The runtime of a Substrate blockchain acts as the state transition function, where all of the business logic of our chain lives. A runtime typically contains a number of pallets that, together, define the business logic of the chain. Each pallet alone provides ways for accounts and other pallets to interact with them. Pallets are written in FRAME, Substrate's opiniated framework for writing runtimes. Two key libraries that make it possible to write a pallet using FRAME are:
frame_system: provides all core system functionalities for integrating a pallet into a runtime and enabling pallets to interact with eachother.frame_support: provides a pallet with a way to create dispatchable calls, storage capabilities, events and errors and core utilities.
As runtime engineers, a pallet provides you a way to:
- Specify storage items for your blockchain
- Specify some callable functions for your blockchain
- Emit events and errors
- Specify some custom logic for callable functions
- Generate metadata
This gives you a lot of flexibility for the logic you're writing, but this means you have a lot of responsibility for carefully handling errors.
Important concepts:
- Weights
- Verify first, write last
- Storage read/write efficiency
- Error handling