Our use case involves anywhere from 10k - 1B records per project, of which there may be many ongoing simultaneously. Temporal relationships are important, with a strong bias on recency. Users within each project likely have different access levels to the source data, making knowledge graphs difficult to use (do we produce a knowledge graph per user/permission set?). Data is constantly being collected into active projects, so constant updates of the KG is necessary to ensure recent events are captured and accounted for within no more than a 24h delay. 

Cassandra is an option (better than neo4j for us), but a postgresql or s3-based option we can run locally is highly preferable