In a significant advancement for Bitcoin’s transaction management, a new architecture known as Cluster Mempool has been developed by Suhas Daftuar and Pieter Wuille. This redesign of the mempool—the large pool of pending transactions—was officially integrated into Bitcoin Core with the approval of PR #336292 on November 25, 2025. The primary objective of this new system is to streamline the organization and sorting of transactions, facilitating better alignment with miner incentives and enhancing the security of second layer protocols.
The existing mempool structure, prior to version 30.0 of Bitcoin Core, employed a dual organization approach. It analyzed transactions based on their ancestor and descendant feerates, which are essential for determining transaction eviction and inclusion in block construction. However, this system exhibited inconsistencies, especially concerning mining incentives. When miners decide which transactions to include in their blocks, they must consider the average feerate of each transaction alongside its ancestors, complicating the decision-making process. When a node’s mempool is full, it may evict transactions based on feerates that do not accurately reflect which transactions miners are likely to prioritize.
This misalignment has created challenges in ensuring reliable signaling regarding transaction confirmations and fee estimations, particularly affecting second layer protocols that depend on accurate on-chain enforcement. The introduction of Cluster Mempool aims to resolve these critical blind spots by establishing a more systematic way of organizing transactions.
At the core of this new architecture is the concept of clusters, which group related unconfirmed transactions that interact with one another through outputs spending. Transaction dependencies are thus visualized as a directed graph, allowing for simpler and more effective management. Within these clusters, transactions are further broken down into smaller, manageable chunks, ranked by fee efficiency. This method permits miners to efficiently access the most profitable transactions for inclusion in their blocks while maintaining alignment with user expectations for fee estimations and confirmations.
The mechanics of this new structure mean that miners can now prioritize chunks based on the highest feerate while facilitating a smoother eviction strategy when the mempool reaches its capacity. This reduces unpredictable behavior during transaction replacements, simplifying the logic for fee-bumping strategies that determine which transactions take precedence in the queue.
The architecture also introduces a new global limit for clusters, capping each at 64 transactions and 101 kvB, ensuring that nodes can consistently maintain efficient pre-sorting without overwhelming computational demands.
This long-awaited upgrade promises to enhance mining decentralization, maintain equitable access to profitable transactions for miners, and create a more secure environment for second layer protocols. As the Bitcoin network aims to preserve its decentralized nature amidst growing user and developer needs, the implications of Cluster Mempool could significantly bolster the cryptocurrency’s functionality in the future.
For further insights into the technical intricacies of the Cluster Mempool implementation, interested parties can explore additional resources linked to the designs and functioning of the new system. As the evolution of Bitcoin continues, developments like these play a crucial role in shaping its robust framework for decentralized finance.
