Crypto glossary
Mempool
The mempool is the waiting area where valid but unconfirmed transactions sit until a miner or validator includes them in a block.
Short for memory pool, the mempool is the set of transactions a node has received and checked but that are not yet in a block. Each node keeps its own version, so mempools across the network are similar but never identical.
Block space is limited, so miners and validators usually pick the transactions that pay the highest fees first. When the mempool fills up during busy periods, fees rise and low-fee transactions can wait for hours or be dropped. Users can often speed up a stuck transaction by replacing it with a higher-fee version or by spending its output in a new transaction that pays extra.
Public mempools also expose pending trades, which is what allows MEV bots on Ethereum to front-run or sandwich them. Some users send transactions through private channels to avoid this.
Example
During a busy period, a Bitcoin payment offering 2 sat/vB may sit in the mempool for a day while transactions paying 20 sat/vB confirm in the next block.
Related terms
Latest articles on Mempool
- Aptos Activates Encrypted Mempool to Fight Front-Running as APT Unlocks Fall 60%
- Private Mempool Brings Notable Privacy Upgrades to Polygon’s Full Use‑Case Stack
- Aptos Proposes Encrypted Mempool for Transaction Privacy
- Polygon Introduces Private Mempool Delivering One‑Line MEV Protection
- Ethereum Proposes Encrypted Mempool EIP to Strengthen MEV Defense and Censorship Resistance
