Specifying DISP=OLD, NEW, or MOD restricts access to a PDSE by
a single job, started task, or TSO/E user. DISP=SHR lets multiple
jobs or users access the PDSE at the same time, and permits sharing
between DCBs in the same job step and in different jobs.
Member-Level Sharing. As in a PDS, multiple
copies (versions) of a member having the same name but different TTRs
can exist in a PDSE at the same time. Sharing is done on a "per
version" level. The sharing rules depend on whether the DCB is
open for input, update, or output.
INPUT—A version of a member can be
accessed by any number of DCBs open for input.
UPDATE—You cannot have any DCBs reading
a version of a member while another DCB is updating the same version
of the member.
OUTPUT—Any number of DCBs open for
output can create members at the same time. The members are created
in separate areas of the PDSE. If the members being created have the
same name (specified in the STOW done after the data is written),
the last version stowed is the version that is seen by users, and
the storage occupied by the first version is added to the available
space for the PDSE. You can have:
- Multiple DCBs reading and creating new versions of the same member
at the same time. Readers continue to see the "old" version until
they do a new BLDL or FIND by name.
- A single DCB updating a version of a member while multiple DCBs
are creating new versions of the member. The user updating the data
set continues to access the "old" version until the application
does a new BLDL or FIND by name.