Hi, thanks for the feedback, I'm the creator of the framework. Answering your question: I chose LevelDB because it offers a good transactional capability for the key-value store, it also provides a very easy-to-use embedded library that is very stable while providing a decent performance and a binary serialization that helps me to store protobuf-serialized content. In summary, it's due to a mix of stability, database lock, binary store and transactional support. I use it to store item metadata (still work on to expose to the APIs) and model features/predictions.