Arbitrum Rollup is an off-chain protocol managed by on-chain Ethereum contracts, developed by Offchain Labs. It is a Layer 2 scaling solution designed to enhance Ethereum's throughput, reduce costs for smart contract deployment and operation, and maintain trustless security.
How Arbitrum Rollup Works
Rollup technology aims to record all transaction data on the main chain. Its core idea is to aggregate and compress a large number of transactions into a single transaction published to the main chain. The actual computation and storage of contracts occur off-chain, reducing the operational and storage burden on the main chain and enabling high network throughput.
Key Features of Arbitrum
- Trustless Security: Rooted in Ethereum's security, any party can ensure correct Layer 2 outcomes.
- Ethereum Compatibility: Supports unmodified EVM contracts and Ethereum transactions.
- Scalability: Moves contract computation and storage off the main Ethereum chain, allowing higher throughput.
- Low Cost: Minimizes the system's L1 gas footprint, reducing per-transaction costs significantly.
Transaction Lifecycle in Arbitrum
A transaction goes through several stages before being confirmed:
- Sequencing: The sequencer orders and confirms the transaction but hasn't yet published it to the L1 chain. At this stage, the transaction can be considered final if the user trusts the sequencer.
- Batch Publication: The sequencer publishes a batch containing the transaction to the L1 chain. The sequencer no longer needs to be trusted once the batch is confirmed on L1.
- Assertion Creation: Validators create assertions about the transaction results. Other validators can stake on these assertions.
- Challenge Period: A 7-day challenge period ensures the assertion is confirmed, locking the transaction results on the L1 chain.
ArbGas and Fees
ArbGas measures computational costs on the Arbitrum chain, similar to Ethereum gas. However, Arbitrum lacks a hard ArbGas limit, and ArbGas is consumed faster than Ethereum gas. Fees are charged in ETH and cover L2 transactions, L1 data calls, computation, and storage costs.
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Throughput and Performance
Since all Arbitrum transaction data is published to Ethereum, the cost per transaction and the number of transactions per second are limited by Ethereum's data publishing capacity. Optimizing transaction compression is crucial for reducing costs and improving throughput. For simple transfers without call data, Arbitrum can handle up to 4,500 transactions per second.
Cross-Contract Communication
Calls from Ethereum to Arbitrum are fast, while calls from Arbitrum to Ethereum are slower due to the challenge period. However, elegant solutions exist for quickly transferring assets from Arbitrum to Ethereum.
Arbitrum Virtual Machine (AVM)
Although Arbitrum supports the EVM, it operates on the Arbitrum Virtual Machine (AVM)底层. The AVM is never exposed to developers or users. It shares many aspects with the EVM but differs in areas necessitated by Layer 2 protocol requirements and multi-round challenge protocols for dispute resolution.
Staking and Validation
Anyone can become a validator or staker in the Arbitrum protocol. Stakers deposit ETH as collateral, which they can reclaim if they are not found cheating. These roles are permissionless, ensuring decentralization.
ArbOS: The Operating System
ArbOS is a trusted "operating system" on Layer 2 that isolates untrusted contracts, tracks resource usage with ArbGas, and manages the economic model for funding chain operations. It translates EVM code into equivalent AVM code for execution.
L1 and L2 Interaction Differences
- L1 to L2 Deposits: Take approximately 10 minutes.
- L2 to L1 Withdrawals: Require 8 days for security reasons, allowing validators time to detect and prove fraud.
- L2 to L2 Transfers: Occur almost instantly.
Transferring Assets from L1 to L2
There are two primary methods for moving assets from Ethereum to Arbitrum:
- Official Arbitrum Bridge: Use the Arbitrum Bridge for both testnet and mainnet transfers.
- Third-Party Bridges: Services like cBridge and Multichain also support cross-chain transfers, though testnet support may vary.
Development Considerations and Pitfalls
Developers familiar with Ethereum will find Arbitrum's tools and protocols familiar but should be aware of several key differences:
- EVM/Solidity Behavior: Some operations behave differently on Arbitrum. Consult the Solidity Support documentation for details.
- Timing Assumptions: Assumptions about
block.timestampandblock.numberfrom L1 do not hold on Arbitrum. Rely onblock.timestampfor larger timeframes. - L1-to-L2 Transactions: Be cautious with "retryable tickets" and address aliasing. Ensure adequate payment for base submission fees to avoid failures.
- Hardcoded Gas Values: Adjust or remove hardcoded gas values, as ArbGas differs from Ethereum gas.
- ETH Deposits: Understand the special handling of ETH deposits via retryable tickets.
- Randomness: Do not rely on L2 block hashes for randomness.
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Frequently Asked Questions
What is Arbitrum Rollup?
Arbitrum Rollup is a Layer 2 scaling solution for Ethereum that improves throughput and reduces costs while maintaining security and compatibility with existing Ethereum tools.
How does Arbitrum ensure security?
Arbitrum leverages Ethereum's security model, allowing any honest validator to enforce correct outcomes. A challenge period provides time for fraud detection and resolution.
Can I use existing Ethereum tools with Arbitrum?
Yes, Arbitrum fully supports the EVM, meaning all standard Ethereum frontend tools and smart contract languages work without modification.
Why do L2 to L1 withdrawals take 8 days?
The 8-day challenge period ensures validators have enough time to synchronize with the chain and dispute fraudulent transactions if necessary.
What is ArbGas?
ArbGas is a unit for measuring computational cost on Arbitrum, similar to Ethereum gas but consumed faster and without a hard limit.
How do I transfer assets from Ethereum to Arbitrum?
You can use the official Arbitrum Bridge or third-party bridges like cBridge and Multichain. The process typically takes about 10 minutes for deposits.
Conclusion
Arbitrum Rollup offers a powerful combination of security, compatibility, scalability, and low cost for Ethereum developers and users. By understanding its transaction lifecycle, fee structure, and development considerations, you can leverage Arbitrum to build efficient and secure decentralized applications.