What Is Bitcoin Cluster Mempool?

Definition

Bitcoin Cluster Mempool is a Bitcoin Core mempool design that groups unconfirmed transactions connected through parent-child dependencies into clusters.

Overview

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Context and purpose
How it works
Practical checks and failure points
Related concepts
Further reading
Official implementation reference

Context and purpose

Bitcoin Cluster Mempool is an architecture used by Bitcoin Core to organize related unconfirmed transactions inside the mempool . A cluster is formed from transactions connected by unconfirmed spending relationships. If transaction B spends an output created by transaction A, they belong to the same dependency graph. Grouping these relationships explicitly allows the node to reason about the combined fee incentives of parents, children, and larger packages rather than evaluating every transaction as an isolated item. A chunk can contain one or more transactions that should be considered together because a low-fee parent may only be economically attractive when paired with a higher-fee child. The resulting feerate diagram supports more consistent choices for mining, mempool eviction, relay, and replacement. It also reduces edge cases created by older ancestor and descendant accounting rules, where different algorithms could rank the same package differently.

How it works

A Bitcoin mempool policy may evaluate related unconfirmed transactions as a package or cluster rather than treating each one in isolation. Cluster-level relationships affect relay and replacement behavior under specific software policies.

Practical checks and failure points

Verify the Bitcoin Core version and its actual relay policy; never equate local mempool acceptance with block inclusion or consensus finality.

Block Transaction Root · Blockchain Synchronization

Official implementation reference

The Bitcoin Core 31.0 release notes explain cluster limits and the getmempoolcluster RPC. Policy settings can change between releases; verify the deployed node version.

Bitcoin Core 31.0 release notes

Example

A child transaction depends on an unconfirmed parent. Fee-bumping and relay decisions may depend on the combined ancestry rather than the child's fee rate alone.

Comparison

Mempool policy controls what a node relays; miners' inclusion choices and consensus validation are separate.

Key Takeaway