Mempool
A node’s local ‘waiting room’ for unconfirmed transactions, which miners draw from when creating new blocks.
When you broadcast a Bitcoin transaction, it goes to the mempool (memory pool) of each node, waiting until a miner includes it in a block. Each node maintains its own mempool policy—like minimum fee or size limits—so mempools can differ. During congestion, lower-fee transactions may linger for extended periods or get dropped. Tools like fee estimation analyze the mempool’s state to suggest fees that will confirm in a target timeframe. Once a transaction confirms, it’s removed from the mempool.
Key takeaways
Holds pending transactions awaiting confirmation
Policies differ, so not all nodes have identical mempools
Fee estimation and RBF rely heavily on mempool dynamics
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