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Keyword: BASIS
Title : SAP Version Management

An overview of the memory management parameters will be shown in the following sections.

A description of the parameter always follows the unit in which it is specified, the default value and a proposed value. The default value usually is based on a minimal value, therefore for very small R/3 installations (see Application Servers with Up to 15 Users), the proposed value is based on a midsize to large installation (see Application Servers with Up to 50 Users and Application Servers with Over 50 Users).

The specified default values and proposed values are based on UNIX systems; under Windows NT, the parameter setting is explained in the unit Parameter Overview for Windows NT.

abap/heaplimit: Work Process Startup

ztta/roll_extension: Extended Memory Limit

abap/heap_area_dia: Heap Memory Limit for Dialog Work Processes

abap/heap_area_nondia: Heap Memory Limit for Non-Dialog Work Processes

abap/heap_area_total: Heap Memory Limit

em/initial_size_MB: Extended Memory Pool Size

rdisp/ROLL_SHM: Roll Buffer Size

rdisp/ROLL_MAXFS: Maximum Roll File Size

rdisp/PG_SHM: Paging Buffer Size

rdisp/PG_MAXFS: Maximum Size of the R/3 Paging File

ztta/roll_area: Roll Area

ztta/roll_first: Initial Allocation Size from the Roll Area

em/blocksize_KB: Segment Size for the Extended Memory

em/stat_log_size_MB: Statistics - User Context Size

em/stat_log_timeout: Statistics - User Context Size

If with Transaction ST06 or on the CCMS Alert Monitor you notice a high paging rate in a memory pool, enlarge this pool.

• Machine Pool: This is always system pool 1.

The paging rate should be less than 10 faults per second.

• Other pools: The paging rate should be ideally less than 200 faults per second.

In the operating system OSF/1 from Digital Equipment Corporation, you must increase the value of the parameter VPAGEMAX for the Extended Memory by up to 800 MB (parameter em/initial_size_MB = 800) to 131072. You can find more information on larger memory amounts in the OSS Note 32915 in the OSS system.

VPAGEMAX defines the size of the unnamed mapped file for the R/3 Extended Memory.

The program sappfpar lets you check the minimum and maximum (worst case) swap space requirements for an R/3 application server. It also checks the shared memory requirements and if the parameters em/initial_size_MB and abap/heap_area_total are correctly set. Proceed as follows:

1. To check the instance profile for the R/3 application server, start the program sappfpar from the UNIX command line.

/usr/sap//SYS/exe/run/sappfpar check pf=/usr/sap//SYS/profile/ nr= name= | more

2. The program generates a list. Note the total value for the shared memory in the field Shared memory under Memory requirements estimated. This value corresponds to the size of the shared memory required for this profile, and must be calculated into the shared memory requirements for the new Memory Management.
3. At the end of the list, the program specifies the minimum swap space requirements, the maximum heap memory requirements and the swap space requirements in a worst case scenario:

Total, minimum requirement.....: 169.5 MB (shared memory requirement)
Process local heaps, worst case: 762.9 MB
(is set with abap/heap_area_total )
Total, worst case requirements: 962.5 MB

R/3 application servers are important users of swap space. If the swap space in a host system is used up, serious system problems occur as a result. Therefore, you must monitor swap space usage.

To monitor swap space, you can use either the monitoring tool for host operating systems or the system monitor from the SAP Computing Center Management System (CCMS). The CCMS Alert Monitor, which is available via the system monitor, issues warning messages if the swap space usage exceeds a preset limit. You can also display the present usage.

Also see:

Determining the Swap Space Currently Available

Determining the Swap Space Requirements

An R/3 application server divides its swap space with non-R/3 processes in the host system. The maximum swap space size that an R/3 application server can occupy is determined by the following factors:

• Total size of the extended memory buffer (for example, the program and table buffer)

Typical size: 200 to 500 MB

You can test this using the program sappfpar check pf= .

• Number of work processes in an R/3 server

Each work process requires approximately 12 MB of swap space plus the roll area of the active user context; therefore approximately 20 MB per work process.

• As with parameter
em/initial_size_MB, SAP Extended Memory defines (R/3 Extended Memory pool): This parameter assigns the swap space area that the R/3 System uses for its Extended Memory. The pool has a set size. The total size is allocated directly after starting the application server.

Typical values: approximately 500 MB

• R/3 limits for the local process memory (
Private Memory) for the work processes of an application server Parameter abap/heap_area_total defines these limits (maximum local private (heap) memory that can be assigned to all R/3 work processes) This is the upper limit of the swap memory that can be allocated to the R/3 work processes when they run in PRIV mode and use heap memory. The memory is allocated to the work processes in the application server taking this limit into account. The size used varies based on whether the work processes switch to or are restarted in the PRIV mode, when they leave the PRIV mode.

