Server program structure

The commit scope within the z/OS® application environment is all the work under the TCB from which the commit request is made to z/OS Resource Recovery Services (RRS). Server environments, therefore, need a separate TCB under which the individual client requests will be managed. Each TCB will map to a PST for thread handling.

The following figure shows an example TCB structure for a server environment.

Figure 1. DRA uses one TCB per thread
Begin figure description. DFSCDLI0 loaded with the TCB in 0S/390 Application Region. PST in IMS Database Manager. Three TCBs mapped individually to three PSTs in IMS DB manager through the DRA. End figure description.

Each connection to an IMS DB uses a thread under the TCB. When the APSB call is processed, a context is established and tied to the TCB. At commit time, all contexts for this TCB are committed or aborted by RRS.

Loading DFSCDLI0 rather than link editing is attractive when the z/OS application region is a server supporting many clients with many instances of threads connected with the IMS DBs.