Explain in non-technical language how Rollup realizes the expansion of Ethereum

0

252 total views

Rollup is a “draft paper” for complex calculations in Ethereum.

Written by: Benjamin Simon, Researcher at Mechanism Capital Compiler: Perry Wang

Let’s make an analogy first.

Imagine we are back in middle school math class. Our teacher, just as cruel as your middle school math teacher, listed us a hundred long division problems, each of which involves a large number. We are told that the task is to answer as many questions as possible. But there is a problem! We must write down the final solution and each calculation step on a piece of answer sheet. After a few minutes, with the uncomfortable feeling of sinking our stomach, we felt that this task was really ridiculously impossible. Only a few complete answers can be written on one page.

What does this Kafka-style story have to do with Rollups?

In this analogy, this answer sheet represents an Ethereum block, and the mathematical problem is smart contract transactions. Ethereum is currently very crowded. There are too many transactions to include in each block. To make matters worse, most of these transactions are computationally intensive, such as flash loans or transactions routed through aggregators. In the pre-DeFi era, only simple transfers and payments have become history.

This is the crux of the problem. Just as the mathematics teacher in the analogy asks us to stuff every line of difficult long division solution on a piece of paper, Ethereum must also process and record every line of calculation for every transaction.

The emergence of Rollups solutions changed this situation.

Rollups moves calculations off-chain, while only storing as little transaction data as possible on-chain. In this basic sense, they are draft papers of Ethereum’s calculations. Rollups handles all the messy data processing, so that exponential smart contract transactions are aggregated in a single Ethereum block in batches.

This analogy can help describe the problem Rollups aims to solve (“network congestion due to computational overload”). It even gave us a vague understanding of what the Rollups solution requires (“mobile computing is moved off-chain”). But as for how Rollups actually work, what they look like, and why they make people like me so excited-we need to study in depth.

What is Rollup?

Rollup is essentially a separate blockchain, but with some modifications. Like Ethereum, the Rollups protocol has a “virtual machine” (EVM) that executes smart contract code. The operation of the Rollup virtual machine is independent of Ethereum’s own virtual machine, but they are managed by the Ethereum smart contract. This connection allows Rollups to communicate with Ethereum. Rollups executes transactions and processes data, and Ethereum receives and stores the results.

At the technical level, the key difference between the Rollup chain and other more traditional blockchains is the way in which new blocks are generated.

Generally, a blockchain is maintained by a distributed network of parties (“miners” or “validators”, depending on the type of chain). These relevant parties jointly produce blocks through consensus. Simply put, the parties involved vote on how to process a set of transactions—or how to construct the next block. The block that has received the majority of support will become the block that is permanently written to the chain.

In contrast, the Rollup chain does not operate by the rule that the minority obeys the majority. Conversely, the party monitoring the status of Rollup can send so-called “assertions” back to Ethereum, stating how the transaction should be processed. The important thing is that Ethereum can accept or reject this assertion, regardless of whether most of the other parties in Rollup support this assertion. In practice, this usually means that one of the parties in Rollup is designated as the task of processing transactions and generating blocks.

Wait a minute… Is Rollups a centralized solution?

The centralized nature of Rollup block production is part of the reason why Rollup is able to process transactions so efficiently. But it also raises an obvious and worrying question: If there is no consensus of the majority, how does Rollup ensure that the block production is correct-what happens if the block producer happens to be malicious?

This kind of centralization confuses users who are accustomed to consensus-based blockchain encryption. In fact, if the story ends here, we may (incorrectly) conclude, as Avalanche co-founder Kevin Seqniqi recently said on Twitter that Rollup is just a “database copied by one party.”

In fact, as we will see, the so-called centralization accusations are more logically misleading than false. Normally, a centralized blockchain without a strong consensus mechanism is susceptible to corruption and hostile takeovers . However, in the unique situation of Rollup, the lack of decentralization does not actually cause security and integrity issues. To understand why this is the case, we need to dig deeper.

The important role of data availability

Recall the math homework problem we mentioned at the beginning. Our life-saving straw is draft paper that can be used for calculations so that we only need to write the question and its answer on the answer sheet. Rollups are like draft papers, we say that they “move smart contract calculations off-chain, while only storing as little transaction data as possible on-chain.”

In fact, the last link-the storage of transaction data on the chain-is critical to how Rollup works. In Rollup, only calculations (data processing) are in an off-chain state. Each transaction processed by Rollup still stores its input data (officially called “call data”) on Ethereum.

What is the importance of keeping transaction data on the chain? In the analogy of math homework, the last answer sheet we handed to the teacher included the long division question and its answer. Our teachers can check our results after the fact, even if the answer sheet does not include a separate calculation step. Similarly, the continuous availability of data on the chain means that the bottom layer of Ethereum can repeat any calculations on Rollup.

In short, Rollups’ on-chain data availability means that there can be a built-in review process. Ethereum can “review” the integrity of the transactions processed on the Rollup chain, and then write them permanently into the ledger – just like the judicial review power of the Supreme Court of the United States.

Restricted power

Therefore, the key gold content of Rollup lies in its limitations. Rollups only push transactions to the bottom layer; they cannot be forcefully accepted because Ethereum can overturn any Rollup transaction if necessary. Because they are subject to this review process, it is said that Rollup transactions are not truly final.

Given the restricted nature of Rollup, we can come back to the unresolved centralization allegations. Individual block producers in Rollup may try to maliciously process transactions. But if so, Ethereum will simply reject the batch after the review process is complete, and the block producer will be punished.

Now, how exactly the “review process” works depends on whether Rollup is an Optimistic mechanism or a zero-knowledge mechanism (click here to learn more). But for both, the review process has an exponential advantage over the efficiency of Ethereum without Rollup in processing transactions on its own.

In short, the Rollup system is based on the principle of “checks and balances” to ensure that Ethereum is still a sovereign chain; Ethereum’s own consensus is the ultimate arbiter of truth. But importantly, this is different from side chain solutions. Due to the lack of the same review process, the side chain handles transactions through its own, completely independent consensus mechanism. Sidechain transactions are “final,” while Rollup transactions are not (the finality is not established until they are confirmed on Ethereum). Therefore, side chains require higher trust assumptions because they cannot benefit from Ethereum’s own decentralized security mechanism. In fact, I think sidechains are more similar to EVM-compatible layer 1 solutions than Rollup.

to sum up

In a nutshell: Rollups’ solution is to move the calculations off-chain to free up more on-chain space. The availability of on-chain data is crucial because it means that Ethereum can carefully check the integrity of Rollup transactions. In turn, this review process can be used as a “check” of Rollup block production, and Rollup therefore does not need a consensus mechanism.

Rollups can finally allow Ethereum to have a large enough market (cake) and eat this cake: they release more on-chain capacity at an exponential level without destroying the security of the network’s decentralization. At least in my opinion, this is as elegant as the expansion solution we are looking forward to.

Thanks to t11s and Hasu for their contributions and suggestions.