Why OER and not EM

Hi,

I recently came across a project where OER has been preferred over EM considering the huge volume of data to be handled on a daily basis.

On trying to delve further, I discovered that Serial number generation will not be taken care by OER.
Serial numbers are already available from a different system. In such a scenario, can anyone help me with how OER is capable of handling
huge volumes of data?
Also do we have any additional performance improving notes for OER and not EM?

In short, my query is, what enables OER handle large volumes of data and not EM if serial number generation is not being taken care by any of them?

Appreciate your inputs!!

Regards,

Sam