State Recovery

[threewebcode]

There is one command named rollback in the command line which can be used in some cases. In the layer one node, there are two major states: network state and application state. The network state contains block state and current world state. The application state is derived from the ABCI application. To some extent, the application is one part of the whole global world state.

The network is alive and safe if theses states are consistent. If state differences appear, some measures should be taken to recovery the network. The rollback command is one of the measures available.

The anatomy of rollback command:

1. The block state and world state are stored in the database and can be loaded from the file system.
2. Compare the height between the block state and world state
3. Suppose the block is finalized, the world state is invalid
4. Overwrite the world state with last height.

As far as i know, the block is persisted firstly, then the transactions in the block are executed and committed into the application state. The world state is stored at the last step. The headache issue is the state inconsistency between the application state and world state. The codes of application modules should be examined and tested carefully.