The Block Assembly Handshake: How miners pick from the mempool

13. The Block Assembly Handshake: How miners pick from the mempool

Miners are not "Volunteers"; they are "Profit-Seekers." When they build a block, they want to maximize their "Block Reward" (Subsidy + Fees). They reach into their local mempool and perform a "Search" for the most profitable combination of transactions. This process is called Block Assembly (handled in miner.cpp but powered by the mempool's logic).

For the Sovereign Architect, Block Assembly is the "Final Selection." It is the proof that the mempool's sorting logic (Chapter 3) directly defines the "Content of History."

Analyzing the Selection: CreateNewBlock

In the source code, we see how the node's mining logic asks the mempool for its "Best" entries.

/**
 * PEDAGOGICAL ANALYSIS: THE PROFIT MAXIMIZER
 * This logic builds a "Draft Block" by picking the highest 
 * fee transactions until the 4MB limit is reached.
 */
void BlockAssembler::addPackageTxs(int& nPackagesSelected, int& nDescendantsUpdated)
{
    // 1. Sort the mempool by "Ancestor Fee-Rate" (Chapter 6).
    // 2. Pick the top transaction.
    // 3. Does it fit in the 4MB block?
    // 4. If yes, add it! Update the "Current Block Fee".
}

Explaining the Selection: The Geometry of the Profit

• "The Ancestor Awareness": A miner cannot pick a high-fee "Child" without also picking its low-fee "Parent." The assembly logic is "Smart"—it evaluates the Package as a single unit of profit. It is the Holism of the Sovereign.

• "The Weight Limit": A block is limited to 4 million "Weight Units." The assembler must "Pack" the transactions like a game of Tetris to ensure not a single byte of space is wasted. It is the Efficiency of the Machine.

• "The Consensus Constraint": While picking transactions, the miner must also check for "SigOps" (Signature Operations). If a transaction uses too much CPU power to verify, the miner might skip it even if the fee is high. It is the Safety of the Protocol.

• "The Real-Time Update": The moment a block is found, the Mempool "Wipes" all those transactions from its RAM. The "Waiting Room" is suddenly empty of its most successful participants. It is the Cycle of the Core.

The Sovereignty of the Selection

Block Assembly is the "Fulfillment" of the mempool's purpose. It is where "Potential Truth" becomes "Permanent Truth." As a Sovereign Architect, you know that "Miners are the Servants of the Market." By understanding how they select transactions from the pool, you can design your payments to be "Irresistible" to the network. You are the "Master of the Selection."