Progress
Database Administration
Guide and Reference
Storage Areas
Storage areas consist of one or more extents and are the largest physical units of a database. With storage areas, you have physical control over the location of database objects: you can place each database object in its own storage area, place many database objects in a single storage area, and place objects of different types in the same storage area. See "Administrative Planning," for information on managing storage areas. Though you can extend a table or index across multiple extents, you cannot split them across storage areas.
Certain storage areas have restrictions on the types of extents they support. The transaction log storage area, used for two-phase commit, uses only fixed-length extents but can use more than one. The other storage areas can use many extents but only one variable-length extent, which must be the last extent.
Storage areas are identified by their names. The number and type of storage areas used varies from database to database; however, all Progress databases must contain a control area, a schema area, and a primary recovery area. These three mandatory storage areas are detailed below, along with the optional areas.
Control Area
The control area contains only one variable-length extent: the database structure extent, which is a binary file with a .db extension. The .db file contains the _area table and the _area-extent table, which list the name of every area in the database, as well as the location and size of each extent.
Schema Area
The schema area can contain as many fixed-length extents as needed; however, every schema area should have a variable-length extent as its last extent. The schema area stores all database system and user information, and any objects not assigned to another area. If you choose not to create any optional application data areas, the schema area contains all of the database’s objects and sequences.
Primary Recovery Area
The primary recovery area can contain as many fixed-length extents as needed, as long as the last extent is of variable length. The primary recovery area is also called the before-image area because the .bn files of its extents record data changes. In the event of a hardware failure, the Progress Restore (PROREST) utility uses the contents of the .bn files to restore the database.
Application Data Area
The application data storage area contains all application-related database objects. Defining more than one application data area allows you to improve database performance by storing different objects on different disks. Each application data area contains one or more extents with a .dn extension.
Transaction Log Area
The transaction log area is required if two-phase commit is used. This area contains one or more fixed-length extents with the .tn filename extension; variable-length extents are not allowed. See "Using Two-phase Commit," for more information about the transaction log area.
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