Chapter 2 · Mechanics · lesson 3
The life of a transaction
9 min
Builds on Blocks and the chain
Chapter 2 · Mechanics · lesson 3
9 min
Builds on Blocks and the chain
You press a button in a wallet. Somewhere between there and "done" are five distinct states, and almost every confusing thing about using a blockchain happens in the gaps between them.
Your wallet builds the transaction — recipient, amount, fee, and a nonce counting how many transactions this account has sent — then signs it with your private key.
Nothing has left your machine yet. A signed transaction is just a file.
This account nonce is unrelated to the mining nonce from track 0. Same word, different job: this one puts your transactions in order and stops the same signed transaction being replayed twice.
It is also why transactions from one account cannot overtake each other. Nonce 7 cannot be processed before nonce 6, no matter what you pay.
The wallet sends it to a node, which checks it is well-formed and gossips it to its peers. Within a second or two most of the network is holding a copy.
It now sits in the mempool — waiting, visible to everyone, not yet real.
Predict
A validator picks it up and puts it in a block. Your wallet goes green.
This is the moment most people call "done". It is not, quite — and the next lesson explains why.
After a couple of epochs, roughly thirteen minutes on Ethereum, the transaction becomes finalised: undoing it would require an attacker to destroy an enormous amount of staked ETH.
That is as permanent as anything gets.
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