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Flashback Logs
FLASHBACK DATABASE uses flashback logs
Logs contain changed blocks
Automatic and ongoing creation of new logs
- Tune for best performance
- Undocumented parameters help?
Written to Flash Recovery Area
Transactions dictate frequency / size of logs
Automatic deletion of obsolete logs
Notes:
Flashback logs are written to the flash recovery area if the database is configured for flashback database support. (We will see how to do that next.) The logs contain changed blocks. The flashback logs are different from redo logs and undo – they are a separate, optional recording of database activity.
The transaction rate on your database will have an affect on the performance of creating the logs and the number and size of the logs. Oracle says the overhead of enabling flashback database is “comparatively limited”. Refer to chapter 5 of the Oracle Database Backup and Recovery Basics manual for tuning tips. I’ll summarize them here:
Use fast disks for the flash recovery area
Avoid file system caching. Use ASM if possible (refer to the Automatic Storage Management lesson of this course for more information on ASM).
Use striped storage volumes, with a small (128k) stripe size (using ASM provides this).
Logs are automatically deleted when:
The flash recovery area becomes constrained (i.e. runs out of free space) and:
The log is not needed for a recovery within the window specified in the DB_FLASHBACK_RETENTION_TARGET parameter.
Notes for this slide continue on the next page…