State Pruning and Expiry

What Lives in Blockchain State

A blockchain's 'state' is everything you need to know to validate the next block: account balances, contract storage, nonces, code. The state grows every time someone deploys a contract, creates an NFT, or writes data on-chain. Over time, it just keeps getting bigger — because old data doesn't naturally get removed. Ethereum's full state is hundreds of gigabytes; the full historical archive (everything since genesis) is multiple terabytes.

Three Kinds of Nodes

Not every node stores everything. **Archive nodes** store the full historical state at every block — useful for analytics, but huge (multiple TB on Ethereum). **Full nodes** store the current state and recent history but prune older history — most validators run these (~1.5 TB on Ethereum mainnet). **Light nodes** store almost nothing, just block headers, and ask full nodes for any specific data they need. The trade-off is storage vs trust.

Why This Is a Problem

If running a node requires expensive hardware, fewer people will run them, and the network becomes more centralised. Ethereum is already at the edge of what comfortable home setups can run — a $2000 PC can do it but barely. The community is working on solutions to keep this from getting worse, including state pruning (delete what we can), state expiry (push old state off the main path), and Verkle trees (smaller cryptographic proofs).

• Archive node: full history, multiple TB — for analytics and explorers
• Full node: current state + recent history, ~1.5 TB on Ethereum — for validators
• Light node: just headers, asks others for data — for phones and lightweight clients
• The growth problem: state never shrinks naturally; eventually nodes get too expensive