Interactive file processing with DDM

 

Consider these items when using interactive file processing with DDM.

• The greater the number of random file operations per unit of performance measurement, the greater the difference between local and remote file processing because each operation has to be sent separately across the communications line. DDM cannot anticipate the next operation.

  Using a simple inquiry application that produces display output, by using workstation subfile support (as an example), consider an application that does two random record retrievals per Enter key versus one that does 15 random record retrievals. The operator might barely notice a delay in response time when two records are retrieved. However, there would be a noticeable difference between local and remote response time when 15 records are retrieved randomly from the remote server.

• Use of display station pass-through should be considered when the amount of data transferred back to the local (source) server per unit of performance measurement significantly exceeds the amount of data presented on the display. Test results have shown that the total elapsed time between a single deblocked DDM get record operation and an equivalent user-written APPC operation is very close, with APPC being slightly quicker. The DDM operation does require more processing seconds than the direct APPC interface.

  Also, because each DDM operation always requires an operation result response from the remote server to ensure data integrity, user-designed partner APPC programs can offer an advantage for update, add, and delete operations by not validating the result of the operation until a later time.

• Be aware that additional time is needed when accessing files on other servers, particularly the time required for communications over the line. This should be considered when determining whether the file should be a local or remote file, especially if it is to be used often.

 

Parent topic:

Performance considerations for DDM