Rollup is considered a definitive opportunity. As the congestion problem of Ethereum becomes increasingly prominent, more and more projects are trying Rollup solutions, including Synthetix, Uniswap, MCDEX and so on.Four Rollup Solutions
There are currently four main Rollup solutions, Optimistic Rollup, ZK Rollup, Arbitrum, and Validium.All Rollups are doing several things, one is to aggregate multiple transactions under the chain and perform batch calculations (write transactions); the other is to verify whether the transactions are correct and ensure that the data placed on the chain is safe ; The third is to write the confirmed final state to the chain.The difference between the four Rollup solutions mentioned above is mainly in the "transaction verification" link. "Transaction verification" is actually a trade-off between Rollup security and expansion effects.On the one hand, there must be a feasible method to verify transactions, and problematic transactions and data cannot be brought to the chain, destroying the security of Layer1. On the other hand, too much verification data and processes cannot be put on the chain for safety, so that the expansion effect of Rollup will be greatly reduced.-ZK Rollup verifies transactions through the zero-knowledge proof technology zk-SNARK. The full English name of zero-knowledge proof zk-SNARK is zero knowledge-sufficient non-interactive argument of knowledge (zero knowledge-sufficient non-interactive knowledge argument).As can be seen from the name, zero-knowledge proof zk-SNARK is a "sufficiency" verification method, just like solving a math problem, with strict proof logic, logically forward reasoning, and no loopholes in the process. Therefore, ZK Rollup is the most versatile and most secure of the four schemes.But at the same time, it is very difficult to produce the entire verification logic of ZK Rollup. This is why ZK Rollup is suitable for some simple transactions, but it is still difficult to support virtual machines (VMs), because it is too difficult to verify these complex smart contracts, and major teams need to study slowly.-Validium also uses zero-knowledge proof zk-SNARK. The biggest difference between it and ZK Rollup is that the data is only available off-chain, and the transfer of accounts on the chain needs to be authorized by off-chain users. This introduces the risk of off-chain centralization to a certain extent. There are also some views that classify Validium as a ZK Rollup solution.-The Optimistic Rollup mainly conducts transaction verification through "economic challenges", which is like doing a question to eliminate wrong answers and make the final state closer to correct.It can be seen that this verification process is not sufficient, but the verification process is simpler. So Optimistic can support smart contracts. Optimistic Rollup has its own built-in virtual machine VM. At present, projects on Ethereum need to be processed and converted to be transferred to Optimistic. Compared with ZK Rollup, Optimistic is more convenient for developers, but less secure.Rollup application status
Rollup is a direction publicly recognized by the Ethereum team. In the Bihu 3rd Anniversary AMA, Vitalik said that "Rollup is more suitable than ETH2.0 to solve the current expansion problem".
Projects that adopt Rollup or have related plans
Optimism
Develop Optimistic Rollup with Offchain LabsUniswap V3
Optimistic Rollup may be usedProgress: Regarding when the V3 version of Uniswap will be launched, Andre Cronje, the founder of yearn.finance, guessed yesterday that there may be big progress soon.One thing that people look forward to in V3 is the possibility of being a Layer 2. Hayden Adams, the founder of Uniswap, once said on Twitter that "when the production side is ready, V3 may be deployed to Rollup that supports the Solidity language."
Source: Twitter
It can be seen that the Uniswap project party may choose the Rollup solution from the perspective of development friendliness, and Optimistic Rollup is also the solution that the community generally believes that Uniswap will choose.Synthetix
Progress: Rollup has been launched. Synthetix can be said to be one of the first projects to try Rollup and progress the fastest.According to the official statement, because the codes of Layer1 and Layer2 are incompatible, the smart contracts of Synthetix on Layer1 need to be processed before they can run on Optimistic. In order to minimize risks, Synthetix adopts a gradual migration strategy and gradually adds functions to Layer 2. Now Synthetix has implemented the pledge function on the Optimistic network.The Synthetix project said that the migration to Layer 2 will focus on two aspects - "staking" and "transaction". Synthetix wants to realize that Layer 1 and Layer 2 support transaction functions at the same time, and completely transfer the pledge function to Layer 2. On this basis, the deployment of Synthetix on Optimistic will be divided into multiple stages. The first few stages are mainly:Phase 0: SNX’s one-way bridge from Layer 1 to Layer 2, casting of sUSD, and claiming of SNX tokens (Beep News Note: sUSD is an intermediate asset used by Synthetix to mint synthetic assets. At this stage, SNX on Layer 2 and sUSD are not tradable)Phase 1: Realize the transaction of sUSD and other synthetic assets, the transfer of SNX and synthetic assetsPhase 2: Bidirectional SNX bridge between Layer1 and Layer2Synthetix has very complete functions on Layer 1, including transactions, derivatives, asset management, etc., so as this project advances on Optimistic, its Layer 2 status is quite exciting.
