I've been using Neo4j to store the bitcoin blockchain. Bitcoin transactions have a graph structure, and so by storing the entire blockchain in a graph database you can easily query for connections between different bitcoin addresses.
My experience with Neo4j has been a good one. The database is currently around 1TB and runs continuously without a problem. It's fast enough to use it as a public blockchain explorer, whilst simultaneously keeping up with importing all the latest transactions and blocks on the network.
It took some time to get the hang of the Cypher query language to get it to do what I want, but the browser it comes with is handy for learning via trial and error. I found the people on the Neo4j slack channel to be incredibly helpful with my questions.
You wouldn't be allowed to do this unfortunately.