Graph databases in Cosmos DB benefit from the same features, like the SQL API, it is globally distributed, scales independently throughput and storage, provides guaranteed latency, automatic indexing and more. So when relational databases choke with certain queries, No-SQL databases come to play.
Gremlin is the query language used by Apache Tinkerpop and it is implemented in Azure Cosmos DB. This language enables us to transverse graphs and answer complex queries that would be otherwise very expensive to run in traditional relational database engines.
Read on for a detailed example.