This parameter lets you foresee when the R/3 System requires swap space. This lets you prevent a critical shortage of swap space. Work processes cannot use heap memory resources anymore than specified in this parameter.

Typical values: 2 - 4 GB

The following prerequisites must be met so that you can use memory management with your R/3 System (Release > 4.0A):

• The swap space may not fall below a specified level.
• You may have to install additional main memory.
• You must reset various operating system parameters and, if necessary, they must be inserted in a new operating system kernel.
• You may also have to reconfigure hardware and software.

In the following sections, you will find information about the prerequisites for swap space and main memory.

For UNIX and Windows NT, refer to the following documents for more information about changes to the kernel parameters and software prerequisites:

• UNIX Systems: R/3 Installation on UNIX -- OS Dependencies. You receive this document with the installation and upgrade packages.
• Windows NT Systems: Documentation on installing and upgrading and in
Memory Management under Windows NT

The following documents contain details about hardware prerequisites for UNIX and Windows NT:

• For installations, you can find details in the installation documentation.
• For upgrades, you can find details in this document and the upgrade documentation. For additional information, see the upgrade and installation notes for the SAP online system as well.

Swap Space Requirements

Main Memory

Data Segment Size (UNIX)

Minimizing the Windows NT File Cache

VPAGEMAX under OSF/1

Shared Memory ID under IBM AIX

Memory Pool Requirements for AS/400

Checking the Hardware and Operating System of the Host System

Using the following parameters, you can limit the maximum use of the process-specific memory. This in turn limits the maximum use of temporary memory by an R/3 application server.

Consider the following parameters:

For more information about the function parameters, see Allocating Memory for User Contexts.

Temporary memory almost completely covers the memory requirements of R/3. The main consumers are:

• Internal buffers with a fixed share (PXA, table buffer, paging buffer)
• R/3 memory management (roll memory, Extended Memory, private memory) with a variable share depending on the number of users logged on and the application type (direct memory requirements)

Implementing the memory management system on AS/400 is described in Implementation on Platforms for IBM AS/400.

In the following tables, you will find information about the necessary settings for the memory management system.

• Check if your host system fulfills the SAP recommendations for main memory and swap space.

Check the resources and system-specific requirements on all host systems on which an R/3 server is to be installed. For more information, see Checking the Hardware and Operating System of the Host System.

• Set the R/3 profile parameter that uses the memory management system.

Set these parameters in the instance profile used by each R/3 application servers in your system. For more information, see the CCMS Guide.

If you modify the profiles directly with a system editor, you must perform an error check. For more information, see Checking the Hardware and Operating System of the Host System.

The values listed in the following table for the host systems and servers should ensure the best possible operation of your R/3 application sever.

Main Memory and Swap Space on the Host System

R/3 Profile Parameters

Prerequisites

Procedure

The memory management system is automatically activated and configured using your entries during the installation or the upgrade.

Prerequisites

Before you install the R/3 System or upgrade to a 4.x version, ensure that the host system(s) on which the R/3 application server is/are set up, fulfill all the requirements particularly regarding main memory and swap space.

For more information, see:

Operating System and Hardware Prerequisites.

Also refer to the installation checklist and the installation documentation OS Dependencies.

Configuring the Memory Management System

Checking and Adjusting the Configuration

Check the preconfigured memory management system and your host system using the following sample configuration and guidelines.

Requirements for the Host:

Checking the Hardware and Operating System of the Host System

Sample Configurations:

Application Server with Up to 15 Users

Application Server with Up to 50 Users

Application Server with Over 50 Users

Configuration Help for Various Platforms:

Configuration for UNIX / Windows NT

AS/400 Configuration

Memory Management under Windows NT

Configuration for AIX

Checking the Operation of the Memory Management System and Setting Necessary Parameters if Necessary

For more information, see:

Monitoring the Memory Management System

Important OSS Notes

The basis for the Zero Administration Memory Management under Windows NT is the dynamic Extended Memory. This technique provides you with a nearly unlimited memory resource. Initially, the extended memory is set to the size of the profile parameter phys_memsize ([PM]). If the user requires more memory, Extended Memory extends itself in steps from "[PM] / 2" up to the set limits in the profile parameter em/max_size_MB , or until the address space in the NT page file is used up. By setting the default value for em/max_size_MB to 2000 MB, the size of the NT page file represents the actual limit for extending the Extended Memory. The profile parameter phys_memsize determines how much of the total main memory is used by R/3. The parameter is entered according to the input at installation. The default value for phys_memsize is the size of the main memory [MM].

