Mempool Incentive Compatibility

Mempool Incentive Compatibility

Original Postby sdaftuar

Posted on: February 13, 2024 19:19 UTC

The exploration of optimizing transaction ordering in Bitcoin's mempool to maximize fee collection presents several challenges and innovative solutions.

A key issue is the selection of transactions from the mempool, considering block size constraints and the goal of maximizing fees over time. Transaction dependencies complicate this task, necessitating a nuanced approach that considers the collective feerate of transaction sets or "chunks" for optimal ordering.

Feerate diagrams are introduced as a tool for visualizing and comparing different transaction orderings' efficacy. By plotting total fees against cumulative transaction size, these diagrams help identify the most efficient strategy. Constructing convex hulls of these diagrams allows for clear comparisons, aiding in the identification of an optimal transaction linearization that maximizes fee collection while adhering to size and dependency rules.

The concept of clusters, or topologically connected components within the transaction set, enables a more granular approach by linearizing clusters separately and then merging them. This method approximates optimal transaction selection across the entire mempool. Additionally, the complexities of Replace-By-Fee (RBF) policies are discussed, including the challenges of ensuring replacements lead to net benefits for miners without unintended consequences. Pieter Wuille's theorem and the cluster mempool proposal offer theoretical insights and practical solutions for managing and ordering transactions within the Bitcoin network, as detailed here and in the cluster mempool proposal.

The discussion extends to RBF policies, highlighting the inadequacy of simple fee and feerate comparisons due to the nuanced effects of transaction ancestry. An innovative approach considers a transaction's ancestor feerate when assessing its eligibility for replacement. However, this method may overlook actual mining dynamics, with examples showing that transactions with higher nominal scores might not be more attractive to miners.

Mining scores are proposed as a basis for an RBF rule, allowing new transactions to replace existing ones if they have higher mining scores and pay more in total fees. Yet, this is insufficient for guaranteeing a more profitable mempool configuration for miners due to transaction relationships. Feerate diagrams are explored as a tool for comparing different mempool configurations, though making definitive judgments between incomparable sets of transactions remains challenging.

A hypothetical scenario illustrates how the optimal choice between conflicting transactions might depend on broader network dynamics beyond mere transaction fees. Concerns about DoS attacks facilitated by lenient RBF policies are addressed, emphasizing the importance of ensuring transaction replacements lead to net increases in fees. Critiques of BIP 125 highlight the balance needed between fostering an open network and safeguarding against abuse.

Furthermore, the role of transaction fees in network relay dynamics is examined, with a focus on the minimum relay fee's implications for efficiency and security. The concept of mempool eviction is introduced as a mechanism to manage the mempool size, adjusting the feerate required for new transactions to cover the costs associated with eviction. This exploration into incentive-compatible behaviors and their resistance to DoS attacks contributes to understanding how to maintain network integrity and efficiency.