Optimistic Rollup has been widely recognized, Fuel Labs, Offchain Labs, Optimism and Hubble are all building Optimistic Rollup infrastructure.
Recommended reading: ” How does the Ethereum Layer 2 ecosystem stand? 》
Original title: “Introduction | Optimistic Rollup Minimalist Interpretation”
Written by: John Adler
Translation & Proofreading: Min Min & A Jian
Today, for Ethereum and all blockchains, Optimistic Rollup is the most promising scalability solution. But what is Optimistic Rollup (ORU)? Why does it make Ethereum developers and scalability researchers so excited?
In this article, we will introduce the basic knowledge of ORU in an easy-to-understand way. If you want to know the in-depth technical details, please check this article ( Chinese translation ).
Features
ORU has many desirable characteristics. Among all blockchain scalability technologies, its characteristics are unparalleled. A reasonably designed ORU system will have the following characteristics:
- Trust-free . Unlike traditional sidechain technology, ORU is trust-free (or in a more professional way, it has the feature of minimizing trust). You can withdraw your funds from Rollup at any time, without trusting that most block producers on ORU are honest.
- License-free . Unlike Plasma, ORU is license-free. Anyone can become a block producer on ORU, because all block data on Rollup is published on Ethereum and can be obtained from Ethereum. How to choose the next leader is a specific implementation issues, rather than a fundamental limitation.
- Free hosting . As mentioned above, because ORU is both trust-free and permission-free, you can withdraw your funds at any time, and no one can stop you. Therefore, ORU is free of hosting.
- Strong expressiveness . Unlike ZK Rollup, ORU (in terms of theory and practice) is highly expressive. Whether it is a Bitcoin-like UTXO payment or a mature and compatible EVM execution, ORU can handle it.
- Open to participation . Unlike payment channels, ORU supports smart contracts and is open to everyone like Uniswap.
- High capital efficiency . Unlike payment channels, ORU does not require users to lock funds in advance.
- Anti-chain congestion . Unlike payment channels and Plasma, ORU can withstand congestion on the chain because ORU’s fraud proof is at the block level, not a closing mechanism like payment channels or an exit mechanism like Plasma.
- No need for new cryptography . Unlike ZK Rollup, ORU does not require any new cryptography.
- Fast (not instant) finality . Unlike ZK Rollup, ORU does not need to generate a proof, so ORU blocks can be immediately published to Ethereum. Since valid ORU blocks cannot be rolled back, once these blocks are published on Ethereum, they can obtain the same finality as Ethereum.
A brief history of Optimistic Rollup
One of the earliest measures to enhance Bitcoin’s scalability was the side chain. The side chain is a blockchain that runs together with the parent chain, but has different characteristics: shorter block time, larger block size, and more expressive smart contracts. However, ordinary side chains have a fatal disadvantage: if most miners/validators on a side chain are dishonest, user funds will be stolen.
Over the years, many technologies have been trying to enhance the security of side chains to ensure that user funds will not be stolen even if the vast majority of participants are dishonest (this is called two-way anchoring of trust minimization) . Earlier examples include merged mining, shadow chain, and then Plasma and ZK Rollup. Interestingly, before the advent of ORU, a similar solution was delayed state execution under the sharding mechanism (we will talk about this soon!).
The master of these studies is what we now know as Optimistic Rollup. In June 2019, the “Minimum Viable Merger Consensus” described this technology for the first time. Since then, the Ethereum community has vigorously supported ORU as a scalability solution for Ethereum-style smart contract execution, without waiting for Serenity Phase 2.
How Optimistic Rollup works
Optimistic Rollup visualization
As a two-way anchored side chain that minimizes trust (in other words, even if every verifier on the side chain is dishonest, there will be no stolen funds), ORU is very simple in operation (of course, my The “principle” is explained in more detail).
The aggregator collects the transactions on Rollup, packs them into the Rollup block, and sends the Rollup block together with the deposit (we will explain why the deposit is needed soon) to Ethereum (or another block similar to Ethereum) Chain, on which a smart contract with a large number of states is running). This Rollup block will not be translated or executed-the smart contract only records the block hash and tracks the hashes of all Rollup blocks. Rollup blocks themselves are not stored in smart contracts, but everyone can find them in Ethereum’s historical transactions.
The Rollup block contains a state root, that is, the root of the state tree of the Rollup block. If the state root is invalid, anyone can use the fraud proof to prove that it is invalid during the challenge period. This may be because a transaction in this Rollup block is invalid, or because the state root is invalid. If a Rollup block is proved to be invalid, the contract will roll back the Rollup chain, and all Rollup blocks following this invalid block will become orphan blocks. Once the fraud proof is successful, part of the deposit will be paid to the prover, and the remaining part will be destroyed.
If no one submits a fraud proof until the end of the challenge period, the contract will finalize the Rollup block and allow the aggregator to withdraw the deposit. When users retrieve money from the Rollup chain back to the main chain, they need to initiate a withdrawal request on the Rollup chain. The money can only be retrieved after the contract has finalized the Rollup block.
That’s it! ORU seems very simple. Why did it take so long to have a specific plan and implementation? This is because the design space of these technologies is actually unlimited, and “to find the answer, you must first find the right direction.”
Please note that the above is how ORU operates on blockchains such as Ethereum through on-chain execution. ORU can also be used as an application with client-side execution functions and implemented on projects such as LazyLedger. In the latter case, the fraud proof will be disseminated through a peer-to-peer network without publishing to the smart contract.
compromise
Although many features of ORU are essential to decentralized blockchains and unstoppable financial platforms and applications, there is a price to pay to achieve these features.
1. By default, due to the delay in interacting with the smart contract on Ethereum, the challenge period for fraud proof will be very long (up to several weeks), and this will cause withdrawal delays. Client-side execution can significantly shorten the challenge period. However, we only need to allow liquidity providers to provide withdrawal services through atomic swaps and charge a small fee to easily solve the delay problem. In fact, this is a new DeFi component: liquidity providers can use their liquidity to earn income by providing services.
2. The throughput of ORU is capped by the data availability throughput of Ethereum. In this case, we can treat ORU as a pseudo-shard. Multiple ORUs can run in parallel on the same data availability layer. Fortunately, data availability is easier to scale than execution. Projects such as LazyLedger have been specifically optimized to provide a highly scalable and universal data availability layer, allowing all Rollup projects to reach their full potential.
in conclusion
All in all, ORU has been widely recognized. This solution allows Ethereum (and even the blockchain) to fulfill the promise of sharding before Serenity Phase 2 goes online: it can help decentralized applications achieve scalable execution without compromising important attributes. The projects that build ORU infrastructure include Fuel Labs, Offchain Labs, Optimism, Hubble, etc. (this list is not complete, and there is no endorsement for them). The projects planned to be built on ORU are even harder to count!
Source link: coinmarketcap.com
