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You must ensure that Extended Memory is sufficiently large due to its intensive use. The prerequisite for this is a correspondingly large virtual memory area from Windows NT. As a basis, you need approximately 6 MB Extended Memory for each active user. Ensure that there is sufficient memory area by comparing the maximum Extended Memory used and memory created (Transaction ST02). Even during heavy system load, the value [ max use ] should not reach the value [ in memory ]. However, if this does occur, you must increase the profile parameter em/initial_size_MB accordingly.

You can use Transaction ST02 to check if the buffers from the roll and paging areas are the same size as the paging files. By comparing the values under Max. use, you can check if the buffer size is large enough.

You can determine from the row Extended Memory that the R/3 Extended Memory is sufficiently large. The value Max. use is, in this example, noticeably smaller than the created memory area (In memory). If both values are identical, you must increase the extended memory (profile parameter: em/initial_size_MB).

Keyword: BASIS
Title : SAP Memory Types :: Extended Memory

As previously described, the SAP Memory Manager copies the memory blocks of the roll area between the process address area and the shared memory with a memory copy command. However, the memory blocks of the Extended Memory are included again when the user context is changed. This is more efficient than copying blocks of the roll area. For this reason, the user context should largely be located in the Extended Memory. The profile parameter ztta/roll_first sets the size of the allocated memory in the roll area, before Extended Memory is used. If you set the profile parameter to 1, the SAP Memory Manager is told to use the Extended Memory immediately.

See: Parameter Overview for Windows NT

Definition

SAP R/3 Extended Memory is the core of the R/3 memory management system. Each R/3 work process has a part reserved in its virtual address space for Extended Memory (see Virtual Address Space in a Work Process). You can set the size using the profile parameter em/initial_size_MB. Under Windows NT, further memory is assigned dynamically as needed, and you can also set this amount.

Use

Structure

Windows NT: Implementation with Map/Unmap

UNIX: Implementation with Memory Protection (Protect/Unprotect)

Keyword: BASIS
Title : Checking Roll /Paging Area and Extended Memory with Tcode ST02

Use

Unit: 1 KB

Default value: 1024 (1 MB)

Recommended value: You may not change the default value.

Use

This value specifies the Extended Memory pool size that the R/3 System manages for the Extended Memory.

Goal:

Ideally, this pool is large enough to contain the sum of all the user contexts. The pool must always be larger than the size of the parameter ztta/roll_extension. This parameter specifies how much Extended Memory can be allocated to a user context.

If the pool is used up, heap memory is allocated (see Private Memory and Allocating Memory for User Contexts). The work process switches to the PRIV mode and is reserved exclusively for the current user context. After processing the user context, the work process may be restarted automatically, if the process size specified in abap/heaplimit was exceeded.

Basic rules: Ensure that the pool is 10 to 15 times as larger as ztta/roll_extension; The exact value is oriented according to the available swap space and the number of users in the host system.

Integration

The swap space must be sized so that it can contain the R/3 Extended Memory and has enough space for the R/3 usage of heap memory (see Swap Space Requirements). There must also be enough space available for competing system users outside of the R/3 System. The swap space must also be large enough to ensure a safety reserve.

Unit: 1 MB

Default value: 128 MB

Recommended value: 200 to 500 MB, approximately 5 MB for each R/3 user (pay attention to operating system dependencies)

You can find the values from the configuration examples (Contents button). You can find more information on Windows NT under Setting Dimensions for Sufficient Extended Memory.

Changes: Customers can make changes.

Use

The value specifies the amount of memory that one user context can allocate to the R/3 Extended Memory. Valid for all types of work processes.

The value refers to the R/3 Extended Memory that a user context allocates. If the value entered is exceeded, heap memory is allocated. The work process is assigned exclusively to this user context and is no longer available for other user contexts since it is switched to the PRIV mode (in the work process monitor, Transaction SM51). See: Private Memory

If the value is set too high, caused by a large user context, an Extended Memory bottleneck can occur. If a large user context fills the R/3 Extended Memory, other smaller user contexts could thereby switch work processes into PRIV mode before their R/3 Extended Memory limit has been used up.

SAP recommends that you test your system using the high default value (250 MB). If the PRIV mode is switched on prematurely, you can decrease the size to the recommended value.

Under IBM AIX and Siemens-Nixdorf SINIX, you can use parameter ztta/roll_extension to balance the effects of the relatively low values that you can set for abap/heap_area_nondia (see abap/heap_area_nondia: Heap Memory Limit for Non-Dialog Work Processes and Data Segment Sizes (UNIX)). On these platforms, the relatively small values for the maximum data segment size limit the heap memory available for background job processing.

In order for the background processing to have at least 500 MB memory allocated to it, SAP recommends setting the parameter ztta/roll_extension to the values listed below. Set these values only on the servers that are used primarily for background processing. Otherwise, the R/3 Extended Memory may be filled by just a few work processes and the PRIV mode will be switched on prematurely (see Recognizing and Correcting Problems).

• AIX values for background processing: > 300 MB
• SINIX values for background processing: > 200 MB

In order for the active processes to be executed, you must increase the value for em/initial_size_MB: Extended Memory Size. You can determine the amount of Extended Memory your servers allocates by using Transaction RZ03 (see Overview of All Application Servers). The peak value displays the "high water mark" (maximum allocation) for Extended Memory.

Under AS/400, you can increase the value as needed to enable the processes to use more Extended Memory.

Goal:

Minimize the number of dialog work processes in the PRIV mode.

Integration

• em/initial_size_MB: should be significantly larger than ztta/roll_extension.
• ztta/roll_area: a higher value saves on R/3 Extended Memory.
• rdisp/ROLL_SHM, rdisp/ROLL_MAXFS: If you increase the value of ztta/roll_area, you must adjust these parameters

Unit: Bytes

Default value: 250000000 (250 MB)

20971520 (20 MB) under AS/400

Recommended value: 500000000 (500 MB)

Changes: Customers can make changes. You can find the values from the configuration examples (Contents button).