LIBHEAP64 (AMODE 64 only)

Derivation: LIBRARY HEAP storage for AMODE 64

The LIBHEAP64 runtime option controls the allocation of heap storage used by Language Environment for AMODE 64 applications and specifies how that storage is managed.

AMODE 64 default: LIBHEAP64=((1M,1M,FREE,16K,8K,FREE,8K,4K,FREE),OVR)


Syntax

                                             .-KEEP-.      
>>-LIBHEAP64--=--(--(--init64--,--incr64--,--+-FREE-+--,-------->

                         .-KEEP-.                            
>--init31--,--incr31--,--+-FREE-+--,--init24--,--incr24--,------>

   .-FREE-.        .-OVR----.      
>--+-KEEP-+--)--,--+-NONOVR-+--)-------------------------------><

init64: Determines the initial allocation of library 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 library 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 library heap storage is not released when the last of the storage within that increment is freed.
FREE: Specifies that an increment to library heap storage is released when the last of the storage within that increment is freed.
init31: Determines the minimum initial size of library heap storage that is obtained above the 16MB line and below the 2GB bar. This value can be specified as n, nK, or nM number of bytes. If a value of 0 or less is specified, the default is used. 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 library heap storage that is obtained above the 16MB line and below the 2GB bar. This value can be specified as n, nK, or nM number of bytes. If a value less than 0 is specified, the default is used. The amount of allocated storage is rounded up to the nearest multiple of 8 bytes.
init24: Determines the minimum initial size of library heap storage that is obtained below the 16MB line. This value can be specified as n, nK, or nM number of bytes. If a value of 0 or less is specified, the default is used. 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 library heap storage that is obtained below the 16MB line. This value can be specified as n, nK, or nM number of bytes. If a value less than 0 is specified, the default is used. The amount of allocated storage is rounded up to the nearest multiple of 8 bytes.
OVR: Specifies that the option can be overridden.
NONOVR: Specifies that the option cannot be overridden.

Performance considerations

To improve performance, use the storage report numbers generated by the RPTSTG runtime option as an aid in setting the initial and increment sizes for LIBHEAP64.

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 64-bit Virtual Addressing Mode.