PDAB—Construct a parallel data access block (QSAM)

The PDAB macro is used with the GET (TYPE=P) macro. It defines an area in the problem program where the open and close routines build and maintain a queue of DCB addresses for use by the get routine.

The parallel data access block is constructed during the assembly of the problem program. MAXDCB must be coded in the PDAB macro, because it cannot be supplied from any other source.

Certain data set characteristics prevent a DCB address from being available on the queue—see the description of QSAM parallel input processing in z/OS DFSMS Using Data Sets.

Restriction: Do not use the PDAB macro if a QSAM GET will be used in 31-bit addressing mode.

UNIX files: OPEN ignores the PDAB for a DCB that is for a UNIX file or subsystem data set.

The format of the PDAB macro is:

MAXDCB=absexp (maximum value is 32767 bytes)

specifies the maximum number of DCBs that you require in the queue for a GET request.

The number of bytes required for PDAB is equal to 24+8n, where n is the value of the keyword, MAXDCB.