Archiving (cont’d)
To archive the log, use 2 pairs of shadowed disks. Dump one pair to archive (e.g. tape) while using the other pair for on-line logging. (I.e. ping-pong to avoid disk contention)
- Optimization - only archive committed pages and purge undo information from log before archiving
To do incremental archive, use an archive bit in each page.
- Each page update sets the bit.
- Archive only copies pages with the bit set, and clears it.
To reduce media recovery time
- rebuild archive from incremental copies
- partition log to enable fast recovery of a few corrupted pages