Change the database engine and serialization

[chiro-hiro]

SQLite is a wrong choice, the performance is poor and cost to serialize the JSON is very expensive. It would be better if we use rocksdb + profobuf. Just pure K-V and protobuf, we also able to implement gRPC base on the same protobuf.

[chirojr]

Triage: Enhancement

Request to change the database engine and serialization. Already labeled as enhancement and good first issue.

Classification: Enhancement