What are the limitations of CockroachDB when it horizontally scales?

[mubarakalmehairbi]

I would like to know what are the limitations of the horizontal scalability of CockroachDB. I ask this because the NoSQL databases I know have such limitations. For example, in MongoDB, new limitations arise when it horizontally scales:

• Before horizontally scaling, the database supports Unique constraints on the fields. However, when you horizontally scale it (by sharding), you cannot ensure uniqueness of fields.
• MongoDB does not recommend atomic transactions across the horizontally scaled collection (table)

so I was wondering if that was the case too for CockroachDB, are there limitations that I will face when CockroachDB scales?

• Will unique constraints still apply to a horizontally scaled table?
• Will the performance of atomic transaction in a horizontally scaled table degrades?