Rollback

Warp Sync detects a reorganization when it receives a block from the server that has a previous hash different from the hash of the latest block it has.

This means the server has switched over to a different sequence of blocks.

As explained in the page about Reorganization, the wallet must rollback to a common previous state but we don’t exactly know when we deviated. Besides, we cannot rollback any number of blocks because we can apply blocks but we cannot undo a block.

However, we have checkpoints and we can revert to a previous one.

Revert to Checkpoint

Every row from the blocks, transaction, received notes and witnesses table have a height value that indicates when the data was obtained. To rollback to the state after block H, we just have to delete every row that has a height greater than H.

And to undo the spends that happened after H, we also need to reset the spent field of any notes if the spent height is greater than H.