Hello HyunKyu,
I am afraid that performance is more complex than just the domain model, it also has to do with the functionality you want to have in your application, which decides mainly how you need to store and retrieve your data.
Nonetheless, the domain model is the heart of your application here are some links to the best practices and you can decide which things suits your situation the best:
https://docs.mendix.com/refguide/community-best-practices-for-app-performance/
https://docs.mendix.com/howto/data-models/denormalize-data-to-improve-performance/
Hope this helps!
Kind Regards
Jelle