What is a Rollup?
A rollup is a scaling approach that executes transactions off the main chain and links the results and necessary validation data back to the main network.
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What does a rollup do?
A rollup is a scaling approach that executes transactions off the main chain and sends the results, along with the data or proofs required for verification, to the main network. The goal is to process more transactions at a lower cost by using the limited space on the main chain more efficiently. Many Layer 2 solutions in the Ethereum ecosystem utilize this approach.
You can think of it as collecting a group of transactions under a single common record. Users see fast results in the application; later, the batch of transactions is linked to the main chain. However, a rollup is not merely a file compression method. How incorrect results are rejected and how user assets are protected are fundamental parts of the design.
Two fundamental approaches
Optimistic rollups rely on the ability to challenge proposed results through specific processes. In rollups that use validity proofs, a cryptographic proof demonstrates that the computation was performed correctly. This second group is frequently referred to as ZK-rollups. These names alone do not explain all the security differences between various implementations.
Where the data is published, who can update the software, what happens if the sequencer stops, and the exit mechanism are also critical. Even if two networks fall into the same category, these details may differ.
An important difference for the user
Transferring assets to a rollup network usually requires a bridging transaction. Although the same address may appear in your wallet, the balances on the main chain and the rollup are separate. Assets sent on the wrong network might not be supported by the receiving platform.
Furthermore, the transfer that appears fast in the application is not the same as the exit time to the main chain. Official bridges may have waiting periods; fast exit services may add different fees and counterparty risks. Before using a rollup, learn not just the transaction fee, but also how to withdraw your assets when necessary.