proof.

The maximum number of transactions in a single root is the MAX_TRANSACTIONS_IN_ROOT parameter (2048).