The service will need to read all its data and put it into objects, then extract the data from the objects to report it, then garbage collect all of that. For every single record in its entire data set.

You could say but oh, why not just return the underlying data without making objects? Well now you are exposing the underlying data format, which is what we’re trying to avoid by giving this job to the service.

And thus such patterns lead to the absurdity where 90% of enterprise apps do little actual computations beside serializing and deserializing JSON (or XML if a "legacy" app).

It's remarkable what you can do with just functions and nested data structures. Used to be big on the whole OOP thing, data roles, so much effort for so little.

Now I try to think about problems as "I have input data of shape X, I need shape Y" and fractally break it down into smaller shape-changes. I am kinda starting to get what those functional programmers are yammering on about.

The parent comment said “is asked for all records..GC hell “.

Since a micro service deals with only its own data and reporting is then across services, we’d need to query across services to get data and make sense of it. If we’d ever need to query all records, then such records would become domain objects in the micro services first before being passed along. A large number of domain objects would require a large amount of memory. Processing and releasing domain objects will result in GC on the released objects.