I've personally been involved in a very large deployment of D365 Online which had many millions of rows of data in multiple entities. I architected and worked with consultants to design and build this solution.
We had the following:
- Over 18 million contacts
- Related to contacts, this resulted in 54 million records in the address table, and the same number in a hidden email address table
- The total database size was over 100GB
In general performance was fine. We did some work on the indexes on the contact table to ensure searches performed well. There was some learnings I took from this, but in general, Microsoft Support can provide advice on the best indexes to setup. These indexes are then used in Quick Find views and other searches in the application.
Do remember, CDS is the same database that D365 uses, when we built this application it was based on a SQL DB hosted and managed on a VM in the Azure DB. It has recently been migrated to V9 and I've been told performance is just as good now that it is on this version. CDS/D365 v9 is hosted in Azure SQL DB's.
I would never have an issue putting this size application on D365/CDS.
