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em/initial_size_MB - Initial size of extended memory pool
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| Parameter : em/initial_size_MB |
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| Short description: Size of extended memory (Extended Memory) |
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| Description : |
| -------------- |
| Note the operating system dependency for Microsoft Windows. |
| |
| The value specifies the initial size of the memory area, which |
| is managed by SAP Memory Management as extended memory. |
| This satisfies the storage requests of the interactive |
| users' programs. This type of memory can be very quickly |
| assigned to changing work processes through |
| 'mapping'. This enables rapid context change. |
| |
| Aim: |
| Ideally this pool should be large enough to contain the total |
| of all user contexts, so that the context change of all |
| users can run as quickly as possible. |
| You can limit the maximum consumption of a user using |
| parameter %%ztta/roll_extension%%. This ensures that it is not |
| possible for one user or a few users to use up all of the |
| extended memory. |
| If the extended memory is exhausted, additional memory |
| requests are satisifed 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 context change, |
| while the data in the local memory of the work process leads to |
| exclusive assignment of the entire work process (PRIV mode). |
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| Unit : 1 MB |
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| Default : platform-dependent, approximately 4 GB for 64 bit |
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| Default value : (other) |
| 500 - 4096, in extreme cases much higher |
| - Around 5MB x number of active users on the application server |
| - Additional tuning in acc. with the values from transaction ST02 |
| (for individual app. servers) or RZ03 (for all app. servers) |
| - From values > 500, you should expect operating system |
| restrictions that cannot be extended, particularly |
| in 32 Bit systems. |
| |
| Suggested Value : (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. |
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| Who is permitted to make changes: The customer |
| No manual maintenance required for Microsoft |
| Windows and Linux |
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| Dependencies: |
| ---------------- |
| The value must be smaller than/equal to (%%em/blocksize_KB%% * 16)|
| and an exact multiple of (em/blocksize_KB / 1024). |
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| Operating system dependencies: |
| 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 |
| - And so on |
| You can use the test program "memlimits" to determine some of |
| these limits. |
| |
| 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 by the size [PHYS_MEMSIZE / 2]. |
| The default value is identical to PHYS_MEMSIZE. |
| PHYS_MEMSIZE. 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. This means that 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: 20 GB) is reached or until |
| there is no more address space in the NT page file. |
|
| 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. |
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| Database dependencies: None |
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| Short Description : Initial size of extended memory pool
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| Applications Area : ExtMemory
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| Parameter Type : I
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| Changes allowed : X
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| Valid for Operating System : *
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| Dynamic switchable :
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| Same on all Servers :
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| Minimum : 128
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| Maximum : 64000
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