With Ethereum's transition from Proof-of-Work to Proof-of-Stake in September 2022 came another paradigm shift, the Proposer-Builder Separation (PBS) scheme. PBS was introduced to decouple the roles of selecting and ordering transactions in a block (i.e., the builder), from those validating its contents and proposing the block to the network as the new head of the blockchain (i.e., the proposer). In this landscape, proposers are the validators in the Proof-of-Stake consensus protocol, while now relying on specialized block builders for creating blocks with the highest value for the proposer. Additionally, relays act as mediators between builders and proposers. We study PBS adoption and show that the current landscape exhibits significant centralization amongst the builders and relays. Further, we explore whether PBS effectively achieves its intended objectives of enabling hobbyist validators to maximize block profitability and preventing censorship. Our findings reveal that although PBS grants validators the opportunity to access optimized and competitive blocks, it tends to stimulate censorship rather than reduce it. Additionally, we demonstrate that relays do not consistently uphold their commitments and may prove unreliable. Specifically, proposers do not always receive the complete promised value, and the censorship or filtering capabilities pledged by relays exhibit significant gaps.

翻译：随着以太坊于2022年9月从工作量证明过渡到权益证明，另一场范式转变随之而来，即提议者-构建者分离（PBS）机制。PBS旨在将区块内交易的选择与排序职责（即构建者）与验证区块内容并将其作为区块链新区块提交至网络的职责（即提议者）分离。在此架构中，提议者是权益证明共识协议中的验证者，但现在依赖专门的区块构建者来创建能为提议者带来最高价值的区块。此外，中继充当构建者与提议者之间的中介。我们研究了PBS的采用情况，结果表明当前格局在构建者与中继间呈现出显著的中心化趋势。同时，我们探究了PBS是否能有效实现其预期目标——使业余验证者能够最大化区块收益并防止审查。研究发现：尽管PBS确实赋予验证者获取经过优化且具有竞争力的区块的机会，但它倾向于加剧而非减少审查现象。此外，我们证明中继并未始终履行其承诺，且可能并不可靠。具体而言，提议者并不总能获得完整承诺的价值，而中继所承诺的审查或过滤能力也存在显著缺口。