Swap Space Requirements for SAP Memory Management

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

Basic rules:

For optimal performance, the swap space should be approximately 3 times that of the main memory or be at least 3 GB, according to whichever value is higher.