The value specifies the amount of memory that one user context can allocate to the SAP extended memory. This value is valid for all types of work processes.
You can also control the quotas for dialog and non-dialog work processes separately. To do this use parameters ztta/roll_extension_dia and ztta/roll_extension_nondia. For example, you can give a larger proportion of extended memory to batch processes than to dialog work processes.
The EM quotas for work processes must not be more than the total amount of extended memory. The total size of the extended memory is specified in the em/initial_size_MB parameter.
Using the CCMS alert monitor (transaction RZ20), you can determine how much extended memory your servers use. The peak value displays the “high water mark” (maximum allocation) for extended memory.
The graphic below shows this relationship:
If the value is exceeded, heap memory is allocated. The work process is assigned only to this user context and is no longer available for other user contexts, since it is switched to the PRIV mode (in the Work Process Monitor, transaction SM50). See: Private Memory
If the value is set too high, caused by a large user context, an extended memory bottleneck can occur. If a large user context fills the SAP extended memory, it can switch other smaller work processes used for user contexts into PRIV mode before their SAP extended memory limit has been used up.
The default value is platform-specific and is determined dynamically. The default value is specified in transaction RZ11. This value should not normally be changed.
If you have problems with the default value, SAP recommends that you test your system with a high value (at least 500 MB). If the PRIV mode is switched on prematurely, you can decrease the size.
To minimize the number of dialog work processes in the PRIV mode, keep in mind the following tips:
· em/initial_size_MB: should be significantly larger than ztta/roll_extension.
· rdisp/ROLL_SHM, rdisp/ROLL_MAXFS: If you increase the value of ztta/roll_area, you must adjust these parameters.