Mempool
blockchain · node
A node's local set of unconfirmed transactions accepted for possible relay and block inclusion.
- Also known as
- memory pool
A mempool is a node's local collection of unconfirmed transactions that passed its current consensus checks and relay policy in the available chain state. It is not part of consensus and it is not one shared network-wide queue.
Nodes can see different transactions because they connected at different times, use different policies, have different ancestors, or evicted entries under memory pressure. A transaction can be valid for a block yet absent from a particular mempool, and a policy-accepted transaction can later conflict or become invalid after a reorganization.
Miners commonly choose transactions by fee rate while accounting for parents, children, packages, signature-check and size limits, and local policy. When a block is accepted, nodes remove included transactions and any now-conflicting spends; other entries remain pending, expire, or are evicted.
A mempool dashboard is a snapshot of one node or provider. Counts, total bytes, fee bands, and waiting-time estimates can help describe pressure, but they do not guarantee another node's view or a transaction's confirmation time.
Read how blockchain congestion builds to connect pending transactions with demand and fees. Blockspace Lab lets you explore those relationships in a simulation.
Related terms
Transaction
→A serialized state transition that a blockchain can validate, relay, and include in a block.
blockchain · technical
Fee Market
→The rules and user demand that determine the price of scarce transaction inclusion or execution capacity.
blockchain · economics
Package Relay
→The ability for nodes to relay groups of related transactions together so miners evaluate fees on the package total.
mempool · policy
Zero Confirmation
→A transaction observed before any block has included it.
transaction · security