Optimistic Rollups work by assuming all transactions are valid by default and only checking them if challenged, hence "optimistic".
How They Work:
- Transaction Execution: Transactions are executed off-chain by sequencers
- State Commitment: Merkle root of new state is posted to Layer-1
- Challenge Period: 7-day window for anyone to challenge invalid state transitions
- Fraud Proofs: If challenged, the system proves fraud by re-executing transactions on Layer-1
- Slashing: Invalid state transitions result in sequencer penalties
Key Characteristics:
Benefits:
- Near-native EVM compatibility
- Significantly lower gas costs (10-100x reduction)
- Inherits Ethereum's security after the challenge period
- Easy migration for existing dApps
Limitations:
- Withdrawal delays (7-day challenge period)
- Potential for censorship by sequencers
- Requires honest watchers to monitor for fraud
- Higher latency for final settlement
Major Implementations:
- Arbitrum: Uses AVM (Arbitrum Virtual Machine)
- Optimism: Uses OVM (Optimistic Virtual Machine)
- Boba Network: Optimism fork with faster withdrawals
Use Cases:
- DeFi applications requiring EVM compatibility
- Gaming and NFT platforms
- General-purpose dApp deployment
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