Determining the Size of the Database › Sizing a Megabase › Assigning Segments to Page Groups

Assigning Segments to Page Groups

By assigning segments to page groups, you can maintain, under a single central version, multiple databases that total more than a billion pages. A page group uniquely identifies a collection of page ranges. You can specify a numeric identifier in the range 0 through 32,767 as a page group.

More Information

For more information on varying the db-key and page groups, see the CA IDMS Database Administration Guide.

Considerations

Although segments can be assigned different page groups and database key formats, the following restrictions apply:

• By default, a single database transaction can access data in only one page group for a non-SQL-defined database. Therefore, data to be accessed together must be defined within the same page group.
• The single page group restriction for a transaction does not apply to SQL-defined databases or to non-SQL-defined databases accessed through a DBNAME with Mixed Page Group Binds Allowed. However, all records of a record type to be accessed in a single transaction must reside in the same segment. While you can horizontally segment a database, for example by placing customer information in three segments (CUSTEAST, CUSTWEST, CUSTCENT), you can access only one of these segments at a time from within a transaction.
• For non-SQL defined tables, owner and member records for a chain set must be in the same page group and have the same number of records per page.
• For SQL defined tables, referenced and referencing tables for a referential constraint must be in the same page group and have the same number of records per page, and a table and its index area must be in the same page group and have the same number of records per page.
• By default all segments accessed by a single database transaction must have the same database key format. However, when using a DBNAME with Mixed Page Group Binds Allowed, a single transaction can access data from multiple page groups, each having a different database key format.
• All segments of a dictionary must be in the same page group.

More Information

For more information on the use of Mixed Page Group Binds Allowed, see the CA IDMS Database Administration Guide.