Implementation on Platforms for IBM AS/400

AS/400 architecture uses a single level storage architecture (single storage principle) to implement the R/3 Extended Memory model. For this memory architecture, the main memory and the disk from the system are handled as an one address space.

Even if a large address space is assigned as an R/3 memory unit, the single level storage architecture and the dynamic memory allocation of the AS/400 operating system enable unused memory pages to be transferred, and to be available for use by other requests. Furthermore, you do not have to copy data to or from the context of the R/3 work process.

AS/400 memory pools are assigned subsystems. The resource needs of an R/3 instance are handled within a subsystem. The entire memory available for an instance is the allocated memory for the corresponding subsystem with the description R3_, where represents the number of the R/3 instance. R/3 jobs compete for resources with other jobs assigned to the same memory pool. The AS/400 subsystem description defines the size of the memory assigned to the instance.

Implementing R/3 Extended Memory on AS/400 has the following effects:

• Roll area Unlike other platforms, user contexts are not swapped in or out of work processes using copying. Instead the roll area is implemented in the same way as the R/3 Extended Memory. Under AS/400, a roll-in is reached by setting pointers for the user roll memory.

The implementation enables the roll area setting to be at a higher value (max. 16 MB) so that the roll extension area in the R/3 Extended Memory model is not required. The memory from the roll area is dynamically allocated up to 16 MB according to the requirements of the executed dialog steps. If you require additional memory, extended memory is allocated as planned in the R/3 memory model.

The roll area parameters ztta/roll_area and ztta/roll_first are already set to their optimal values and cannot be changed.

Since no data is copied during the swapping, the corresponding system profile parameters are not used. You must set these parameters (rdisp/ROLL_MAXFS and rdisp/ROLL_SHM) to 0 (null).

• R/3 Paging AS/400 does not differentiate between the paging cache (R/3 system profile parameter rdisp/PG_SHM) and the paging file (R/3 system profile parameter rdisp/PG_MAXFS). The entire paging file is buffered. For this reason, the settings for rdisp/PG_SHM and rdisp/PG_MAXFS are identical.
• Shared Memory Pools You do not have to define or manage any shared memory pools (defined with the parameters ipc/shm_psize in the system profile). This means, you do not have to allocate the logical shared memory segments to the new shared memory pools.

The parameter ipc/shm_psize is ignored on AS/400.