BAC-L2-SUB-109Substrate / Polkadot SDK
Events, errors and block hooks
What the chain tells the outside world, and what it executes automatically each block — the part of the runtime nobody triggers.
- Level
- L2 — Appchain developer
- Duration
- 4 h
- Maintainer
- Polkadot / Substrate Lead Architect
Learning objectives
- 01Emit events an indexer can actually consume
- 02Distinguish a business error from a dispatch failure
- 03Use begin- and end-of-block hooks without endangering the chain
Guided lab
Add a periodic task via a hook and observe its effect on block production time.
Independent lab
Make the periodic task bounded and resumable, then show it never exceeds its budget.
Security angle
An unbounded hook halts the chain: build the evidence that yours will not.
Assessment
Bounded periodic task, demonstrated by a load test.