Rollback and before-images¶

Edition: Community and Enterprise

Every fix can be undone, and undoing it exposes no more data than the fix did.

The before-image¶

Right before a fix changes anything, the executor reads the rows the statements will change, in the same transaction, with the same bound values, and locks them. That copy is the before-image. The executor seals it to its own key, like the values, and stores it with the execution.

A before-image holds each row's key and the columns that change (whole rows for a DELETE). It can hold more customer data than the values themselves, which is why it is sealed too.

A table without a primary or unique key

Without a key, sealfix cannot tell which row to restore. Check W1 warns the DBA reviewer: such a fix cannot be rolled back.

A rollback is a request¶

flowchart LR
    F["Executed fix"] -->|"Request rollback, with a reason"| RB["Rollback request<br/>built from the sealed before-image"]
    RB --> DR["Dry run"] --> AP["Same approvals<br/>as any fix"] --> EX["Executor restores the rows"]
    EX --> RF["Original fix shows<br/>Rolled back"]
    classDef box fill:#E9EEF6,stroke:#23407A,color:#13202D
    class F,RB,DR,AP,EX,RF box

The requester of an executed fix asks for the rollback, with a reason.
The rollback has its own dry run and needs the same approvals. Its page shows how many rows the before-image holds, never what they contain, to anyone, the requester included.
If the rows changed since the fix ran, the rollback is refused at its dry run and again at execution, so it never overwrites someone else's later change.
Only one rollback of a fix can be open at a time.

Triggers and side effects¶

A trigger can change other tables, or reach outside the database, when the fix runs. A rollback restores the fix's own rows only. That is why the dry run lists every trigger the fix fires, and the requester decides per trigger: let it run, or (where the policy allows it) disable it inside the transaction. A trigger with effects outside the database is always refused.