Bitsy is a embeddable in-memory graph database that is compatible with Tinkerpop3. It is based on these design principles: "No seek" (avoid disk seeks to maximize write throughput), "No socket" (embed within the application to reduce network/OS delays) and "No SQL" (leverage graph traversals for faster queries).
The write algorithms are designed to recover from crashes and consolidate work across threads for better performance in OLTP settings. The database can be backed up while it is operational using a JMX interface.
Bitsy can be queried using Gremlin and other Tinkerpop-compatible query languages, like SQL2Gremlin and Pixy.
Bitsy maintains a copy of the entire database in-memory. It also maintains a checkpoint of the database on disk.