Volmex
Progress: In testnet stage. The Volmex platform will provide financial instruments such as the Ethereum Volatility Index. In order to achieve cheaper and faster index queries and futures transactions, Volmex is already trying Rollup.Saddle
Progress: Smart contracts are being migrated to Optimistic. Saddle is an automated market-making tool for price-anchored crypto assets. The project party stated on Twitter that it is currently migrating smart contracts to the Optimistic network to achieve instant transactions and low handling fees.Celer
Progress: Launched Layer2.finance, a DeFi expansion and acceleration solution based on Optimistic Rollup. Celer Network is a Layer 2 expansion project of Ethereum. Like other Rollups, users can deposit funds into the Rollup chain of Layer2.finance by performing a deposit transaction on the Rollup contract on Layer1, but Layer2.finance will not migrate the DeFi protocol itself to Layer2.zkSync
The ZK Rollup scheme created by Matter LabsProgress: The main network has been launched, but as mentioned above, ZK Rollup is relatively difficult, and zkSync has not yet provided a general solution for Rollup.
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Loopring
Layer 2 protocol based on ZK RollupProgress: The main network has been launched. Although there is no clear information on whether Loopring is universal, considering the complexity of ZK Rollup, Loopring is likely to have no universal solution like zkSync.The Loopring team has always been very optimistic about the second-layer network. The team estimates that by June this year, more than 10% of Ethereum Layer1 transactions will be carried by Layer2. As a common feature of the ZK Rollup solution, Loopring also emphasized its own advantages on the official website: the same level of security as Layer 1; high performance, TPS up to 2000+/s; low handling fee, less than 0.001 RMB/transaction.Curve
Progress: Curve's relatively big progress on Rollup was in October 2020, when it and zkSync jointly launched the Layer 2 smart contract testnet. Curve is the first DApp to settle in.Sushiswap
Progress: Sushiswap stated in the roadmap at the beginning of this year that it will adopt zkSync's Rollup solution together with the Yearn ecosystem. It is worth noting that Uniswap may adopt Optimistic Rollup. This is another choice that Sushiswap has made different from Uniswap since it cloned Uniswap. Sushiswap is indeed very independent and dynamic.Balancer
ZKSwap
Progress: Mainnet has been launched. ZKSwap is a Layer2 DEX based on ZK Rollup. Recently, ZKSwap has been more incentivized for Layer 2 users. On the one hand, long-term token incentives will be provided to users who provide liquidity. On the other hand, token airdrops have been carried out to token holders, etc.Storji
StablePay
Golem
Numio
Progress: Numio is a blockchain-based payment and storage application. At present, Numio has launched a wallet application, and this mobile application supports Layer2. Numio officially stated that it uses the zkSync scheme on Layer2.Rails
Aztec
Progress: The mainnet is about to go live. Aztec is a project focused on the privacy direction of the blockchain. In January of this year, Aztec cooperated with the Rollup-focused StarkWare project to launch a software protocol for zero-knowledge proof zk-SNARK applications, which are specifically applied in Rollup-related scenarios.Hermez
Arbitrum
Ethereum Rollup scheme created by Offchain LabsProgress: The mainnet is about to go live. As mentioned above, Arbitrum is similar to the Optimistic Rollup solution, but Arbitrum directly supports the Ethereum virtual machine EVM, and also supports other virtual machines VM, and the corresponding risk will be greater than Optimistic Rollup.MCDEX
Bancor
Progress: Deployed to Arbitrum testnet. As the originator of the AMM concept, Bancor has been iterating and innovating since the end of last year, including Layer 2.Bounce
Hop
Swapr
Progress: Deployed to Arbitrum testnet. Swapr is a forked version of Uniswap, a governable AMM. Both Swapr and the aforementioned Rails are projects in the DXdao ecosystem and part of the expansion strategy of DXdao. Rails uses the ZK Rollup solution, while Swapr uses the Arbitrum solution.Augur
Cometh
DAOstack
Progress: Plan to support the deployment and maintenance of all Layer2 DAOs. DAOstack is a system dedicated to decentralized coordination on Ethereum, providing support for decentralized organizations, funds, and markets.StarkWare/StarkNet/StarkEx
Progress: StarkWare is a zero-knowledge proof zk-SNARK research institution. StarkNet is the Rollup network developed by the institution. StarkEx is the first batch of applications of StarkNet. StarkEx has been launched on the main network.The Validium technology mentioned above is also a Layer 2 solution launched by StarkWare. Many people classify StarkNet into the category of ZK Rollup. The difference between StarkNet and ZK Rollup is that StarkNet uses STARK technology in zero-knowledge proof instead of the more common SNARK. In this article, Beep News classifies Rollups related to StarkWare into Validium. There may be differences in the classification methods, which are explained here.dYdX
Paraswap
DeversiFi
Immutable
Progress: Immutable X, an NFT trading platform based on StarkWare, will be launched soon. Immutable is the development company of the famous Ethereum card game Gods Unchained, and the company is working with StarkWare to develop Immutable X. Immutable Twitter information shows that Immutable X will be launched soon, when Gods Unchained users have the opportunity to become the first batch of experiencers of this trading platform.BadgerDAO
"Four Mainstream Rollup Solutions and Popular DeFi Layer 2 Progress Inventory" by Blockchain Research Institute"Come, draw the key points for the first batch of EVM-compatible Rollup application ecology" by Lianwen"Ethereum Layer 2 Ecological Update: Two Top Protocols Complete Financing, Celer Proposes New Ideas for Capacity Expansion" by Lianwen 
