Swap Space Requirements (SAP Library - SAP Memory Management (BC-CST-MM))

Swap Space Requirements

SAP application servers are important users of swap space. If the swap space on a computer 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.

The procedure depends on the operating system and is described in the relevant documentation:

Monitoring on UNIX

Monitoring on Windows NT

Monitoring on iSeries

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

The total size of the shared memory segments used by SAP, in particular the SAP buffer (for example, the program and table buffer).

Typical size: 200 to 700 MB

You can test this using the program sappfpar check pf=<profile>. (For more information on UNIX, see Determining Swap Space Requirements).

Number of work processes in an SAP 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 the parameter em/initial_size_MB, the SAP Extended Memory defines the SAP extended memory pool: This parameter allocates the swap space area that the SAP 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: 500 - 1500 MB

SAP limits defined for the heap memory (Private Memory) used by the work processes of an application server. The parameter abap/heap_area_total defines these limits (maximum private local (heap) memory that can be allocated to all SAP work processes). This is the upper limit of the swap memory that can be allocated to the SAP 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 depending 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 SAP System requires swap space. This allows you to 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

Note Rule of thumb:

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.

Set higher values for 64-bit system!

For more information on this, see Memory Management on 64-Bit Systems (UNIX).