Bitcoin: Is a spent UTXO immediately removed from the UTXO set?

Understanding Bitcoin’s UTXO System: Is a Spent UTXO Instantly Deleted?

In the world of cryptocurrencies, understanding how Bitcoin’s underlying technology works is crucial to making informed decisions. The most fundamental aspect of this technology is the UTXO (Unspent Transaction Output) set, which stores all unspent transactions that have been recorded on the blockchain.

In this article, we’ll dive into the details of Bitcoin’s UTXO system and explore what happens to a spent UTXO when it’s sent to the mempool.

What is an XRP Transaction?

Before we dive deeper, let’s briefly discuss what an XRP transaction is. An XRP transaction is a single instruction that updates multiple accounts with new or updated values. In Bitcoin, an XRP transaction simply moves funds from one account to another without updating their balances.

The UTXO Set: A Key Component of the Blockchain

In Bitcoin, every transaction creates two unspent outputs (UTXOs) in the UTXO set. The UTXO set is a crucial part of the blockchain because it keeps a record of all the transactions that have been recorded since the network was launched.

When a new transaction is created, its inputs are combined to create a unique hash. This hash serves as a reference for updating balances in the UTXO set. To update an account balance, the sender must specify which outputs they want to spend and when. The sender then broadcasts their transaction to the network, which includes the recipient’s address and the hashes of the inputs.

Spent UTXOs: What Happens When They Are Sent to the Mempool?

Now, let’s examine what happens to a spent UTXO when it is sent to the mempool. The mempool is a mechanism that allows new transactions to be added to the network without requiring miners to solve complex problems.

When an XRP transaction is created and broadcast to the network, it includes the recipient’s address and the hashes of the inputs (which represent the UTXOs). However, when this transaction is sent to the mempool, the UTXO pool will not be updated immediately.

The reason for this delay is that the mempool is a decentralized mechanism, meaning it is maintained by all nodes on the network. Each node adds new transactions to the mempool based on its own computational resources and available bandwidth. This process takes time because multiple nodes must agree before a transaction is added to the mempool.

Can a spent UTXO still be used?

Now that we have explored what happens to spent UTXOs when they are sent to the mempool, let’s answer the original question: can a spent UTXO still be used to perform another transaction?

The answer is yes. A spent UTXO can still be used in subsequent transactions because it exists within the UTXO pool and has not been deleted. However, the recipient must first retrieve the UTXO from the mempool using their private key.

Example Scenario: Spending 5 BTC

Suppose Alice wants to spend 5 BTC (25 million Bitcoin units). She broadcasts an XRP transaction that includes her wallet address as the recipient and the hashes of the inputs representing her 5 BTC. The transaction is then added to the mempool, along with other transactions from other users.

To use this spent UTXO, Alice must first retrieve it from the mempool using her private key. Once she has the UTXO in hand, she can add it to her wallet and make a new transaction with the recipient address as the sender and the updated value of 25 BTC (125 million units).

In short, Bitcoin’s UTXO system ensures that spent transactions are not immediately removed from the network. However, it takes some time for the mempool to process transactions and update the set of UTXOs. This means that a spent UTXO can still be used in subsequent transactions as long as it exists within the UTXO set and has not been removed from the mempool.