Recovery: The REDO Phase
We repeat History to reconstruct state at crash:
- Reapply all updates (even of aborted Xacts!), redo CLRs.
Scan forward from log rec containing smallest recLSN in D.P.T. For each CLR or update log rec LSN, REDO the action unless:
- Affected page is not in the Dirty Page Table, or
- Affected page is in D.P.T., but has recLSN > LSN, or
- pageLSN (in DB) ??LSN.
To REDO an action:
- Reapply logged action.
- Set pageLSN to LSN. No additional logging!