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.
This is described in more detail in the R/3 note 95454.
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. |
See also:
Shared Memory ID under IBM AIXThese recommendations depend not only on whether the alternative method of implementing extended memory is active, but also on the AIX version used.
The following R/3 notes relate to memory management under AIX:
Note Number |
Short text |
28992 |
AIX Number of shared memories exceeds 10 |
33576 |
Memory management in releases as of 3.0C, UNIX and NT |
36410 |
AIX Early versus late swap space allocation |
78498 |
High paging rate on AIX 4.x database servers |
95454 |
Large amount of extended memory on AIX |
124555 |
AIX Recommendation for maximum extended memory |
132748 |
AIX ES SHM_SEGS error handling corrected |
143646 |
AIX patches for new memory management (95454) |
115220 |
Signal 11 and signal 4 on AIX |