Program modification requirements for DDM

 

Remote files can be accessed by iSeries™ application programs written in the HLL and control language.

In most cases, these applications can access both local or remote files without the programs being changed. However, some considerations and restrictions might require the programs to be changed and recompiled. These are grouped in three categories:

• iSeries functions that are not supported by the DDM architecture, but for which a System/38™ extension to the architecture might exist. These functions can be used only when the source and target servers are System/38s or iSeries servers.

• Restrictions and considerations that apply when the source or target server is an iSeries server.

• Restrictions and considerations that apply to all target servers (iSeries servers and non-iSeries servers). User programs accessing local files should program for abnormal conditions such as No record found, End of file, and Record lock time-out on read for update. These conditions can also occur when a remote file is being accessed using DDM. In addition, the use of DDM exposes the program to communication line failures while sending disk I/O operations.

  When a communications failure occurs, the server sends an appropriate message to the job, which is returned to the application program as a generic file error. Each high-level language provides unique user syntax capabilities for user-controlled handling or default processing of exceptional results of a disk operation. Some languages might permit the user to retrieve the job message identification (ID) that would specifically indicate a DDM communications failure. Refer to the appropriate language manual for specific capabilities.

  For secondary SDLC lines, it is recommended that the INACTTMR parameter of the Create Line Description (SDLC) (CRTLINSDLC) command be set on the source and target servers to detect the stopping of polling by the primary server. This prevents the possibility of a DDM read-for-update record lock lasting indefinitely due to a communications failure on the primary server.

• DDM architecture-related restrictions
  The items listed in this topic are DDM architecture-related restrictions. Therefore, application programs that use these items might have to be changed and recompiled before they can access remote files.

• iSeries source and target restrictions and considerations for DDM
  When the source server is an iSeries server, iSeries database functions can be used on remote files. There are some restrictions, however.

• Non-iSeries target restrictions and considerations for DDM
  In addition to the restrictions that apply when the target server is an iSeries server, the restrictions in this topic also might apply when the target server is not an iSeries server or a System/38.

 

Parent topic:

Prepare to use DDM