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This topic describes how LONG columns in the Siebel Schema are implemented on the DB2 for z/OS platform. Siebel Business Applications use LONG columns on RDBMS tables to store arbitrarily long character data up to 16,350 characters. Examples include scripts, emails, notes, and descriptions. On all RDBMS platforms, except DB2 for z/OS, the size of LONG columns is fixed and is independent of the size of the table space in which the table is defined.
On the z/OS platform, a LONG column in the logical Siebel Schema is indicated as a LONG VARCHAR column in the Siebel Repository. As of DB2 Version 9.1 for z/OS, LONG VARCHAR columns cannot be created with the LONG attribute in the DB2 catalog. Instead DB2 for z/OS creates these columns as VARCHAR columns that are set to the maximum size possible. The size of these VARCHAR columns varies according to two factors:
You can estimate the size of the LONG column by calculating the buffer pool size of the table space minus the size of all other columns; the LONG column takes up the remainder of the buffer pool size defined for the table space. For example, a table containing one LONG column, defined in a 16-KB table space, with a combined byte size for all other columns of 5 KB, results in the creation of a VARCHAR column having a size of about 11 KB. For more information on calculating the size of columns, refer to the vendor documentation on the IBM Web site.
The Siebel dbchck utility compares the physical database schema with its logical definition in the Siebel Repository and generates errors for any inconsistencies between them. However, the dbchck utility does not generate errors for LONG columns, which are identified as LONG VARCHAR columns in the Siebel Repository and physically created by DB2 as VARCHAR columns, because inconsistencies between the logical and physical definitions of these columns is expected behavior on the DB2 for z/OS platform.
When you run other Siebel utilities, for example, Synchronize Schema Definition (ddlsync), the utilities generate LONG DDL syntax for these LONG columns if the tables containing the columns need to be re-created. However, when the table is re-created, the LONG syntax is converted by DB2 and the column is again physically created as a VARCHAR column set to the maximum size possible.
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