What is Rollup?

Rollup can be translated as "packaging" and is a second-layer solution.

In a simple analogy, if we imagine the blockchain as a ledger, without Rollup, each completed transaction requires writing a record in the ledger, which can be laborious and expensive. With Rollup, multiple transactions can be recorded outside the ledger first, and the summarized results are then packaged and written into the ledger. This process reduces the burden on the main blockchain, increasing processing speed and efficiency.

In Ethereum's history, Rollup technology is mainly divided into two categories: Optimistic Rollup (OP-Rollup) and Zero Knowledge Rollup (ZK-Rollup).

• Optimistic Rollup (Optimistic Rollup) assumes all transactions are valid, allowing them to be bundled first. Only when evidence proving these transactions are invalid (fraud proofs) appears within a certain period, corresponding actions are taken. On Ethereum, representative projects of Optimistic Rollup include Optimism and Arbitrum.
• Zero Knowledge Rollup (Zero Knowledge Rollup) adopts a "pessimistic" approach, using zero-knowledge proof technology to verify transaction validity. It first proves that these transactions are sound and then transmits the data to the main chain. On Ethereum, representative projects using this technology include zkSync and Starknet.

A new concept has emerged, namely Sovereign Rollup. Unlike the previous Ethereum rollups, Sovereign Rollup emphasizes independent sovereignty, not relying on the Layer 1 (L1) settlement layer, forming a self-governing blockchain system. The rise of the modular blockchain project Celestia has gained widespread attention, making people realize that it is possible to build Rollup chains with sovereignty and self-management without depending on L1 settlement.