em/initial_size_MB: Extended Memory Pool Size
This value specifies the extended memory pool size that the SAP System manages for the extended memory.
Unit: megabytes
Goal:
Ideally, this pool is large enough to contain the sum of all the user contexts. The pool must always be much larger than the size of the parameter
ztta/roll_extension. This parameter specifies how much extended memory can be allocated to a user context.If the pool is used up, heap memory is allocated (see
Private Memory and Allocating Memory for User Contexts). The work process switches to the PRIV mode and is reserved exclusively for the current user context. After processing the user context, the work process might restart automatically if the process size specified in abap/heaplimit is exceeded.
Rule of Thumb
Ensure that the pool is 10 to 15 times as larger as ztta/roll_extension. The exact value is oriented according to the available swap space and the number of users in the host system.
The swap space must be sized so that it can contain the SAP extended memory and has enough space for the SAP usage of heap memory (see
Swap Space Requirements). There must also be enough space available for competing system users outside of the SAP System. The swap space must also be large enough to ensure a safety reserve.