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Database Administration
Protecting Your Data : Recovering a Database : Sample recovery plans : Example 4: high availability requirements
 
Example 4: high availability requirements
The database administrators at site D have determined the following availability requirements. The table below provides examples.
Table 23. Sample high availability requirements
Availability question
Answer
Recovery technique
How many committed transactions can you afford to lose?
None
Enable after-imaging.
How long can the application be offline while you perform scheduled maintenance?
Never
Perform online backups with after-image files.
How long can you spend recovering if the database becomes unavailable?
4 hours
Keep a duplicate system on warm standby. Use roll-forward recovery to keep the standby database current with the production database.
Must distributed transactions occur consistently across databases?
No
Do not implement two-phase commit.
Given these high availability requirements, the database administrators keep a duplicate database on warm standby, and follow these steps:
1. Restore a backup of the production database to an empty database with a duplicate structure on a different system.
2. On the production database, enable after-imaging using AI files with fixed-length extents.
3. On the production database, whenever a fixed-length AI extent becomes full, copy it to the standby system and roll it forward on the standby database.
4. After bringing the standby database up to date, mark the full after-image extent on the production database as empty to make it available for reuse.
In addition, backups and AI files are constantly tested and verified on the standby database. The standby database is put through crash recovery, verified, and if possible, backed up before restoring online backups of the production database to the standby database.