Thread by @bkiepuszewski

1/ With @arbitrum Sequencer down for an hour, Arbitrum chain effectively reduced itself to L1 Ethereum wrt to cost and speed, but it never stopped working. How is it possible ? And why @l2beatcom claims that users should propose blocks when operator is down ? 🧵👇

2/ Arbitrum, as any L2 Optimistic Rollup, posts on Ethereum L2 transaction batches and, periodically, state roots of L2. Anyone can confirm that the latest state root of L2 is indeed the result of executing L2 transactions previously posted. Verify, don't trust !

3/ So, who is posting L2 txs on Ethereum ? Typically sequencer, but if Sequencer is down, users can do it themselves. This is what we mean by "transacting using L1". Users can do it if Sequencer is down, or if the Sequencer is censoring them

4/ What about state roots then ? These are posted by "Validators", separate entities from the Sequencer. And, during the Sequencer outage, they kept running, so technically Rollup was still chugging along even though Sequencer was down

5/ You can read more about Validators here: developer.offchainlabs.com/docs/rollup_pr… but you can also inspect their "work" onchain

6/ etherscan.io/address/0xddff… is one such validator. Not very informative, but let's have a look at one of these "Execute" transactions using @eth_tx

7/ Rollup.stakeOnNewNode is essentially saying "I am staking some ETH on the fact that the state root of a latest Block is 904c0c28bd352058c8e4f74c2c16bfc1d97c143f90338c89940661febee3f9e9" (for why it's called a Node and not simply a Block you need to ask @arbitrum, srsly)

8/ Now, other Validators can agree with that (by putting their stake into the same "Node"), or they can disagree creating alternative "Node" and entering a dispute.

9/ Need more details how to use Arbitrum directly from L1 ? Read excellent post from @DZack23 and yes, there is no good UI so far to do that

https://twitter.com/DZack23/status/1437923828391424005?s=20

10/ Finally, why @l2beatcom claims that users need to propose blocks when Operator is down ? Because if Validators were down, they themselves would have to become Validators and propose blocks. Here Operator means both Sequencer and Validators, I guess it should be more clear 🙏