Progress
Database Administration
Guide and Reference


Example 2: Moderate Availability Requirements

The database administrators at site B have determined the following availability requirements. Table 8–2 provides examples.

Table 8–2: Sample Moderate Availability Requirements 
Question
Answer
Recovery Technique
How many committed transactions can you afford to lose?
1 day of transactions
Perform daily backups.
How long can the application be offline while you perform scheduled maintenance?
8 hours per week
Perform weekly offline backups with daily online full or incremental backups.
How long can you spend recovering if the database becomes unavailable?
8 hours
Keep a full backup and one incremental or AI file.
Must distributed transactions occur consistently across databases?
No
Do not implement two-phase commit.

Given these requirements, the database administrators perform a full offline backup every Saturday night. Because they can lose only one day of transactions, they supplement weekly backups with daily online incremental backups. Because they can only allow time to restore a single incremental, they perform incremental backups with an overlap factor of six. This means that each incremental backup saves changes that were saved in the last six incremental backups. The full backup is tested Saturday night, and after the incremental backups finish they are tested using disk space reserved for that purpose.


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