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, as shown in the
following example, to enable the alternate CICS region to
start. In the example DD statement, the prefix of the data set reflects the release of CICS TS, and
the release level is assumed to be CICS TS6.2.
Sample job defining an auxiliary temporary storage data set
In Figure 1, the high level qualifier
(CICSTSnn.CICS) assumes the release level of CICS TS6.2. You must adapt it for your own
CICS release.
What to do next
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.