Glossary: Mempool

Glossary: Mempool

Glossary
2 min readUpdated: 25. February 2026 · By Makar

One-Sentence Definition

The mempool (memory pool) is a temporary storage area where unconfirmed cryptocurrency transactions wait until a miner includes them in a block.

Why It Matters for Solo Mining

When you’re solo mining, your full node maintains its own mempool that holds all the pending transactions it knows about. The transactions you choose from your mempool to include in your block template directly affect your potential earnings, since each transaction includes a transaction fee that you’ll collect if you successfully mine that block. Smart miners prioritize transactions with higher fees to maximize their reward.

How It Works

When someone broadcasts a transaction on a peer-to-peer network, it doesn’t immediately go into the blockchain. Instead, it gets sent to nodes across the network, and each node stores it in their local mempool. Your mining software constantly monitors your mempool and builds block templates using the most profitable transactions—usually the ones paying the highest fees per byte of data.

The mempool size changes constantly as new transactions arrive and old ones get confirmed. When the network is busy, the mempool fills up with thousands of pending transactions, and fees typically increase as people compete to get their transactions processed faster. Once a transaction gets included in a mined block and confirmed, it’s removed from the mempool.

Each node maintains its own mempool independently, so they might differ slightly depending on network propagation and node configuration. This is why different mining pools might have slightly different views of pending transactions.

Example

Think of the mempool like a restaurant kitchen’s order board. When customers place orders (transactions), they go up on the board (mempool) with different tip amounts. The chef (miner) picks the highest-tipping orders to cook first because they’re most profitable. Once an order is completed and served (included in a block), it’s removed from the board. During busy hours (network congestion), the board fills up with more orders, and customers offer bigger tips to get served faster.