Configuration for AIX using Memory Management

Prerequisites

Particular functions of AIX (late swap allocation, disclaim) enable an alternative implementation of the Extended Memory with a size of several GB as of R/3 Release 3.1G kernel. A single user context can still only use approximately 1 GB of Extended Memory, but the sum of usable Extended Memory for all user contexts combined can be much higher.

Since a lot of Extended Memory is provided, you can set a high limit for the shared memory consumption. It is also no longer necessary to assign mainly heap memory in background processes to keep the usage of the Extended Memory low. Heap is particularly small on AIX.

You can also minimize roll memory, which accelerates the context switch (roll-in/out) and the dialog and background processing, for example, with synchronous updating.

Procedure

Recommended parameters in the instance profile:

Parameter	Recommendation	Meaning
ES/TABLE	SHM_SEGS	Switches to the alternative implementation of the Extended Memory (EM)
em/max_size_MB	4096	Enables maximum 4 GB of Extended Memory; can be larger if needed
ztta/roll_extension	500000000	Limit of approximately 500 MB (2 shared segments) of Extended Memory per user context
ztta/roll_area	3000000	Reduces consumption of roll memory in background processes
ztta/roll_first	1	Reduces consumption of roll memory in dialog processes
abap/heap_area_nondia	20000000 (20 MB)	Can be set relatively low, so that a heap bottle neck is avoided in the data segment

The following parameters should only be changed after consulting with SAP.

Parameter	Default	Meaning
es/shm_proc_seg_count	3	Specifies the number of shared memory segments that are used as shared and privately.
es/shm_max_priv_segs	2	This parameter must be lower by 1 than es/shm_proc_seg_count. (=>2*256 MB is usable)
es/shm_user_count	1024	This describes the maximum number of users in all open sessions.
es/shm_user_count		This specifies the maximum number of AIX system segments that ESSHM uses.