Database file processing: Runtime considerations

 

Before a database file is opened for processing, 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.

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, 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.

These topics describe the file processing parameters and other methods or considerations that can be used to affect database file processing. 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.

• File and member name
  Before you can process data in a database file, identify which file and member you want to use with the FILE and MBR parameters.

• File processing options
  DB2 Universal Database for iSeries provides several runtime file processing options.

• Data recovery and integrity
  You can specify several file processing parameters for data recovery and integrity.

• Locking shared data
  By definition, all database files can be used by many users at the same time. However, some operations can lock files, members, or records to prevent them from being shared across jobs.

• Sharing database files in the same job or activation group
  By default, the database management system allows one file to be read and changed by many users at the same time. You can also share a file in the same job or activation group by specifying the SHARE parameter.

• Sequential-only processing of database files
  If your program processes a database file sequentially for input only or output only, you might be able to improve performance by specifying the sequential-only processing (SEQONLY) parameter on the Override with Database File (OVRDBF) or the Open Database File (OPNDBF) command.

• Summary of runtime considerations for processing database files
  These tables show whether you can specify a particular file processing option on a CL command and in a high-level language.

• Storage pool paging option effect on database performance
  The paging option of shared pools can have a significant impact on the performance of reading and changing database files.

 

Parent topic:

Processing database files

 

Related concepts

ILE Concepts PDF
Control language

 

Related reference

Create Physical File (CRTPF) command
Create Logical File (CRTLF) command
Create Source Physical File (CRTSRCPF) command
Add Physical File Member (ADDPFM) command
Add Logical File Member (ADDLFM) command
Change Physical File (CHGPF) command
Change Physical File Member (CHGPFM) command
Change Logical File (CHGLF) command
Change Logical File Member (CHGLFM) command
Change Source Physical File (CHGSRCPF) command
Override with Database File (OVRDBF) command
Open Database File (OPNDBF) command
Open Query File (OPNQRYF) command
Close File (CLOF) command