Specifying the size of the hiperspace

When you create a hiperspace, you tell the system on the BLOCKS parameter how large to make that space, the largest size being 524,288 blocks. (The product of 524288 times 4K bytes is 2 gigabytes.) If your processor does not support an origin of zero, the limit is actually 4096 bytes less than 2 gigabytes.

Before you code BLOCKS, you should know two facts about the control an installation has on the size of data spaces and hiperspaces.

An installation can set limits on the amount of storage available for each address space for all data spaces and hiperspaces with a storage key of 8 through F. If your request for this kind of space would cause the installation limit to be exceeded, the system rejects the request with a nonzero return code and a reason code.
An installation sets a default size for data spaces and hiperspaces; you should know this size. If you do not use the BLOCKS parameter, the system creates a hiperspace with the default size. (The IBM® default size is 239 blocks.)

If you create the hiperspace with a storage key of 0 through 7, the system does not check the size against the total storage already used for data spaces and hiperspaces. If you create the hiperspace with a storage key of 8 through F, the system adds the initial size of the space to the cumulative total of all data spaces and hiperspaces for the address space and checks this total against the installation limit for an address space.

For information on the IBM defaults and how to change them, see Limiting hiperspace use.

The BLOCKS parameter allows you to specify a maximum size and initial size value.

The maximum size identifies the largest amount of storage you will need in the hiperspace.
An initial size identifies the amount of the storage you will immediately use.

As you need more space in the hiperspace, you can use the DSPSERV EXTEND macro to increase the size of the available storage, thus increasing the storage in the hiperspace that is available for the program. The amount of available storage is called the current size. (At the creation of a hiperspace, the initial size is the same as the current size.) When it calculates the cumulative total of data space and hiperspace storage, the system uses the current size of the hiperspace.

If you know the default size and want a hiperspace smaller than or equal to that size, use BLOCKS=maximum size or omit the BLOCKS parameter.

If you know what size hiperspace you need and are not concerned about exceeding the installation limit, set the maximum size and the initial size the same. BLOCKS=0, the default, establishes a hiperspace with the maximum size and the initial size both set to the default size.

If you do not know how large a hiperspace (with storage key 8 - F) you will eventually need or you are concerned with exceeding the installation limit, set the maximum size to the largest size you might possibly use and the initial size to a smaller amount, the amount you currently need.

Use the NUMBLKS parameter to request that the system return the size of the hiperspace it creates for you. You would use NUMBLKS, for example, if you did not specify BLOCKS and do not know the default size.

Figure 1 shows an example of using the BLOCKS parameter to request a hiperspace with a maximum size of 100,000 bytes of space and a current size of 20,000 bytes.

        DSPSERV CREATE,. . .,BLOCKS=(HSMAX,HSINIT)
        .
HSMAX   DC  A((1000000+4095)/4096)         HIPERSPACE MAXIMUM SIZE
HSINIT  DC  A((20000+4095)/4096)           HIPERSPACE INITIAL SIZE

Figure 1. Example of specifying the size of a hiperspace

This picture is described in preceding text.

Figure 1 shows how you can extend the available storage of the hiperspace in Figure 1.