Alternate PBS: A PBS Proposal for Based Rollups

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The Alternate PBS proposal for based rollups like Taiko aims to allow rollups to earn MEV income while addressing block stealing and MEV distribution, by introducing trusted proposers and a _backdoorFee() for L2 block proposals. Community feedback highlights concerns over potential censorship, the departure from traditional rollup models, and suggests focusing on the basefee concept and simplifying the proposal.

What is this about?

The discussion revolves around the Alternate PBS proposal, which is tailored for based rollups such as Taiko. This proposal seeks to enable the rollup to capture MEV income, addressing issues like block stealing and MEV income distribution. It introduces a set of trusted proposers, governed by a Proof-of-Governance protocol, who have exclusive rights to propose L2 blocks to L1 for each L1 block. A _backdoorFee() mechanism allows overriding the exclusive rights of trusted proposers, with the fee going to the L2 treasury. The proposal also touches on the timing of L2 MEV-Boost auctions, sequencing L2 blocks within L1 blocks, and finding a balance between permissionlessness and control through the _backdoorFee(). Additionally, Evan-forbes9 suggests simplifying the proposal by focusing on the basefee concept and excluding the round robin fork choice rule, which they believe could be implemented later or replaced with other schemes.

How is the community reacting?

Community members have expressed various concerns and provided feedback on the proposal. Jsky2 raised questions about the backdoorFee mechanism, potential issues, and the block proposing process. They also highlighted the risk of L1 proposers censoring L2 blocks and the separation of the backdoorFee payment from its associated L2 block. CTra1n3,4,5 offered clarifications and suggested design adjustments, such as setting the backdoorFee to zero for certain preconfirms and enhancing the expressiveness of the backdoorFee function. Gets7 pointed out the significant departure from traditional based rollups and questioned the design's characterization as an escape hatch. Evan-forbes9 proposed refocusing the proposal on the basefee concept and removing the round robin fork choice rule to maintain the benefits of a based rollup. The community is actively engaged in the discussion, exploring implications and potential enhancements to the proposal.

Why this is positive?

  • The proposal is designed to keep L2 block revenue within the L2 ecosystem.
  • It addresses block stealing by allowing only one block proposer per block through the trusted proposer set.
  • Maintains permissionless L2 block production by allowing anyone to pay a _backdoorFee() to bypass the trusted set.
  • Inherits L1 censorship resistance by permitting the trusted set to be overridden in case of suspected censorship.
  • Enables multiple L2 block proposals per L1 block, potentially increasing throughput.

Why this is negative?

  • The _backdoorFee() could be used to grief trusted proposers and turn block inclusion into an MEV auction.
  • There's a risk of Profitable Censorship MEV, incentivizing L1 proposers to censor L2 blocks.
  • Separating the backdoorFee payment from its associated L2 block may cause overhead and create censorship opportunities.
  • The proposal significantly deviates from the concept of pure-based rollups, which might not meet community expectations.

Next actions

We have not been able to determine the next actions for this proposal.

Posted 14 days ago

Last reply 4 days ago

Summary updated 4 days ago

Last updated 04/12 00:23