Spare core reserved
- Default value
- Parameter type
- Where set
- On User 0's parameter line
- Related products
- Model 204 V2.1 or earlier
SPCORE specifies the minimum amount of storage to leave unallocated at the end of Model 204 initialization.
After initialization, Model 204 uses for this spare core include:
- Small control blocks when files are opened
- Output buffers for directed output (USE) data sets, deferred update data sets, or CCASNAP
- Host Language Interface IFAM1 or IFAM4 application program storage
- Application Subsystem control blocks
- Dynamically allocated files and printer control blocks
SPCORE sets the minimum amount of reserved virtual storage. The actual amount of reserved storage available to you during the run is SPCORE bytes plus the number of region size bytes that are unallocated after Model 204 initialization has completed. This actual amount, which you can check with the VIEW command, is often considerably greater than the CCAIN SPCORE value you specified.
In z/OS, a number of bytes of virtual storage equal to your SPCORE setting is reserved above the line, and the same number is reserved below the line. The BTB amount is ignored in Model 204 7.7 and higher if the NUMBUFG parameter setting is greater than 0.
You can use the STORCUR, STORINIT, and STORMAX Model 204 parameters to help you determine your site's storage requirements. For more information about storage allocation, see Dynamic storage allocation tracking.
SPCORE for Application Subsystem control blocks
Control blocks are allocated from spare core for use by active subsystems. Use the following calculation to determine the number of bytes required for one subsystem, which can include Parallel Query Option/204 remote file subsystem members:
228 + NRMTFILE + NFILES + (40 * SCLASSes) + NRMTLOCS + (93 * filemembers) + ((36 + (7 + SCLASSes) / 8) * (procedures + 1)) + 40 bytes for each stopped file or group
- NRMTFILE and NRMTLOCS are Model 204 parameters.
- filemembers are the files that belong to the subsystem.
- SCLASSes is the number of subsystem user privilege classes.
- 40 bytes for each stopped file or group is the number of bytes returned to spare core if the subsystem is stopped or the file or group is started.
SPCORE for VSAM clusters
External access to VSAM clusters increases the requirements for dynamically allocated storage available at execution time. The amount of such storage is controlled by SPCORE in the z/OS version of Model 204. z/VSE users can refer to the discussion of the SPCORE parameter in VSAM I/O processing for further information.
SPCORE size requirements for VSAM clusters depend on the following factors:
- Where the VSAM access method modules are to be loaded. If they are not loaded in the public system area (LPA for z/OS, SVA for z/VSE), approximately 280K bytes are required to load the VSAM modules.
- The number of strings (STRNO) for each VSAM file and the
BUFFER SPACEparameter defined in the VSAM cluster definition. The product of these parameters determines the amount of storage required for each open VSAM file.
For information on external access to VSAM clusters, see External file identification.
SPCORE for FLOD exits
You must allocate additional working storage space to use the FLOD exit feature. Set the SPCORE parameter to allow 100 bytes per FLOD exit program.
Calculating increase to SPCORE for MQ/204 statistics
To calculate the additional bytes of SPCORE required to accommodate the MQ/204 statistics, use the following formula:
60 + (NUSERS * 120) = bytes of additional SPCORE required
The initial 60 bytes are required for the system statistics block (60 bytes for MQ/204 statistics). The 120 bytes for each user includes 60 bytes for the user statistics block and 60 bytes for the since-last statistics block for MQ/204 statistics.