Mempool

The mempool (memory pool) is the holding area for transactions that have been broadcast to a network but not yet confirmed in a block. Each node keeps its own view of pending transactions.

How it works

When you send a transaction, it spreads across the network and waits in the mempool until a miner or validator selects it for the next block. Because block space is limited, those offering higher fees are generally picked first. Once a transaction is included in a confirmed block, it leaves the mempool.

Why it matters

The size of the mempool is a real-time measure of congestion: a crowded mempool means longer waits and higher fees, while an empty one means transactions confirm quickly and cheaply. Watching it helps users decide what fee to attach.

Example

During a surge in activity, thousands of transactions can pile up in the mempool, pushing fees higher.

Mempool: Frequently Asked Questions

What happens to a transaction while it sits in the mempool?

After you broadcast a transaction, it spreads across the network and waits in the mempool until a miner or validator selects it for the next block. Because block space is limited, those offering higher fees are generally chosen first. Once the transaction is included in a confirmed block, it leaves the mempool and is no longer pending.

How does the mempool affect the fees I should pay?

The mempool's size is a real-time gauge of congestion. When it is crowded, many transactions compete for limited block space, so you generally need a higher fee to be picked promptly. When it is nearly empty, transactions confirm quickly and cheaply. Watching the mempool helps you choose a fee that balances speed against cost.

Why might my transaction stay stuck in the mempool?

If you attach a fee that is too low relative to current demand, miners or validators may keep prioritizing higher-fee transactions, leaving yours waiting in the mempool. During surges, thousands of transactions can pile up and push fees higher. The transaction is not lost; it remains pending until it is included in a block or eventually dropped.

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