Design guidelines for DEDBs

To define a data entry database (DEDB), you must determine the size of the CI and UOW, and follow design guidelines.

DEDB design guidelines
The following list describes guidelines for designing DEDBs.
DEDB area design guidelines
When designing a DEDB, be aware of the considerations and guidelines related to the DEDB area.
Determining the size of the CI
The choice of a CI size depends on several factors.
Determining the size of the UOW
The UOW is the unit of space allocation in which you specify the size of the root addressable and independent overflow parts.
SDEP CI preallocation and reporting
Because of data sharing, SDEP CIs cannot be allocated one at a time. Also, each data sharing system requires its own current CI. Therefore, a set of SDEP CIs are preallocated to each IMS on an allocation call.
Automatic management of Fast Path DEDB SDEP buffers
IMS can be configured to automatically clean up Fast Path DEDB sequential dependent segments (SDEPs) in online buffers by writing them to the physical database at intervals that you specify.
Processing option P (PROCOPT=P)
The PROCOPT=P option is specified during the PCB generation in the PCB statement or in the SENSEG statement for the root segment.
DEDB randomizing routine design
A DEDB randomizing module is required for placing root segments in a DEDB and for retrieving root segments from a DEDB.
Multiple copies of an area data set
The data in an area is in a VSAM data set called the area data set (ADS). Installations can create as many as seven copies of each ADS, making the data more available to application programs.
Record deactivation
If an error occurs while an application program is updating a DEDB, it is not necessary to stop the database or the area.
Physical child last pointers
The PCL pointer makes it possible to access the last physical child of a segment type directly from the physical parent. Using the INSERT rule LAST avoids the need to follow a potentially long physical child pointer chain.
Subset pointers
Subset pointers help you avoid unproductive get calls when you need to access the last part of a long segment chain.

Parent topic: Designing Fast Path databases

Related concepts

Data sharing in IMS environments