Mining and Transaction Lifecycle Flashcards

Which of the following best describes the function of a node's 'mempool' in a blockchain network?

Answer: A temporary storage area for unconfirmed, but valid, transactions waiting to be included in a block.

The mempool, or memory pool, is a holding area within each blockchain node that stores valid, unconfirmed transactions. Miners select transactions from their mempool, typically prioritizing those with higher fees, to include in the next block they are attempting to mine.

In a Proof-of-Work system like Bitcoin, what is the primary purpose of the 'difficulty adjustment'?

Answer: To ensure that new blocks are found at a relatively consistent and predictable rate, regardless of changes in total network hash power.

The mining difficulty is a parameter that adjusts algorithmically (e.g., every 2016 blocks in Bitcoin) to target a specific average block time (e.g., 10 minutes). If blocks are found too quickly due to an increase in network hashing power, the difficulty increases. If they are found too slowly, it decreases. This maintains a stable block production schedule and predictable new coin issuance.

A miner is constructing a new block for a Proof-of-Work blockchain. They have selected a set of transactions from their mempool. What critical piece of information from the *previous* block must they include in the new block's header to ensure the chain remains unbroken?

Answer: The hash of the previous block's header.

The fundamental principle of a blockchain is the cryptographic linking of blocks. Each new block header must contain the hash of the preceding block's header. This creates a chronological and immutable chain, as changing any data in a previous block would alter its hash, which would in turn invalidate all subsequent blocks.

An exchange requires 6 confirmations before a user's Bitcoin deposit is considered final. What does '6 confirmations' signify in this context?

Answer: The transaction has been included in a block, and 5 subsequent blocks have been mined and added to the chain after it.

A transaction receives its first confirmation when it is included in a mined block. Each subsequent block added to the chain after that block counts as another confirmation. Therefore, 6 confirmations means the original block containing the transaction is now buried under 5 additional blocks, making it exponentially more difficult and costly to alter or reverse.

What is the first step in the lifecycle of a typical cryptocurrency transaction after it has been signed by the user's wallet?

Answer: It is broadcast to the network to be included in other nodes' mempools.

After a user signs a transaction with their private key, their wallet software broadcasts it to several connected nodes in the peer-to-peer network. These nodes then validate the transaction and propagate it further to their peers, ensuring it spreads throughout the network to eventually be seen by miners and enter their mempools.

Which of the following accurately describes a 'stale block,' often colloquially referred to as an 'orphan block'?

Answer: A valid block that is not accepted into the main blockchain because a competing block at the same height was accepted first.

A stale block is a valid block that is not part of the longest, valid blockchain. This typically happens when two or more miners solve a block at roughly the same time and broadcast it to the network. A temporary fork occurs, and as soon as one chain becomes longer, the block on the shorter, abandoned chain becomes a stale block. The term 'orphan block' is often used interchangeably, though it technically refers to a block whose parent is not yet known by the node.