Defining a Database Name Table › Planning › Mixed Page Groups and Maximum Records Per Page

Mixed Page Groups and Maximum Records Per Page

What Is Allowed?

SQL access to data in mixed page groups and with different maximum records per page is always allowed. However, by default, CA IDMS does not support the ability to access data in areas with different page groups or maximum records per page from a run unit. Therefore, if you need to access a database which exceeds the size limits of a single page group or which uses different record maximums from a single run unit, you must indicate this by specifying the MIXED PAGE GROUP BINDS ALLOWED option on the DBNAME statement that defines the database.

What Happens When Binding a Run Unit?

If an application program binds a run unit to a database that includes segments with a mix of page groups or maximum records per page, the bind may or may not succeed depending on the MIXED PAGE GROUP option specified on the database's DBNAME statement:

• MIXED PAGE GROUP BINDS ALLOWED—The bind will succeed regardless of what areas are included in the subschema.
• MIXED PAGE GROUP BINDS NOT ALLOWED—The bind will succeed only if all areas in the subschema are in the same page group and have the same maximum records per page.

Detecting Potential Problems

You can detect potential problems ahead of time by using the IDMSLOOK utility (or the LOOK system task). The DMCL option will warn you if you have mixed page groups or maximum records per page within any of your database names. The BIND option will indicate whether a bind run unit will succeed for a specified subschema and database.

To eliminate warning messages for database names created only for administrative convenience, you can designate them for utility use only.

Application Program Considerations

Special care must be taken in navigational-DML application programs that access data with a mix of page groups or maximum records per page. If the application program retrieves a record by dbkey then it must do one of the following:

• Specify on the DML command the name of the record that it is trying to retrieve
• Specify on the DML command the page group and maximum records per page of the record that it is trying to retrieve
• Ensure that the current page group and maximum records per page are correct for the record that it is trying to retrieve. The current page group and record maximum are those associated with the dbkey that is current of run unit.

Failure to take one of these actions may lead to the inability to retrieve any record or the retrieval of unintended records.

Identifying Potential Problem Programs

Numbered exit, Exit 34, is provided for use with the MIXED PAGE GROUP BINDS ALLOWED option. You can use this exit to help identify applications that may require modification to function correctly when mixed page group support is enabled.

Note: For more information about Exit 34, see the CA IDMS System Operations Guide.

Dictionary Considerations

MIXED PAGE GROUP BINDS ALLOWED cannot be specified for dictionaries. When defining a dictionary with a mixture of page groups or maximum records per page, the following rules must be observed:

• The DDLDML and DDLDCLOD areas must be in the same page group and have the same maximum records per page. The DDLDCMSG area (if included in the DBNAME) must also have the same page group and record maximum.
• The DDLCAT, DDLCATX, and DDLCATLOD areas must be in the same page group and have the same maximum records per page.
• These two area sets may be in different page groups.
• Dictionaries that share load areas must be in the same page group.

If you define a dictionary with a mixture of page groups or maximum records per page, certain utility functions such as UNLOAD can only be performed by segment or individual area, rather than for the dictionary as a whole.