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Satoshi Gazette
Glossary

Mempool

A node's own pool of valid transactions not yet confirmed in a block. Every node keeps its own, under its own policy and size limit, so there is no single mempool.

Protocol and network

Definition dated

also memory pool

Before a transaction is confirmed it lives in mempools. Each full node checks it against the consensus rules and its own relay policy, keeps it in memory and passes it to its peers; miners build their block templates from their own mempools.

Bitcoin Core caps the pool by the memory it uses, 300 MB by default. When the pool is full the node evicts the transactions paying least per vbyte and raises the minimum fee rate it will accept until the pool drains. The getmempoolinfo call reports the count, the total virtual size and the memory used as separate numbers.

The Network tab reads one node, mempool.space's. Its queue by fee band is that node's projection of how the next blocks would fill if nothing new arrived. Another node would show a similar picture, but not the same one.

Common misreadings3

  • People say

    The mempool is one global queue

    Precisely

    Each node holds its own. Relay policy, size limits and when a transaction arrived make them differ; the desk shows mempool.space's node.

  • People say

    A transaction dropped from the mempool is cancelled

    Precisely

    Eviction removes it from that node's memory only. It stays valid until one of its inputs is spent elsewhere, and can be rebroadcast and still confirm.

  • People say

    A full mempool means the network is failing

    Precisely

    It means more block space is wanted than the next blocks hold. The node raises its minimum fee rate and the lowest payers wait or drop out.