Implementing Siebel Business Applications on DB2 UDB for z/OS > Customizing a Development Environment > Siebel Tools Considerations on DB2 for z/OS >

About Reducing VARCHAR Field Lengths

DB2 for z/OS pads VARCHAR fields to their maximum lengths in indexes. To increase flexibility, Siebel applications make extensive use of VARCHAR columns. This use of VARCHAR columns can cause performance degradation for z/OS customers who have a large number of rows in certain tables, such as S_CONTACT.

The total length of an index equals the combined lengths of all index columns. To reduce the index length, you reduce the length of participating columns. To make better use of index space, users of DB2 for z/OS can reduce VARCHAR lengths, in cases where there is no application impact, using Siebel Tools.

Analyze your business needs at installation or upgrade to determine whether it is necessary to reduce VARCHAR field lengths. Some examples are the following:

• FST_NAME and LAST_NAME, VARCHAR(50) columns in S_CONTACT. These belong to many indexes.
• ADDR, a VARCHAR(200) column in S_ADDR_PER.
• NAME, a VARCHAR(100) column in S_ORG_EXT.

Be aware that you also must make the same length reductions to columns denormalized from those you have reduced. One example is S_PER_RESP.PER_FST_NAME, which is denormalized from S_CONTACT.FST_NAME.

A denormalized column duplicates the data in a column in another (base) table for performance reasons. The table and column names of the duplicated column are specified in the Denormalization Path property of the Column object definition of the denormalized column. For more information on columns, see Using Siebel Tools.