Change management

Performance management is really the management of change. Performance is stable if few changes occur in an IMS system.

More common is a continually changing environment where the IMS system must be adjusted to the addition of new application programs and respond to changes in:

• Application design
• Transaction volumes
• Database volumes
• Workload mix
• User population
• User priorities
• Volumes of non-IMS work
• Hardware configuration

IMS tuning attempts to allocate resources for efficient transaction processing.

You can use various techniques to tune the system during operation. For example, you can:

• Start new message regions
• Change transaction PARLIM, PROCLIM, or class assignments
• Alter message region class assignments

These activities involve ensuring that sufficient IMS resources, such as regions, pool space, or control block areas, are provided. The IMS configuration needs to be matched to the installation's physical resource constraints. Typically, the use of virtual storage is exchanged for some I/O activity controlled by IMS, and contention is reduced for data stored on DASD devices. Tuning should not be crisis management but a continual compensation for changes or workload trends.

A systematic approach to tuning is included in Identifying and correcting performance problems.