Module backup 

Pre-migration backup for destructive steps.

DropColumn has no inverse step, so a plan containing drops can only be rolled back from a backup taken before execution. When the caller supplies a backup directory, the executor snapshots the affected rows first and rollback restores from that snapshot instead of failing outright.

Functions

restore_backup

Restore a destructive plan from its backup. Returns None when no backup file exists for the plan.

write_backup

Snapshot rows touched by destructive steps. Returns the row count.