Essentially everything that was said about UPAM also applies to the access method FASTPAM.
However you should bear in mind the following restrictions:
The file format must be NK4
(BLKCTRL=NO, block size=multiple of 4 KB).All accesses are made via absolute block numbers.
There are no synchronization mechanisms when two or more users access the same file.
FASTPAM supports multisystem networks by means of shared pubsets, but not remote file access (RFA).
FASTPAM provides better performance than UPAM because FASTPAM does not run the initialization and validation routines required for I/O operations prior to each I/O, but only once, before the file is opened.
Before the OPEN, the user defines a system environment consisting of ENVIRONMENT and IO-AREA-POOL. These are system and user storage areas used again and again in file accesses.
The maximum improvement in performance is achieved by making the system areas resident. In order to do this, the user must have the appropriate authorization in the user catalog (DMS-TUNING-RESOURCES=*EXCLUSIVE-USE) and make a suitable entry in the RESIDENT-PAGES operand in the user catalog and when starting the task.