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?

[vxtls]

MongoDB is a document database, while this is a relational database. The ACID characteristics of relational databases are generally better than those of document databases.

[yuzefovich]

Will unique constraints still apply to a horizontally scaled table?

Yes, uniqueness property will be enforced even if a table is split into multiple ranges (i.e. shards).

Will the performance of atomic transaction in a horizontally scaled table degrades?

If a transaction touches multiple ranges, regardless of whether those ranges are for the same table or not, the performance could be worse than if the transaction touched only a single range. However, this will be highly dependent on the nature of the transaction, so it's hard to provide any more specific answer.