Horizontal Scalability Problem for NoSQL Graph Banks

I am setting up a startup that is being incubated by the MBA of a school in Brazil, The project of our group is based on a social network in the linkedin format. I would like to know if memsql solved problems related to the horizontal scalability of nosql banks for example Neo4J. what if memsql is stable in relation to kafka?
Our initial expectation of launching the mobile application for IOS is a user base of 1 million people focused on customers in the United States.

Hey there - thanks for reaching out! MemSQL is a horizontally scalable, general purpose database that supports real-time ingestion from messaging sources like Kafka and others. We also serve as the mobile backend for many iOS applications. This sounds like an area that we’d be able to help in. Do you mind shooting me an email at stripathi@memsql.com so I can share some details and help you get up to speed?