The Tech Journey: Lower Gas Costs & Storage Layer on Metis

9 min readApr 12, 2022

Why are transaction costs not in cents yet?

Much of the gas cost incurred on an optimistic layer 2 network is to offset the cost to rollup the transaction to ethereum L1. Ethereum mainnet is expensive. For example,

The above transaction rolled up 107 transactions. At the time of writing this post, the cost of that transaction is $100 dollars. If we factor in the transaction cost for submitting the state batch, the cost of each transaction is already above a dollar. And this is when the gas price is ONLY at 75 GWEI. Ethereum mainnet when busy can have gas price up to 200 GWEI (or more when large airdrops are happening) The roll-up cost of each transaction can easily surpass 3 dollars, making layer 2 transactions cost still a bit steep for many users.

At this point, someone may ask: so if the majority of the cost comes from the transaction rollup, why do we rollup that expensive blob of data?

Why do we need to roll-up the transaction data?

The answer is network security. Transaction data is crucial to ensure data integrity of an optimistic layer 2 network. When Metis produces a block, there is no block production consensus. The block is made by the current block producer on duty. Metis’s security is ensured by a delayed validation consensus, i.e. validators constantly checking that the block producer and the sequencer both are honest and challenging when fraudulent behavior is observed.

Metis’s validation consensus is accomplished by two separate mechanisms. The first mechanism ensures the block production correctness in near real time. Basically, when a block is produced by the current block producer on duty, the peer network will immediately validate the block. If the block producer on duty is dishonest, the peers will catch it immediately on the first block and halt the network. The election of a new block producer will follow with a rollback of one block. The peer network holds the block producer accountable and minimizes the rollback required. However, this mechanism does not prevent sequencers to submit incorrect state…