Dear friends, Could you please let me know how to find the bytes use

Could you please elaborate on what do u mean by bytes in your question?

The primitive datatypes map directly to the corresponding primitive datatypes in Java. The CDTs map directly to plain Java Objects. There is no built in function which can tell you the size of a CDT or primitive data type in Appian. But, you can certainly develop a Java expression plugin for it.

@Chetan: Thank you for your quick response. As you said well about primitive and CDT, could you please let me aware of the both Complex System Data Types and Appian Object Data Types occupancy.

If you are busy let me have a link on this.

Not sure you have gone through this , the below link could help you in someway,
forum.appian.com/.../Custom_Data_Types_from_XSD.html

@Harsha: Thank you. It's making me to think more.