Definition
The mempool (memory pool) is where nodes keep unconfirmed transactions they have heard about on the network. Miners select transactions from their mempool when building a candidate block — typically prioritizing by fee rate (fee per unit of block space).
Source: Inventing Bitcoin — Ch. 5, Sovereignty Through Mathematics — Ch. 5
Behavior During Reorgs
If a block is orphaned (another chain tip wins under PoW rules), transactions from the dropped block are returned to the mempool if they remain valid under the new best chain. Conflicting spends are resolved by chain rules and ordering.
Source: Inventing Bitcoin — Ch. 5
Not Yet “In Time” for the Network
Until included in a valid block, a transaction has no consensus-defined timestamp in the same sense as a confirmed spend — the network’s notion of ordering is anchored in blocks, not the mempool alone.
Sources
Related pages
- Mining — block construction from the mempool
- outputs miners must validate
- Forks — stale blocks and mempool recycling
- Scarcity — block space as a scarce resource
- Difficulty adjustment — how hard blocks are to mine
- Lightning Network — moving activity off-chain from mempool competition
- Bitcoin — the base protocol