The memory allocation strategy for a non-dialog work process was changed as of Release 4.0B. Through the previous allocation sequence, the extended memory was protected to the benefit of the heap memory. This is no longer necessary when using the dynamic Extended Memory, and the allocation sequence of the batch work processes is identical to the sequence of the dialog work processes (see Allocating Memory for User Contexts). Another beneficial side effect is that you can avoid the PRIV mode (see Private Memory) for background work processes and thereby the expensive restarting of work processes.

Sequence of allocating memory for non-dialog work processes:

1. Roll memory until the limit
ztta/roll_first
2. Extended memory until the limit
min {em/address_space_MB, ztta/roll_extension}
3. Roll memory until the limit
ztta/roll_area
4. Heap memory until the limit
abap/heap_area_nondia

The basis for zero administration memory management is a sufficiently large NT page file. The previous recommendation

NT page file = 3 to 4 times the main memory size

still remains.

All relevant memory management parameters are set with an optimal default value so that all manual configurations are unnecessary.

See also: Memory Management under Windows NT

An application runs in an R/3 work process where an ABAP program is normally executed. The process requires memory to do this, which is allocated to it by the memory management system. The order in which the work process is assigned the memory type depends on the work process type, either dialog or non-dialog (see R/3 Memory Types), and the underlying operating system.

This is described in the section Allocating Memory for User Contexts.

The location of the various memory areas in the virtual address space is explained in Virtual Address Space of a Work Process.

The area of a user context that is directly accessible is now extended as needed, if the user context has expanded. For dialog work processes, the data of the user context, including internal tables, is located in this expandable area called Extended Memory. You can therefore access all the data in the user context. The data types Extract and Export to Memory remain in the SAP Paging.

The R/3 roll area is used for the initial memory assigned to a user context, and (if available) for additional memory if the Extended Memory is full.

The advantages of the SAP memory management require increased swap space and main memory. See: Operating System and Hardware Prerequisites.

The following diagram displays the memory types that can be assigned to R/3 work processes on the R/3 and operating system level. Here are the most important system profile parameters that control the availability of the memory types.

Whenever a dialog step is executed, a roll action occurs between the roll buffer in the shared memory and the memory area, which is allocated according to ztta/roll_first in a dialog process. Then the area in the shared memory is accessed that belongs to this user context.

The following illustration displays the roll process performed by the dispatcher.

• Roll-in: User-dependent data is rolled in from the common resource in the work process (and is processed there).
• Roll-out: User-dependent data is rolled out from the work process in the common resource (after the dialog step has ended).

The common resource stands for the different R/3 memory types:

This documentation introduces the SAP R/3 Memory Management System and explains which parameters are available and how you can set them to optimize your system.

This explains which hardware and operating system requirements you must fulfill and how you can monitor your memory management, discover and correct problems.

The documentation is made up of the following chapters:

You must monitor the operating system (swap space usage and operating system paging) and the status of the R/3 System. There are R/3 tools available for both of these purposes.

Monitoring the Status of the Operating System

All R/3 jobs are preset and run in the *BASE pool (system pool 2). Make as much memory as possible available for this pool. 150-200 MB is the absolute minimum. If you still have other applications running on your AS/400 system, assign them to the R/3 System with a separate pool.

Minimum memory for pool 2: 150 to 200 MB

Memory Pools on AS/400

Checking Page Fault Rates

The data segment size restricts the size of a user context that is executed as an R/3 background job. The default value is 64 MB, which is however, not sufficient and should be increased.

Set the data segment size for a process to the following values:

You can check data segment sizes using the R/3 test program memlimits. (You must stop the R/3 server to do this.) Note the output row that appears as follows: Process xxxxx allocating. The segment size is displayed in the row Size = .

For more detailed information, also refer to the R/3 installation guide in the section covering UNIX kernel parameters.

Procedure

/usr/sap//SYS/exe/run/memlimits | more

Result

The available swap space is given at the end of the program output in the output line Total available swap space: . The program also specifies, if the amount of swap space is adequate and determines the size of the file segments in the system.

All relevant memory management parameters are set with an optimal default value so that all manual configurations are unnecessary.

The following table gives you an overview of these values.

The Windows NT file cache directly competes with R/3 programs for working memory. It pushes other programs out of the memory. Therefore, you should minimize the file cache with the following configuration.

There is only one way to minimize the file cache under Windows NT. To do this, call the network setting (icon: Network) in the Control Panel.