Skip to content
Satnam SatoshiIn service of humanityFind your place ↗
Menu
Lesson 09 / 21 · Advanced

Mempools and policy are not consensus

Understand why nodes can disagree about pending transactions.

14 MIN WITH PRACTICEREAD → TRY → REFLECTNO WALLET NEEDED

By the end, you’ll be able to…

  • Distinguish local relay policy from block validity.
  • Explain why a transaction can be absent from one explorer.
Your learning map

Three questions to carry into this lesson.

01Distinguish local relay policy from block validity.
02Explain why a transaction can be absent from one explorer.
Use these goals to guide your reading. Try the paper exercise, then explain the result in your own words.

There is no single global waiting room

A node’s mempool is its local collection of accepted unconfirmed transactions. Nodes can receive information at different times, apply different policies and evict transactions under resource constraints. An explorer showing no result does not prove that nobody else has seen the transaction. Conversely, visibility in one mempool does not ensure eventual confirmation.

Policy helps manage limited resources

Relay and mempool policy restrict what a node is willing to handle before confirmation. Consensus rules determine what blocks it accepts as valid. These layers overlap in purpose but are not identical. A transaction can fail a local policy check without proving that every possible block containing it would violate consensus. Exact behavior depends on implementation and version.

Diagnose with identifiers and context

For a fictional pending donation, collect the network, transaction identifier, observing node’s synchronization state and relevant policy response. Avoid exposing an entire wallet history when one transaction is sufficient. Compare observations with their timestamps. A responsible interface distinguishes not observed, rejected by this node, pending and confirmed instead of turning every missing lookup into failed payment.

When comparing two nodes, also record when each observation was made; their views can change while the comparison is underway.

Your turn / A paper experiment

Practice on paper

Explorer A shows a transaction pending; Explorer B has no record. List two explanations that do not require fraud.

I’ve tried it — show the worked answer

They may have different propagation timing or local policies, or one may be out of sync. The disagreement needs investigation of the same network and transaction, not an automatic resend.

Want to explore with buttons and instant feedback? Try the practice lab ↗

Think it through

Make a choice. Discover why.

Choose an answer and check the explanation. You can retry as often as you like. These are practice questions, not a test of mastery; answers are not saved or sent.

1. Is there one universal mempool shared identically by every node?
  • Yes
  • No
Read the explanation

No. Mempools are local views.

2. Is relay policy always identical to consensus validity?
  • Yes
  • No
Read the explanation

No. They answer different operational questions.

One idea to take with you

Describe a node’s observation without calling it the whole network.

Your learning, at your pace

Read every lesson freely. Optional progress tracking needs JavaScript and browser storage; it does not require an account or wallet.