You can either define a VSAM data set for auxiliary temporary
storage as a single extent data set on a single volume using the sample
job described here, or use the CICS-supplied job DFHDEFDS. DFHDEFDS
creates the DFHTEMP data set as one of the data sets for a CICS region.
About this task
You must not define any extra associations for a temporary
storage data set. For example, do not define a PATH. Doing so causes
CICS startup to fail. Do not allocate the DFHTEMP data set from an
SMS data class using extended addressability because CICS does not
support this.
Procedure
Consider adding multiple extents and multiple volumes for
the data set.
The sample job produces a single-extent data
set defined on a single volume, but you might experience channel and
arm contention if auxiliary temporary storage is used heavily.
To use DASD space more efficiently, you could define the DFHTEMP
data set with a primary extent large enough for normal activity, and
with secondary extents for exceptional circumstances, such as unexpected
peaks in activity.
Add a data definition statement for the DFHTEMP data set
to the startup job stream.
The temporary storage data set
is a passively shared data set, owned by the active CICS region, but
allocated to both the active and alternate CICS regions. Although
the alternate CICS region does not open this data set before takeover,
it is allocated at job step initiation, so you must specify DISP=SHR
on the DD statement to enable the alternate CICS region to start.
Use the TS system initialization parameter to specify an appropriate
number of VSAM buffers and strings for auxiliary temporary storage. CICS uses each VSAM buffer to
make a control interval from DFHTEMP available in CICS storage, and uses a VSAM string for each VSAM
I/O request between a buffer and DFHTEMP. Typically, the default setting of three buffers and three
strings is sufficient. For information about the performance considerations, see Auxiliary temporary storage: monitoring and tuning.