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- Optimistic Rollups (ORs) are one type of layer 2 scaling solution that do not run on Ethereum's base layer but on top of it.
- Contrasting with sidechain solutions, optimistic rollups still use the primary Ethereum chain for consensus and security.
- This enables running smart contracts at scale while still being secured by Ethereum.
- These constructions resemble Plasma, but trade the almost infinite scalability of Plasma to run an EVM compatible Virtual Machine called OVM (Optimistic Virtual Machine) which enables ORs to run anything Ethereum can.
- The name Optimistic Rollups originates from how the solution works.
- 'Optimistic' is used because aggregators publish only the bare minimum information needed with no proofs, assuming the aggregators run without commiting frauds, and only providing proofs in case of fraud.
- 'Rollups' is used because transactions are commited to main chain in bundles (that is, they are rolled-up).
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- Optimistic rollups are a layer 2 scaling solution. The goal of optimistic rollups is to decrease latency — the amount of time it takes to confirm a transaction, currently limited by Ethereum’s block time of about 13 seconds — and increase transaction throughput — the number of transactions that can be processed each second — thereby reducing gas fees.
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Fraud Proofs
- Rollups receives the transaction requests
- The rollups then groups them together and rolls them into the same “paper”
- It executes the papers containing the transactions with their own computation outside Ethereum
- It publishes the outcome on Ethereum, the main chain
Running a version of the EVM off-chain enables developers to deploy the same smart contracts they would deploy on the Ethereum main chain
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- All outcomes that are transmitted to Eth are assumed to be “valid”, which is why “optimistic” is included
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- While being “optimistic”, there could be fraud.
- However, optimistic rollups have a dispute system that can ensure that anybody can challenge a fraudulent or invalid transaction.
- Validators are encouraged to identify fraudulent transactions, prove their fraud, and rewrite them.
- Every 1–2 weeks, anyone can challenge the submitted proof and claim that they’re fraud. As a result, optimistic roll-ups have a long onboarding period in order to ensure that fraud is detected before submitting the batch onto Ethereum.
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- Rollups, broadly, are also sidechains that deploy a novel technical framework in order to scale and process transactions.
- They bundle (called “roll up”) transactions from their chains and send them back to the Ethereum L2 in the bundled state (called a proof, or more accurately a SNARK)— only exposing the most important information.
- Vitalik Buterin is very pro-rollup with his blog post “a rollup centric Ethereum roadmap”.
- Optimistic roll-ups are a type of roll-up that allow for compatibility with the Ethereum Virtual Machine (EVM) — meaning smart contracts deployed on Ethereum can be re-deployed on L2 with relatively minimal additional technical lift.
- They’re called “optimistic” roll-ups because they assume that the proof (i.e., the rolled up batch of transactions) provided for each transaction batch is valid.
- Every 1–2 weeks, anyone can challenge the submitted proof and claim that they’re fraud. As a result, optimistic roll-ups have a long onboarding period in order to ensure that fraud is detected before submitting the batch onto Ethereum.
- Optimism and Arbitrum are the two leading optimistic roll-up solutions — with the former being integrated by two leading dapps: Uniswap and Synthetix.
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- Arbitrum
- Optimism
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