Thread by @0xPolygon

1/11 Polygon aims to become the go-to scaling hub, and we're actively exploring major scaling solutions.

In parallel, we want to educate the community; understanding different solutions & their trade-offs are critical.

Today we talk about Rollups.

bit.ly/EthScalingWith…

2/12 We thank @EdFelten, @jadler0 and @gakonst for their valuable feedback.

So, what are Rollups?

Simply put, Rollups provide an easy way to bypass the problem of all Ethereum nodes having to execute txns present in a block, to verify the validity of included transactions.

3/12 ZK Rollups do this by executing txns off-chain and submitting proofs called validity proofs back to Ethereum.

Optimistic Rollups solve this by executing txns off-chain and submitting assertions on Ethereum, with an added challenge period. These are secured by fraud proofs.

4/12 But the obvious question arises - Which one is better? TL;DR: both ZK and Optimistic Rollups have their own set of advantages and drawbacks.

5/12 ZK Rollups:
✅ Pros: Cutting edge tech, lot of promise, do not depend on censorship resistance for security.
❎ Cons: ZKP Generation takes up significant resources, ZK circuit design is cumbersome, tradeoffs b/w trusted setup, proof generation costs and verification costs.

6/12 Optimistic Rollups:

✅ Pros: Support most Ethereum opcodes, easier migration.
❎ Cons: Lack of immediate withdrawals, liquidity challenges and dependence on censorship resistance for security.

7/12 But enough with technology, which one of these approaches is better for your money?

Both ZK Rollups and Optimistic Rollups today can handle financial transactions very well. However, what concerns users the most, is transaction confirmation times.

8/12 ZK: Operator picks up txn, user waits for proof generation, proof submission on Ethereum and corresponding ZK verification and finalization on Ethereum.

⏱ ~10 mins to few hours

Timings vary depending on the application, amount of batching, transaction complexity etc.

9/12 OR Withdrawals: Operator picks up transaction, submits it on-chain, user needs to wait for the challenge period.

⏱ 1-2 weeks, depending on rollup construction and on-chain consensus.

Times can be reduced by LPs, but this approach does not work for NFTs.

10/12 What is the current state of Rollups?

In the short term, rollups would significantly reduce transaction costs. Both the rollup variants have achieved high TPS.

11/12 There will be a ceiling to scalability offered, and even if rollups execute 1000s of transactions, all transactional data has to be submitted on-chain.

The amount of call data that the Ethereum network can hold will be exceeded as multiple Rollups deploy.

12/12 What does the future hold and what’s Polygon doing about it?

Polygon is working on solutions to these problems and we will explore this area further in the next series. We're excited about developments in Rollups and will continue to work with the top teams in the space.