If a UPAD exit is provided (RPLWAITX flag - bit 5 at RPL +X'29') for a deferred request, VSAM takes the UPAD exit for event completion. When the request can be restarted, VSAM takes the UPAD exit for a POST if in cross-memory or SRB mode. If not in cross-memory or SRB mode, VSAM issues a POST SVC. The user-provided UPAD exit must return control to the posted request in VSAM at the point just following where control was given to the UPAD WAIT exit. For more information about UPAD and WAITX, see z/OS DFSMS Using Data Sets.

VSAM RLS does not support UPAD exits.