Fetch

Key Characteristics

• • Program Loading: Involves locating a load module (or program object) in a program library (e.g., STEPLIB, JOBLIB, LINKLIB, LPA) and loading it into the program's private virtual storage for execution.
  • Dynamic Nature: Programs can be fetched and released from memory as needed during execution, rather than being loaded solely at job initiation, optimizing memory usage and allowing for modular application design.
  • Database Retrieval: For relational databases like DB2, FETCH is an SQL statement used in conjunction with a cursor to retrieve the next row from a result set into designated host variables within the application program.
  • Sequential Access: Database FETCH operations typically retrieve data sequentially, row by row, after the cursor has been OPENed and before it is CLOSEd.
  • Error Handling: Both program FETCH (e.g., via LOAD macro or implicit CALL) and data FETCH (SQL FETCH) operations can return status codes or indicators (e.g., SQLCODE) signaling success, end-of-data, or various errors, which must be handled by the application.

Use Cases

• • Dynamic Program Invocation: A COBOL program using a CALL statement to invoke another program that is not statically linked, causing the called program's load module to be fetched into memory for execution.
  • Database Record Processing: An application program iterating through a result set from a DB2 query, using EXEC SQL FETCH CURSOR_NAME INTO :HOST_VAR1, :HOST_VAR2 END-EXEC to process each matching record sequentially.
  • CICS Program Control: A CICS transaction using EXEC CICS LINK PROGRAM('PROGNAME') or EXEC CICS XCTL PROGRAM('PROGNAME') to transfer control to another program, which implicitly involves fetching the target program's load module if it's not already in storage.
  • Assembler Program Loading: An assembler program explicitly using the LOAD macro to fetch a specific program or routine into memory for subsequent execution via CALL or BALR.
  • Sequential File Processing: While not explicitly called "fetch," reading the next record from a sequential file (e.g., using READ in COBOL) is conceptually a data retrieval operation.

Related Concepts