IOHEAP64 (AMODE 64 only)

IOHEAP64 controls the allocation of I/O heap storage for AMODE 64 applications and specifies how that storage is managed. Language Environment uses this storage when performing I/O for AMODE 64 applications.

The default value for AMODE 64 applications is IOHEAP64(1M,1M,FREE,12K,8K,FREE,4K,4K,FREE).

Syntax

                                                  .-KEEP-.                                .-KEEP-.   
>>-+-IOHEAP64-+--(--+--------+--,--+--------+--,--+------+--,--+--------+--,--+--------+--+------+-->
   '-IH64-----'     '-init64-'     '-incr64-'     '-FREE-'     '-init31-'     '-incr31-'  '-FREE-'   

                                 .-KEEP-.      
>--,--+--------+--,--+--------+--+------+--)-------------------><
      '-init24-'     '-incr24-'  '-FREE-'      

init64

Determines the initial allocation of I/O heap storage obtained above the 2G bar. Specify this value as nM bytes of storage. If a value of 0 or less is specified, the default is used.

incr64

Determines the minimum size of any subsequent increment to the I/O heap storage obtained above the 2G bar. Specify this value as nM bytes of storage. If a value less than 0 is specified, the default is used.

KEEP

Specifies that an increment to I/O heap storage is not released when the last of the storage within that increment is freed.

FREE

Specifies that an increment to I/O heap storage is released when the last of the storage within that increment is freed.

init31

Determines the minimum initial size of I/O heap storage that is obtained above the 16M line and below the 2G bar. This value can be specified as n, nK, or nM number of bytes. If 0 is specified, the initial storage is obtained on the first use and is based on the increment size. The amount of allocated storage is rounded up to the nearest multiple of 8 bytes.

incr31

Determines the minimum size of any subsequent increment to I/O heap storage that is obtained above the 16M line and below the 2G bar. This value can be specified as n, nK, or nM number of bytes. The amount of allocated storage is rounded up to the nearest multiple of 8 bytes.

init24

Determines the minimum initial size of I/O heap storage that is obtained below the 16M line. This value can be specified as n, nK, or nM number of bytes. If 0 is specified, the initial storage is obtained on the first use and is based on the increment size. The amount of allocated storage is rounded up to the nearest multiple of 8 bytes.

incr24

Determines the minimum size of any subsequent increment to I/O heap storage that is obtained below the 16M line. This value can be specified as n, nK, or nM number of bytes. The amount of allocated storage is rounded up to the nearest multiple of 8 bytes.

Performance consideration

You can improve performance with the IOHEAP64 runtime option by specifying values that minimize the number of times the operating system allocates storage. See RPTSTG for information about how to generate a report you can use to determine the optimum values for the IOHEAP64 runtime option.

For more information

• For more information about heap storage and heap storage tuning with storage report numbers, see z/OS Language Environment Programming Guide.
• For more information about the RPTSTG runtime option, see RPTSTG .