Parameter
em/initial_size_MB
Sap User Parameters List
Extended Memory. SAP work process has a part reserved in its virtual address space for extended memory. This can be set using the size of extended memory using the profile parameter em/initialsizeMB: Extended Memory Pool Size.
Short text
- Parameter em/initialsizeMB. Short text Extended Memory Size. Parameter description Note the operating system dependency for Microsoft Windows. The value specifies the initial size of the memory area that SAP MemoryManagement manages as extended memory. The memory requirements forinteractive users' programs are met from this area.
- The majority of the user context is stored in the extended memory. Page management of this memory as a stack is not taken from the operating system; rather it is performed directly from the R/3 System. This extended memory is implemented as an unnamed mapped file (on AIX and optionally on HP-UX as shared memory).
- Em/initialsizeMB - This parameter specifies how much SAP extended memory is available on the SAP system. Es/maxsegsizeMB - Specifies the maximum size of an extended memory segment in the SAP system. Es/maxsegments - Specifies the number of extended memory segments in the SAP system.
Extended Memory Size
Parameter Description
Sap Parameter Values
Note the operating system dependency for Microsoft Windows.
The value specifies the initial size of the memory area that SAP Memory Management manages as extended memory. The memory requirements for interactive users’ programs are met from this area. This memory type can be assigned very quickly to changing work processes by mapping and therefore allows very fast context switches.
Aim
Ideally, this pool should be large enough to contain the total of all user contexts, so that context switching for all users could be performed at optimal speed. You can restrict the maximum usage of an individual user with the parameter ztta/roll_extension. This prevents one user or a small number of users using all of the extended memory. If the extended memory is exhausted, additional memory requests are satisfied from the roll area and then from from the local address area of a work process (heap, malloc). The data in the roll area must be copied during the context switch, while the data in the local process area leads to exclusive reservation of the entire work process (PRIV mode).
Ideally, this pool should be large enough to contain the total of all user contexts, so that context switching for all users could be performed at optimal speed. You can restrict the maximum usage of an individual user with the parameter ztta/roll_extension. This prevents one user or a small number of users using all of the extended memory. If the extended memory is exhausted, additional memory requests are satisfied from the roll area and then from from the local address area of a work process (heap, malloc). The data in the roll area must be copied during the context switch, while the data in the local process area leads to exclusive reservation of the entire work process (PRIV mode).
Parameter Unit
1 MB
Default Value
Platform-dependent, approximately 4 GB for 64-bit
Default Value
(other)
(other)
500 – 4096, in extreme cases much higher
• Around 5 MB x number of active users on the application server
• Additional tuning in accordance with the values from transaction ST02 (for individual application servers) or RZ03 (for all application servers)
• From values > 500, you should expect operating system restrictions that cannot be extended, particularly in 32 bit systems.
• Additional tuning in accordance with the values from transaction ST02 (for individual application servers) or RZ03 (for all application servers)
• From values > 500, you should expect operating system restrictions that cannot be extended, particularly in 32 bit systems.
Default Value
(Microsoft Windows and Linux)
(Microsoft Windows and Linux)
Do not change the default = PHYS_MEMSIZE manually, since extended memory increases dynamically when necessary. No further calculation or adjustment is necessary.
Who is permitted to make changes?
The customer. No manual maintenance is necessary for Microsoft Windows or Linux.
Are other parameters affected or dependent?
The value must be smaller than or equal to ( em/blocksize_KB * 16) and an integer multiple of (em/blocksize_KB / 1024).
Operating System Restrictions
The swap space must be large enough and should have a safety net of several hundred megabytes at all times. Use transactions ST06 and RZ03 (CCMS alerts) for monitoring. You may have to extend existing limits in the operating system:
• Maximum size of shared memory, mapped file, mprotect
• Address space limits for each process or in total
• You can use the test program ‘memlimits’ to determine some of these limitations.
• Address space limits for each process or in total
• You can use the test program ‘memlimits’ to determine some of these limitations.
Microsoft Windows
A dynamic extension of the extended memory is implemented under Microsoft Windows and Linux. This means that if the current extended memory is insufficient, it is increased in steps of MAX (size [PHYS_MEMSIZE / 2], 2 GB). As a result of this mechanism, it is no longer necessary to maintain this profile parameter manually.
A dynamic extension of the extended memory is implemented under Microsoft Windows and Linux. This means that if the current extended memory is insufficient, it is increased in steps of MAX (size [PHYS_MEMSIZE / 2], 2 GB). As a result of this mechanism, it is no longer necessary to maintain this profile parameter manually.
Example
Application server with 1 GB main memory. PHYS_MEMSIZE is not maintained and its default value is the size of the main memory. Therefore, the initial size of the extended memory = 1 GB. If this size is not sufficient, the extended memory is increased in 500 MB steps until the maximum size em/max_size_MB (default for Microsoft Windows: 1.5 * PHYS_MEMSIZE), or until there is no further capacity in the address space and in the Microsoft Windows paging file.
Application server with 1 GB main memory. PHYS_MEMSIZE is not maintained and its default value is the size of the main memory. Therefore, the initial size of the extended memory = 1 GB. If this size is not sufficient, the extended memory is increased in 500 MB steps until the maximum size em/max_size_MB (default for Microsoft Windows: 1.5 * PHYS_MEMSIZE), or until there is no further capacity in the address space and in the Microsoft Windows paging file.
Application server with 8 GB of main memory, PHYS_MEMSIZE is not set. Initially, 5.6 GB of memory is allocated for extended memory. If this area is exhausted, the extended memory is extended in 2 GB steps until the free available memory in the operating system (free space in the paging file + free space in memory) is exhausted, or until em/max_size_MB is reached.
Central instance with 1 GB main memory. The database uses 400 MB and the SAP instance 600 MB of main memory. The value for PHYS_MEMSIZE is set to 600 in the instance profile. This means that the extended memory has an initial size of 600 MB, and if necessary extends itself in steps of 300 MB.
Database System Restrictions
Sap Extended Memory Parameter Definition
None
Database System Restrictions
None