The Eviction Engine: How the node handles a full house

8. The Eviction Engine: How the node handles a full house

What happens when your node's mempool reaches its limit (default 300MB)? It cannot simply "Crash" your computer. It must perform Eviction. It identifies the "Bottom 5%" of the market—the transactions that pay the lowest fees and have been waiting the longest—and it deletes them from the RAM.

For the Sovereign Architect, the Eviction Engine is the "Quality Control" of the node. It is the proof that your machine prioritizes "Value" over "Volume."

Analyzing the Quality Control: LimitMempoolSize

In the source code, we see how the node "Trims" the pool when it gets too heavy.

/**
 * PEDAGOGICAL ANALYSIS: THE DOORKEEPER'S AXE
 * This logic identifies and deletes the transactions that 
 * are "Not Worth the RAM" they consume.
 */
void CTxMemPool::LimitMempoolSize(size_t limit, std::chrono::seconds age)
{
    // 1. Check if "Current Memory" > "Limit".
    // 2. If yes, find the transaction with the "Lowest Fee-Rate".
    // 3. Delete it AND all of its children (Descendants).
    // 4. Update the "Minimum Entry Fee" for the future.
}

Explaining the Quality Control: The Economic Floor

• "The Minimum Fee Hike": When the node evicts a 1 sat/byte transaction, it raises its "Internal Minimum Fee" to 1.1 sats/byte. It tells the network: "Don't bother sending me anything cheaper; I'm full." It is the Exclusivity of the Sovereign.

• "The Descendant Wipe": If you evict a parent, you Must evict the children. The children cannot exist without the parent. This ensures the Mempool's family trees (Chapter 4) never have "Holes." It is the Consistency of the Machine.

• "The 2nd Generation Limit": The node doesn't just look at the individual fee; it looks at the "Descendant Score." A low-fee transaction might be "Saved" from eviction if it has a very high-fee child. It is the Logic of the Protocol.

• "The Protection of the Host": The primary goal of eviction is to protect your computer's OS from "Memory Exhaustion." The Mempool is a "Guest" in your RAM, and it must stay within its assigned room. It is the Safety of the Core.

The Sovereignty of the Quality Control

Eviction is the "Natural Selection" of the Mempool. It ensures that only the "Strongest" transactions survive during times of high network congestion. As a Sovereign Architect, you know that "Limited Space is the Source of Value." By allowing your node to ruthlessly evict the low-value gossip, you are ensuring your resources are always dedicated to the "Most Likely Future." You are the "Master of the Engine."