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A Quick Look at Optimistic Rollup

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Why does it get Ethereum developers and scalability researchers so excited?

Original title: "Introduction| Minimalist Explanation of Optimistic Rollup"

Original source: Ethereum enthusiasts

Nowadays, for Ethereum Optimistic Rollup is the most promising scalability solution for Blockchain and even for all blockchains. But what is an Optimistic Rollup (ORU)? Why does it get Ethereum developers and scalability researchers so excited?

In this article, we will To introduce the basics of ORU.

Features

ORU has many desirable features. Among all blockchain scalability technologies, its characteristics are unparalleled. A properly designed ORU system will have the following characteristics:

- Trustless. Unlike traditional sidechain technologies, ORU is trust-free (or more professionally, trust-minimized). You can withdraw your funds from Rollup at any time without trusting that the vast majority of block producers on ORU are honest.

- License free. Unlike Plasma, ORU is permission-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 the next leader is elected is an implementation-specific problem, not a fundamental limitation.

- Hosting free. As mentioned above, because ORU is both trustless and permissionless, you can withdraw your funds at any time, and no one can stop you. Therefore, ORU is hosting-free.

-Expressive. Unlike ZK rollup, ORU (from Both theoretically and practically) are highly expressive. Whether it's a Bitcoin-like UTXO payment, or a full-fledged EVM-compatible implementation, ORU can handle it.

- Open for participation. Unlike payment channels, ORU supports smart contracts, and like Uniswap is open to everyone.

- Capital efficient. Unlike payment channels, ORU does not require users to lock funds in advance.

-Anti-chain congestion. Unlike payment channels and Plasma, ORU is resistant to on-chain congestion because ORU's fraud proofs are at the block level, rather than 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 immediate) finality. Unlike ZK rollup, ORU does not require proof of generation, so ORU blocks can be published to Ethereum immediately. Since valid ORU blocks cannot be rolled back, once these blocks are published on Ethereum, it is possible to achieve Ethereum-like finality.

A brief history of Optimistic Rollup

The earliest move to enhance the scalability of Bitcoin One is sidechains. The sidechain is a blockchain that runs together with the parent chain, but has different characteristics: shorter block generation time, larger block size, and more expressive smart contracts. However, normal sidechains have a fatal flaw: if the vast majority of miners/validators on a sidechain are dishonest, user funds can be stolen.

There have been many technologies over the years that have attempted to enhance sidechain to ensure that user funds will not be stolen even if the vast majority of participants are dishonest (this is known as trust-minimized two-way anchoring). An earlier example is merged mining (merged mining) 、 shadow chain (shadow chain), Then came Plasma and ZK rollup. Interestingly, before ORU appeared, a similar scheme was delayed state execution (we'll get to that shortly!).

The culmination of these studies is what we know today as Optimistic Rollup. The Minimal Viable Merged Consensus first described this in June 2019. one technique. Since then, the Ethereum community has strongly supported ORU as a scalability solution for Ethereum-style smart contract execution, No need to wait until Serenity Phase 2.

How Optimistic Rollup Works

< img src="https://image.theblockbeats.com/upload/2020-12-06/f5e2058b06a8d848063f43e78681c22fd5fce229.png?x-oss-process=image/quality,q_90/watermark,image_d2F0ZXJtYXJrbmV3Ln BuZz94LW9zcy1wcm9jZXNzPWltYWdlL3Jlc2l6ZSxQXzMw,g_center">

- Optimistic Rollup visualization-

As a trust-minimized two-way anchor sidechain (in other words, Even if every validator on the sidechain is dishonest, there is no chance of funds being stolen), ORU is surprisingly simple in the way it works (of course, my article "Principle" for more details).

-The aggregator collects the transactions on the rollup, packs them into the rollup block, and puts the rollup block together with the deposit (we will soon will explain why a security deposit is required) together with Ethereum (or another Ethereum-like blockchain running a so_no_worries_ethereums_long_term_value_is_still/djt6opz/" target="_blank">smart contracts with a large number of states). This rollup block is not translated or executed - the smart contract just records the block hash and keeps track of the hashes of all rollup blocks.

-rollup blocks themselves are not stored inside the smart contract, but anyone can find them in Ethereum's transaction history. A rollup block contains a state root, which is the root of the state tree for that rollup block. If the state root is invalid, anyone can prove it during the challenge period using a fraud proof it is invalid. This could be because a transaction in the rollup block is invalid, or because the state root is invalid. If a rollup block proves to be invalid, the contract will roll back the rollup chain, and all rollup blocks following the invalid block will become orphan blocks. Once the fraud is proven successful, part of the deposit will be paid to the prover, and the rest will be destroyed.

- If no one submits a fraud proof by the end of the challenge period, the contract finalizes the rollup block, allowing the aggregator to get back the deposit. When the user withdraws the money from the rollup chain to the main chain, he needs to initiate a withdrawal request on the rollup chain, and the money can only be withdrawn after the contract finalizes the rollup block.

That's it! ORU seems very simple, why did it take so long to have a specific solution and implementation? This is because the design space for these technologies is virtually unlimited, and "to find out, you have to Find the right direction first".

Please note that the above describes how ORU works on blockchains such as Ethereum through on-chain execution.

Compromise

Although many features of ORU are suitable for decentralized blockchain and Unstoppable financial platforms and applications are critical, but achieving these features comes at a price.

- By default, fraud proofs have a long challenge period (up to several weeks), and may cause delays in withdrawals. Client-side execution can drastically reduce the challenge period. However, we can easily solve the delay problem by simply letting liquidity providers provide withdrawal services through atomic swaps and charging a small fee. In fact, this is a new DeFi component : Liquidity providers can earn income by providing services and using their liquidity.

- ORU Throughput Ethereum's data availability throughput is an upper bound. In this case we can think of the ORU as a pseudo-shard. Multiple ORUs can Running in parallel on the same data availability layer. Fortunately, data availability Easier to scale than execute. LazyLedger are optimized to provide a highly scalable common data availability layer, allowing all rollup projects to reach their full potential.

Conclusion

In summary, ORU has been widely accepted. This solution allows Ethereum (and even the blockchain) to move into Serenity Phase 2 realizes the promise of sharding before it goes live: enabling scalable execution of decentralized applications without compromising important properties. Projects building ORU infrastructure include Fuel Labs, Offchain Labs, Optimism Hubble etc. (this list is not complete and does not mean to endorse them). There are countless projects planned to build on ORU!