Post Cluster Mempool: Mining and Fee Estimation (Bitcoin Core Dev Tech, May 2026)

Building on cluster mempool (the reworked mempool that groups related transactions into clusters and linearizes them by fee rate), this session walked a commit series that emits a new MempoolUpdated validation-interface notification on each mempool mutation, carrying the before/after fee-rate-diagram chunks of the affected clusters.

The intended consumers are efficient mining (incremental block-template updates) and chunk-based fee estimation, with most changes described as minimal and mechanical. A notable detail is handling reorgs that burst the cluster size limit via a two-stage optimistic-then-rollback process, since oversized clusters cannot be linearized to produce a valid before/after diff; chunk hashes are computed lazily on the scheduler thread because the update path is hot. The stated motivation, versus simply rebuilding the block template every second, was reduced redundancy and lower memory use when a fee increase is not in the top of the block template.