For the DRDA code to be used on the VSE application server the following conditions must be met:
The recommended supervisor modes for operation are the ESA mode or the VMESA mode. DRDA support is not provided with the VSE Guest Sharing function.
For the DRDA code to be used on the VSE application requester the following conditions must be met:
CICS/VSE online application programs and VSE batch application programs have the ability to execute SQL statements to access and manipulate data managed by any remote application server that implements the DRDA architecture. The SQL statements in these application programs can be static, dynamic, and extended dynamic, even if the target system does not support extended dynamic statements.
| Note: | Application programs accessing a local AS (or a VM database via guest sharing) will always use Private protocol. |
Application programs use the facilities of an accessible DB2 Server for VSE Online Resource Adapter, running in the same partition as the application and acting as a DRDA application requester, to route SQL requests to a DRDA application server. This is illustrated in Figure 121.
Figure 121. Online DRDA Application Requester (AR) Support
*-----------*
*--------------*----* | DRDA |
| CICS APPL'N | AR *----------------->| REMOTE |
*--------------*----* | AS |
*-----------*
|
The batch application programs use the facilities of the Batch Resource Adapter which executes in the same partition as the batch application program. The batch application requester is loaded into the partition when the first SQL request is issued by the application program.
The Online Resource Adapter establishes communication links to local application servers at initialization time and maintains these links. CICS applications accessing the local application servers use these links. For remote application servers, the Online Resource Adapter does not establish any communication links at initialization time. Instead, the Online Resource Adapter acquires a session to the remote system where the remote server runs when the application program first connects to the remote server. The session is freed when either:
The Batch Resource Adapter establishes communication links to local or remote application servers as needed. These links are freed from either:
An application program can access only one application server (remote or local) in a single unit of work (LUW). A COMMIT RELEASE or ROLLBACK RELEASE must be issued to terminate the LUW before an attempt is made to connect to another application server.
In addition to the remote server it is updating, a CICS/VSE application program can, within the same unit of work, update another CICS resource which participates in two-phase commit processng. Note that VSAM does not participate in two-phase commit processing. In this case, the user executing the program must specify a value of 2 for the SQLGLOB parameter SYNCPOINT. The CICS/VSE syncpoint manager establishes a protected conversation with the remote server and the CICS/VSE syncpoint manager ensures that updates made to the remote server and these other CICS resources are synchronized. Note that to the remote remote DRDA application server this connection looks like a DRDA 2 connection. However theCICS/VSE application is still limited to accessing a single DRDA server within one LUW. That is, the CICS/VSE application is not able to use CONNECT (Type 2) connections as defined in the IBM SQL Reference, Version 2, Volume 1.
Batch applications always use single phase commits (SYNCPOINT 1).