How Datacom VSAM Transparency Works with Online Processing

Learn how Datacom VSAM Transparency works with online processing.

Startup Processing

  1. If DVVMTPR is listed in the Program List Table (PLT),
    Datacom VSAM Transparency
    is automatically activated at CICS startup.
    If
    Datacom VSAM Transparency
    is subsequently shut down manually through the
    DVMT DEACT=$CAVT
    command, the
    DVMT ACT=$CAVT
    command is required to reactivate
    Datacom VSAM Transparency
    .
  2. As each module and table is loaded, its release level is verified. DVVXTPR and DVVXPPR must be synchronized. If a discrepancy is encountered, the name(s) of the modules or tables loaded at an incompatible level are displayed on the terminal and processing is terminated pending correction.
  3. For each VSAM file listed with
    VSAMNM=
    in the Online VSAM Interface Table (DVVXTPR), places the file under Transparency control unless it is already opened for native VSAM access.

Pre-MUF Request Handling

  1. The Transparency Online Request Interceptor intercepts each request to the CICS File Control Program (DFHFCP) in a CICS Global User Exit (GLUE) to determine whether it is for a file which is under Transparency control.
  2. If the request is to a file which is not under Transparency control, the Transparency passes the request on to the CICS File Control Program (DFHFCP) which handles it just as it did before installing
    Datacom VSAM Transparency
    or when
    Datacom VSAM Transparency
    is not active.
  3. If the request is to a file which is under Transparency control, the following processing occurs:
    1. The Transparency retrieves the "VSAM file to
      Datacom/DB
      table mapping information" from the Online VSAM Interface Table (DVVXTPR), translates the VSAM request to the corresponding
      Datacom/DB
      request, and passes the request to the
      Datacom CICS Services
      .
    2. Datacom CICS Services
      selects a User Requirements Table for processing the specified table and passes the request to the
      Datacom/DB
      Interface (DBINFPR), which passes it to the MUF.

Post-MUF Request Handling

After the MUF processes the request and sends the
Datacom/DB
return code and data to
Datacom VSAM Transparency
using
Datacom CICS Services
:
  • Datacom VSAM Transparency
    translates the return code to the corresponding VSAM feedback code
  • Returns it and the data to the application

Abend Processing

When a critical error occurs,
Datacom VSAM Transparency
produces an abend code. See the Online Abend Codes table for a description of each code and when it would be generated. If TXNUNDO=YES is specified in the online User Requirements Table, the active transaction is backed out to the last sync point.

Shutdown Processing

Typically,
Datacom VSAM Transparency
is deactivated automatically during CICS shutdown which occurs at PLT shutdown. However, you can deactivate
Datacom VSAM Transparency
manually using the
DVMT DEACT=$CAVT
command. When deactivated, either automatically or manually, the Transparency marks all files under its control as closed. When files are closed in this way, no more requests can be executed through the Transparency until a subsequent activation is performed. If the VSAM file exists and the CICS job stream contains JCL for executing the application in native mode, native VSAM processing resumes if you issue the CEMT OPEN command.