What are Identification Keys and custom Keys? where is the physical primay key is created where is it stored?

@asneelima

It's not limitation a in ACS rather in the context of Adobe Campaign Standard, 64-bit key refers to a 64-bit primary key (PKey) within the database schema. This means that the primary key field is designed to store larger integer values (64 bits) compared to the 32-bit keys used in some other Adobe Campaign versions like AC v7. Its a flexibility that ACS offers both 32/64 bit keys.

If you would like to understand the ACS datamodel, have a look at this documentation which has information about physical primary key.