nderground uses DynamoDB and Amazon S3 to store almost all of the data in the nderground social network.
I was excited to read about Titan, which had an option to use DynamoDB as a backend. Unfortunately, it appears that JanusGraph is not continuing to support DynamoDB.
Perhaps this is motivated by the fact that DynamoDB is not open source (it’s an Amazon service).
However, DynamoDB is both extremely fast and cheap. There’s no license fee for DynamoDB, you only pay for the resources you use. DynamoDB is also an Amazon managed service, which means that until you get to massive scale you don’t need to do anything to increase capacity other than adjust the transaction allocation. There’s no need to shard the database or add additional servers.