Not totally sure about your question, but here some thoughts:
- You could connect your app to an postgres database and synchronize existing data into it. (https://community.mendix.com/link/space/databases/questions/100788)
– Did you use batch processing? This will help working with large datasets (https://medium.com/mendix/performance-modeling-in-mendix-batch-processing-1ed245a1e23b)