OpenEdge Getting Started:<br />Database Essentials Using PROBKUP versus operating system utilities

Among knowledgeable administrators, there are debates concerning the use of the OpenEdge PROBKUP utility versus operating system utilities. Also, there is a great deal of misinformation about when and how to back up a system while leaving it online. This section discusses these issues in detail.

Understanding the PROBKUP utility

The OpenEdge PROBKUP utility was created to back up databases. It has many nice features that make it unique, including:

The PROBKUP utility is database-aware.

Database aware means that the utility understands the structure and format of the database. PROBKUP can scan each block to ensure it is the proper format during the backup process. It takes longer to do this scan, but the added integrity checking of potentially seldom-used blocks is worth the small performance degradation.

PROBKUP has an online option.

This online option allows you to back up a database while the database is available to users. Since PROBKUP is database-aware, it knows when the structure of the database changes regardless of the number of disks/areas/extents. Therefore, the syntax of the command does not need to change when the structure of the database changes.

How PROBKUP works

Establish a database latch (online only).

Do a pseudo checkpoint (online only).

Switch AI files (if applicable).

Back up the primary recovery area (online only).

Release the database latch (online only).

Back up the database.

The database is backed up from the high-water marks downward. Free blocks are compressed to save space. Online backups represent the database at the time the backup started. All transactions started after the backup has begun will not be in the database when a restore and transaction rollback occurs.

The reason for the pseudo checkpoint in an online backup is to synchronize memory with disk prior to backing up the database. This synchronization is critical since the PROBKUP utility can then back up all of the data that is in the database or in memory at that moment. Other utilities can only back up the information on disk, thus missing all of the “in memory” information.

Adding operating system utilities to augment PROBKUP

The PROBKUP utility backs up the database and primary recovery area. This utility does not back up the after-image files or even the database log file.

All complete backup strategies use operating system utilities to back up additional important files on the system such as programs, application support files, and user home directories. Some administrators choose to back up their database to disk with PROBKUP and use an operating system utility to augment the database backup with other files to get a complete backup on one archive set. Also, you should back up your after-image files to separate media from the database and before-image files to increase protection, as discussed in the "After-imaging implementation and maintenance" section.