distributed system – Building social graph for global users

We are building an app for social media similar to twitter with a follow functionality. When a person posts any new content, it should trigger feed updation for followers. I was wondering what is the data storage looks like for this scenario.

Does systems like twitter keep a global graph OR they have local replica in each region?
When a new post comes does it update a local posts table OR a global one?
How does feed generation work for global users?

Example scenario:
A person in US has followers in US and India.
Now when he makes a post, we need to update the feed of followers in US as well as India. Assuming the posts are stored in table, should that table be stored in one global region OR there should be 1 table per geography?