Ethereum L2 Scaling Battle: A Comparative Analysis of Optimistic and ZK-Rollups

Ethereum, as one of the most active platforms in the current blockchain field, hosts a large number of decentralized applications, from Decentralized Finance to NFT, and the ecosystem is thriving. However, the prosperity of on-chain transactions also brings some inherent challenges, such as high transaction fees caused by network congestion, extended transaction times, and increased failure rates, which severely affect user participation enthusiasm.

To address these issues and maintain the distributed characteristics of the main chain, the community primarily adopted L2 scaling solutions. The core principle of L2 is to transfer computation and transactions from the main network (L1) to a second layer network for execution, only submitting the final transaction results to the main network. This approach not only improves transaction efficiency and reduces costs but also preserves the security of the main network.

Currently, the more well-known L2 solutions include Rollups and sidechains. Rollups can be further divided into Optimistic Rollups and Zero-Knowledge Rollups (ZK-Rollups).

Optimistic Rollups

Optimistic Rollups perform all transaction computations and state updates on the L2 network, and then batch publish the compressed original data of the transactions to the mainnet. L2 nodes assume these transactions are valid by default unless someone challenges them. This approach greatly improves transaction confirmation speed and efficiency.

After the transaction is submitted, validators have seven days to submit fraud proofs. If a problematic transaction is found, the related batch and its subsequent batches will be rolled back, the malicious nodes will be punished, and the validators will receive rewards. If no fraud proof is received within seven days, all transactions will be confirmed as legitimate.

The existence of the "Proof of Fraud" mechanism itself has a strong deterrent effect, and in reality, very few nodes submit proof of fraud or are proven to have acted maliciously. The reasons for this situation include that the project itself has been thoroughly tested, the cost of malicious acts is high, and the potential economic and reputational losses far exceed the negligible gains that could be obtained.

In fact, interruptions caused by network fluctuations and software bugs are more common than malicious behavior by nodes. The main drawback of Optimistic Rollups is the liquidity issues and potential centralization risks brought about by the seven-day challenge period.

ZK-Rollups

Unlike Optimistic Rollups, ZK-Rollups require an validity proof to be submitted along with the compressed data when submitting data on-chain. This means that ZK-Rollups conduct transactions off-chain and calculate the validity proof before officially submitting it.

The concept of ZK technology predates the emergence of blockchain, but its application scenarios are limited by the complexity of the real world. The advantage of blockchain applications using ZK technology is that it can confine complexity within smart contracts, requiring only the verification of on-chain data and computations, without relying on centralized organizations or individuals.

The complexity of ZK-Rollups lies in the need to compile the transaction execution data and logic into complex logical circuit diagrams, and then use a specialized prover to generate quickly verifiable results through cryptographic calculations. This process typically requires powerful computing capabilities and specialized compilers and verifiers.

Layer2 cost

L2 networks aim to reduce user interaction costs on L1, but they also have their own costs.

The costs of Optimistic Rollups mainly come from two aspects: the transaction fees when submitting the compressed transaction data to L1, and the operating costs of L2 nodes. These costs will ultimately be passed on to users. The good news is that Ethereum's EIP-4844 proposal significantly reduces the costs of interaction between L2 and the mainnet. Additionally, maintaining nodes requires locking up a large amount of capital, which may lead investors to miss out on other opportunities.

The main cost of ZK-Rollups comes from computational resources, as generating zero-knowledge proofs requires a large amount of computational resources and specialized hardware. Like Optimistic Rollups, it also incurs transaction fees for submitting data to the chain. Additionally, the demand for specialized hardware may lead to greater centralization of the network.

Summary

Optimistic Rollups and ZK-Rollups are key solutions for the Ethereum ecosystem to address scalability challenges. With the implementation of upgrades like Ethereum EIP-4844, the cost of data publishing on L2 has been significantly reduced, which will further unleash the potential of both solutions and drive the continued development and innovation of the Ethereum ecosystem.