The correct choice is a non-relational database because it allows for the storage of unstructured or semi-structured data and provides the scalability required for the unpredictable access patterns of a social media application. Relational databases are less suitable for such workloads due to their rigid schema requirements, which limit flexibility in handling unstructured data. A data warehouse would not be the right choice for this scenario as it is optimized for complex queries and analytics on structured data, not the fast reads and writes of unstructured data typical of a social media app. Lastly, while file storage offers structured data storage capabilities and could handle unstructured data in files, it would not offer the same query flexibility or efficiency that a non-relational database would in handling diverse types of data interactions typical in a social media application.