Comment by wefarrell
3 years ago
"Your product asks will consistently want to combine these data sources (they don't know how your distributed databases look, and oftentimes they really do not care)."
This isn't a problem if state is properly divided along the proper business domain and the people who need to access the data have access to it. In fact many use cases require it - publicly traded companies can't let anyone in the organization access financial info and healthcare companies can't let anyone access patient data. And of course are performance concerns as well if anyone in the organization can arbitrarily execute queries on any of the organization's data.
I would say YAGNI applies to data segregation as well and separations shouldn't be introduced until they are necessary.
"combine these data sources" doesn't necessarily mean data analytics. Just as an example, it could be something like "show a badge if it's the user's birthday", which if you had a separate microservice for birthdays would be much harder than joining a new table.
Replace "people" with "features" and my comment still holds. As software, features, and organizations become more complex the core feature data becomes a smaller and smaller proportion of the overall state and that's when microservices and separate data stores become necessary.