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 we can verify that the change has already been written to disk, i.e.:
- 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) ³ LSN.