Managing 64-bit addressing with cache manager

The IMS HP Change Accumulation Utility cache manager specifies the upper limit of storage above the bar that will be used by IMS HP Change Accumulation Utility for spill file data in memory.

IMS HP Change Accumulation Utility obtains cache manager control statements from the HPCCACHE DD statement. This optional cache is created by the IMS HP Change Accumulation Utility job during initialization and is dedicated to this job while IMS HP Change Accumulation Utility is running. The HPCCACHE DD statement must be provided in the JCL and the associated cache manager control statements must be correct. The cache is freed when the job terminates.

The following conditions govern the use of the IMS HP Change Accumulation Utility cache manager:

The cache manager is only available when the HPCCACHE DD is present in single address space mode.
IMS HP Change Accumulation Utility initialization checks for the HPCCACHE DD statement and will attempt to initialize the cache manager if the statement is present.
If successful, the IMS HP Change Accumulation Utility cache manager is in use and is dedicated to IMS HP Change Accumulation Utility.

If the HPCCACHE DD statement is not present, no cache will be used.
The cache manager use 64-bit addressing.
The maximum size of the 64-bit above the bar memory that the cache is allowed to use is defined by the SPACE control in the HPCCACHE DD statement.
IMS HP Change Accumulation Utility cache manager will not go beyond the limit set for above the bar memory allocations.
If the IMS HP Change Accumulation Utility cache manager is not initialized, then the IMS HP Change Accumulation Utility MEMLIMT command will control the memory above the bar.

Space above the bar is allocated by the IMS HP Change Accumulation Utility cache manager in 64MB increments as needed for the run. For example, when cache is used with a maximum setting of SPACE=2GB, and spill record processing needs only 1GB during this run, the total cache memory use above the bar will be 1GB for the run.

For example, the value set in the following HPCCACHE DD limits IMS HP Change Accumulation Utility use of above the bar memory to 4GB:

HPCCACHE DD * 
CACHE LEVEL=1,TYPE=64BIT,SPACE=4GB

HPCCACHE DD control statements

The IMS HP Change Accumulation Utility cache manager control statements are read from HPCCACHE DD, which must be a sequential data set or PDS member with DCB options RECFM FB or VB and LRECL <=255.

HPCCACHE DD control statements must adhere to the following conditions:

All keywords are required.
A "*" in first column makes the statement a comment.
CACHE LEVEL=level
level is a numeric value (1-n).

For this release of IMS HP Change Accumulation Utility, level is restricted to 1.

For example:
```
LEVEL=1 
```
CACHE TYPE=type
type is the name of a storage class.

For this release of IMS HP Change Accumulation Utility, type is restricted to 64BIT.

For example:
```
TYPE=64BIT 
```
CACHE SPACE=nMB|GB
The SPACE n is the maximum above the bar memory allocated for use by IMS HP Change Accumulation Utility.

For this release of IMS HP Change Accumulation Utility, n is restricted to nMB (megabytes) or nGB (gigabytes).

The cache manager cannot go beyond that limit in above the bar allocations.

For example, the following setting limits the cache manager to use up to 512MB of above the bar memory.
```
SPACE=512MB
```
The cache manager only uses memory when it needs it. IMS HP Change Accumulation Utility can use less memory than specified, but not more.

The memory size is rounded up to the 64MB boundary (the unit of allocation for the IMS HP Change Accumulation Utility cache manager).

Control statements must not be sequenced numbered.

For example, a control statement specified as:

HPCCACHE DD * 
CACHE LEVEL=1,TYPE=64BIT,SPACE=2GB                        00412020

receives the following error message:

BPE0003E AN ERROR OCCURRED PARSING CACHE CONTROL STATEMENT 
BPE0003E AT CHARACTER 73                                   
BPE0003E FAILING TEXT: "00412020        "                  
BPE0003E UNKNOWN POSITIONAL PARAMETER