14.2.1 Determining the segment size

We normally recommend an RDAREA segment size of about one-tenth the RDAREA storage page count. The segment size will be less than one-tenth for large RDAREAs, however, since the maximum segment size is 16,000 pages. This subsection describes the implications of segment size and considerations that should be taken into account when the segment size is selected.

Organization of this subsection
(1) Selecting a large segment size
(2) Selecting a small segment size
(3) Setting procedure

(1) Selecting a large segment size

Improved performance
Note:
  • The number of tables and indexes that can be stored per user RDAREA is reduced because the number of segments per RDAREA is reduced.

(2) Selecting a small segment size

Reduction in required disk space
  • The number of unused pages can be reduced because many tables, each containing a small amount of data, can be stored in one user RDAREA.
Notes
  • If a large amount of data is added to a user RDAREA that is based on a small segment size, the segment allocations count increases, thereby increasing overhead.
  • Because the number of segments increases, the amount of locked resources also increases when a table is deleted or all rows are deleted from a table.

The following figure provides an overview of user RDAREAs depending on segment size.

Figure 14-1 Overview of RDAREAs depending on segment size

[Figure]

(3) Setting procedure

The create rdarea statement of the database initialization utility (pdinit) or the database structure modification utility (pdmod) is used to set the segment size.