Before we go into discussing optimistic rollups, some base knowledge is needed. One of which is blockchain scaling.
Blockchain scaling
Ethereum as a case study has grown to a level where the blockchain has hit some capacity limits. As a result, Ethereum network usage has become more expensive, necessitating scaling. The whole point of scaling actually is to increase transaction throughput (the number of transactions per second) and speed (faster finality) without compromising security or decentralization.
Scaling a blockchain ecosystem can be done in one of two ways
Increasing the capacity of transactions on the blockchain itself.
Modifying how you utilize the blockchain.
You can read more about scaling here
The second point highlighted involves users conducting the majority of their activity off-chain in an L2 ( Layer 2 ) protocol rather than directly placing all activity on the blockchain.
Rollups
Rollups is one of the types of layer-2 scaling. It can be refered to as a layer 2 hybrid scheme. The concept of Rollup is that Rollups keep some data per transaction on-chain while moving computation and state storage off-chain.
Here is a diagram that shows how rollups work
Source: vitalik.ca
Rollup Types
The two types of rollups are:
Optimistic rollups: also called fraud proofs
ZK rollups: also called validity proofs
Optimistic rollups
In optimistic rollups, the rollup contract records each batch's hash and the history of each state's roots. Optimistic rollups by default don't perform any computation. Instead, they suggest the new state to Mainnet after a transaction.
Optimistic Rollup L2 projects
Here are three projects that use the Optimistic Rollup Technology
Arbitrum
Arbitrum is a suite of Ethereum scaling solutions that enables high-throughput, low cost smart contracts while maintaining trustlessly security. Arbitrum supports all EVM language and natively supports all Ethereum tooling. Arbitrum Rollup differs from Ethereum in terms of price: transactions on Arbitrum only cost a small portion. It is quick and easy to port contracts from Ethereum to Arbitrum; no new software or code changes are required.
Website: arbitrum.io Documentation: developer.offchainlabs.com Explorer: explorer.arbitrum.io
Optimism
Optimism is a Layer 2 scaling protocol for Ethereum applications thus it makes transactions cheap. Optimism is intended to be an expansion of Ethereum. The CanonicalTransactionChain is a unique Ethereum smart contract that houses all Optimism blocks. Code in the CanonicalTransactionChain ensures that new Ethereum transactions cannot change the list of existing blocks. Users can send any messages between smart contracts on Optimism and Ethereum.
Website: optimism.io Documentation: community.optimism.io/docs Explorer: optimistic.etherscan.io
Boba Network
The foundation of Boba is actually the optimistic rollup created by Optimism. In addition to its emphasis on enhancing computing, Boba has it's own unique features such as: providing a swap-based system for quick exits from L2 to L1 (the standard exit period of rollups is 7 days) and an additional cross-chain messaging such as a message-relayer-fast.
Website: boba.network Documentation: docs.boba.network Explorer: blockexplorer.boba.network
A lot of developers are building on all 3 that I reviewed in this article. To get started with them, you can try out by deploying a contract. The following resources will help:
Conclusion
In this article, we have discussed blockchain scaling, the need for it, the various ways of scaling, rollups, optimistic rollups and finally projects whose technology are based on optimistic rollups.
I hope this article helped to keep things in perspective for someone out there.
References
vitalik.ca/general/2021/01/05/rollup.html ethereum.org/en/developers/docs/scaling l2beat.com