What is a mempool

A mempool (memory pool) is the waiting area on a node where unconfirmed transactions sit until a miner or validator picks them up and adds them to a block. It matters because how full the mempool is drives the fee you need to pay: a crowded mempool means higher competition for block space and pricier transactions, while an empty one means cheap, fast confirmation. Every node keeps its own version, so the exact set of pending transactions can differ slightly node to node. For example, during the May 2022 Bitcoin fee spike, the mempool held over 100,000 unconfirmed transactions, pushing average fees past $6 as users bid to jump the queue. Tools like mempool.space let anyone watch this queue in real time.