BA-05 · LESSON 13

The complete mempool lifecycle

KEY DEFINITIONS

Terms used in this lesson

RBF: Replace-by-fee: a policy for replacing an unconfirmed transaction with a conflicting one that pays more.
Spread: The gap between executable buy and sell prices in a market.
Coinbase transaction: The special first transaction in a Bitcoin block, which claims permitted subsidy and fees and has no ordinary prior-output input.
Outpoint: A transaction ID plus output number that identifies one exact prior output.

Follow admission, relay, conflicts, RBF replacement, block connection, reorg reconsideration, expiry, size eviction, and local policy differences.

35 min Difficulty 2/5 Not started

VISUAL MODEL

See the whole mechanism before going step by step

Use the diagrams to orient yourself. Then the guided explanation below teaches every part in depth.

4 explanatory views

CONCEPT-SPECIFIC MAP · mempool lifecycleA mempool candidate moves through local and chain-driven statesSelect any state to inspect its exact role.

RELATIONSHIP MAPOrdered mechanism flow

01
RECEIVETransaction A
Serialized bytes arrive from a wallet, RPC client or peer and remain untrusted.
02
ADMISSIONConsensus preconditions and local policy pass
One node's result does not become a network-wide decision.
03
MEMPOOLA with ancestors and conflicts
The node tracks a volatile dependency graph rather than confirmed state.
04
EVENTRBF, block, reorg, expiry or eviction
Several independent events can remove or reintroduce a candidate.
05
RECONCILEUpdate mempool against chainstate
Block connection and disconnection atomically change chainstate before candidate reconsideration.

Rule shown: Each node independently admits, relays, replaces and evicts candidates, then reconciles that volatile graph whenever blocks connect or disconnect.

STAGE 1 OF 5RECEIVE: Transaction A

Serialized bytes arrive from a wallet, RPC client or peer and remain untrusted.

Governing relationship: Each node independently admits, relays, replaces and evicts candidates, then reconciles that volatile graph whenever blocks connect or disconnect. Complete path: 1. RECEIVE, Transaction A. Serialized bytes arrive from a wallet, RPC client or peer and remain untrusted. 2. ADMISSION, Consensus preconditions and local policy pass. One node's result does not become a network-wide decision. 3. MEMPOOL, A with ancestors and conflicts. The node tracks a volatile dependency graph rather than confirmed state. 4. EVENT, RBF, block, reorg, expiry or eviction. Several independent events can remove or reintroduce a candidate. 5. RECONCILE, Update mempool against chainstate. Block connection and disconnection atomically change chainstate before candidate reconsideration.

1. State transitionWhat exists, what changes, and what results

BEFORE

Transaction A spends funding:0 at 2 satoshis per virtual byte and enters one node's mempool.

MECHANISM

Parse the transaction, obtain previous outputs, run consensus preconditions, detect conflicts and ancestors, then apply local standardness, fee and resource policy. Passing o…

AFTER

The mempool is a changing local candidate graph that must continuously reconcile with chainstate.

Text equivalent: Starting from Transaction A spends funding:0 at 2 satoshis per virtual byte and enters one node's mempool. The mechanism begins when Parse the transaction, obtain previous outputs, run consensus preconditions, detect conflicts and ancestors, then apply local standardness, fee and resource policy. Passing one node does not guarantee passing another. The resulting lesson is The mempool is a changing local candidate graph that must continuously reconcile with chainstate.

2. Mechanism pathSelect a stage to inspect its job

STAGE 1 OF 5

Check before admission

Parse the transaction, obtain previous outputs, run consensus preconditions, detect conflicts and ancestors, then apply local standardness, fee and resource policy. Passing one node does not guarantee passing another.

Complete path: 1. Check before admission: Parse the transaction, obtain previous outputs, run consensus preconditions, detect conflicts and ancestors, then apply local standardness, fee and resource policy. Passing one node does not guarantee passing another. 2. Relay by inventory: A node announces an accepted transaction identifier. Interested peers request the bytes and repeat their own checks before storing or forwarding it. 3. Track packages and conflicts: Parents, children and conflicting spends form dependency sets. Package fee and resource rules can differ from single-transaction scoring. 4. Remove or replace: A policy-compliant RBF replacement removes its conflicts and affected descendants. Expiry and memory pressure can evict valid candidates without making them consensus-invalid. 5. Reconcile with blocks and reorgs: Block connection removes confirmed transactions and conflicts. Block disconnection reverses chainstate first, then reconsiders disconnected non-coinbase transactions under current mempool rules.

3. Rule and failure boundaryWhat accepts the result and where it can stop

ACCEPTED PATH

Consensus preconditions protect possible block validity while local admission, replacement, package and resource rules protect one node's volatile state.

CHANGED CONDITION

Treating mempool presence as a network vote, durable storage, guaranteed mining, or confirmation confuses a local policy cache with the selected blockchain.

Important distinction: A transaction enters the Bitcoin mempool and waits there until a miner confirms it. Each node has its own mempool. A candidate can be absent, replaced, evicted, confirmed or reconsidered independently at different nodes.

Text equivalent: The accepted path is enforced by Consensus preconditions protect possible block validity while local admission, replacement, package and resource rules protect one node's volatile state. If the required condition changes, Treating mempool presence as a network vote, durable storage, guaranteed mining, or confirmation confuses a local policy cache with the selected blockchain.

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Learn the idea

A mempool is one node's volatile set of unconfirmed transactions that passed its current admission policy. It is not a shared network waiting room and not part of consensus state. Transactions enter after local checks, spread through independent peer decisions, leave through confirmation, conflict, replacement, expiry or size eviction, and may return after a reorganization.

GUIDED EXPLANATION1/5 ideas inspected

Check before admission

The worked example follows the explanation

Inspect every idea above to open it.

Important distinction“A transaction enters the Bitcoin mempool and waits there until a miner confirms it.”

Each node has its own mempool. A candidate can be absent, replaced, evicted, confirmed or reconsidered independently at different nodes.

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