The Core Issue: Cluster Mempool, Problems Are Easier In Chunks

Cluster Mempool, implemented by Suhas Daftuar and Pieter Wuille and merged into Bitcoin Core, is a significant architectural rework of how transactions are organized and sorted in the mempool. Previously, the mempool used conflicting metrics—ancestor feerate for eviction and descendant feerate for block construction—creating misalignments with miner incentives, which negatively impacted fee estimation, user reliability, and second-layer protocol security. The new system introduces the concept of a 'cluster'—a group of directly related unconfirmed transactions—which is further broken down into 'chunks' sorted by feerate. This structure allows for efficient block template construction by miners (grabbing highest feerate chunks first) and effective eviction (removing lowest feerate chunks first) while simplifying complex replacement logic. By keeping clusters and chunks small (e.g., a global cluster limit of 64 transactions), Cluster Mempool ensures computational practicality while aligning all mempool operations with optimal mining incentives.

(Source：Bitcoin Magazine)