These topics describe the file processing parameters and other methods or considerations that can affect database file processing.
Before a file is opened for processing, you need to consider how you want to use the file in the program or job. A better understanding of the runtime file processing parameters can help you avoid unexpected results and improve the performance of your program. The parameter values are determined by the high-level language program, the file attributes, and any open or override commands processed before the high-level language program is called.
When a file is opened, the attributes in the database file description are merged with the parameters in the program. Normally, most of the information the system needs for your program to open and process the file is found in the file attributes and in the application program itself.
Sometimes, however, it is necessary to override the processing parameters found in the file and in the program. For example, if you want to process a member of the file other than the first member, you need to tell the system to use the member you want to process. The Override with Database File (OVRDBF) command allows you to do this. The OVRDBF command also allows you to specify processing parameters that can improve the performance of your job, but that cannot be specified in the file attributes or in the program. The OVRDBF command parameters take precedence over the file and program attributes.