Analysis of Ethereum Scalability Solutions: Optimistic Rollups and ZK-Rollups

Ethereum, as one of the most active blockchain platforms today, supports numerous decentralized applications, from DeFi to NFTs, and its ecosystem is thriving. However, the booming on-chain transactions also bring some inherent challenges, such as skyrocketing transaction fees due to network congestion, extended processing times, and increased failure rates, which seriously affect participants' enthusiasm.

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

Currently, 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 raw transaction data to the mainnet. When submitting, L2 nodes assume by default that these transactions are valid, which greatly enhances the speed and efficiency of transaction confirmations.

If a validator discovers a problematic transaction, they can submit a fraud proof within seven days. The smart contract on L1 will validate this proof. If a problematic transaction is indeed found, the batch containing the transaction and subsequent batches will be rolled back, the malicious node will be punished, and the validator will receive a reward.

If no fraud proof is received within seven days, all transactions will be confirmed as legitimate. The existence of the "fraud proof" mechanism itself serves as an effective deterrent, and in practice, very few nodes submit fraud proofs or are confirmed to have acted maliciously.

The main drawbacks of Optimistic Rollups are the liquidity issues that may arise from the seven-day challenge period, as well as the potential centralization risks.

ZK-Rollups

Unlike Optimistic Rollups, ZK-Rollups require a validity proof to be included along with the compressed data when submitting data to the chain. This means that although ZK-Rollups also conduct transactions off-chain, a validity proof must be calculated off-chain before the official submission.

ZK technology existed before the emergence of blockchain, but its application was limited by the complexities of the real world. The advantage of blockchain applications using ZK technology is that it can confine complexity within smart contracts, only requiring the verification of on-chain data and computations, without relying on any centralized organization or individual.

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

Layer2 Cost Analysis

The costs of Optimistic Rollups mainly include: the fees for submitting compressed transaction data to L1 and the operating costs of L2 nodes. The good news is that Ethereum's EIP-4844 proposal has significantly reduced the costs of interaction between L2 and the mainnet. However, maintaining nodes requires locking up a large amount of funds, which may cause investors to miss out on other opportunities.

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

Summary

Optimistic Rollups and ZK-Rollups are both key solutions for the Ethereum ecosystem to address scalability challenges. With the implementation of upgrades such as Ethereum EIP-4844, the data publication costs for L2 have been significantly reduced, which will further unlock the potential of both solutions and promote the continued development of the Ethereum ecosystem.