Show HN: A strongly-typed document DB that runs on any transactional KV store

RefineDB

A strongly-typed document database that runs on any transactional key-value store.

Currently supported backends are:

• FoundationDB for distributed deployment.
• SQLite for single-machine deployment.
• A simple in-memory key-value store for the web playground.

Try RefineDB on the Web Playground!

Warning: Not ready for production.

Motivation

Databases should be more scalable than popular SQL databases, more structured than popular NoSQL databases, and support stronger static type checking than any of the current databases. So I decided to build RefineDB as "the kind of database that I want to use myself".

RefineDB will be used as the database service of rusty-workers.

Architecture

Getting started

Examples are a TODO but rdb-analyzer's tests and rdb-server (which uses RefineDB itself to store metadata) should give some basic insight on how the system works.

Schemas and the type system

In RefineDB, schemas are defined with types. For example, a part of a schema for a simple blog would look like:

type SiteConfig {
  site_name: string,
  registration_open: int64,
}

type BlogPost {
  @primary
  id: string,
  author_email: string,
  author_name: string,
  title: string,
  content: string,
  access_time: AccessTime,
}

type AccessTime {
  create_time: int64,
  update_time: int64,
}

export SiteConfig site_config;
export set<BlogPost> posts;

The primitive types are:

• int64: 64-bit signed integer.
• double: IEEE 754 double-precision floating point number.
• string: UTF-8 string.
• bytes: Byte array.
• set<T>: A set with element type T.

Sum types are nice to have too, but I haven't implemented it yet.

Queries: the TreeWalker VM and RefineAsm

Queries in RefineDB are encoded as data flow graphs, and query execution is graph reduction.

The TreeWalker VM is a massively concurrent data flow virtual machine for running the queries, but I haven't written documentation on its internals.

RefineAsm is the textual representation of the query graph, with some syntactic sugar to make writing it easier.

An example RefineAsm script for adding a post to the above blog schema:

type PostMap = map {
  id: string,
  author_email: string,
  author_name: string,
  title: string,
  content: string,
  access_time: map {
    create_time: int64,
    update_time: int64,
  },
};
export graph add_post(root: schema, post: PostMap) {
  s_insert root.posts $ call(build_post) [post];
}
graph build_post(post: PostMap): BlogPost {
  return build_table(BlogPost)
    $ m_insert(access_time) (build_table(AccessTime) post.access_time) post;
}

Storage plan and schema migration

A storage plan is how a schema maps to entries in the key-value store. By separating schemas and storage plans, RefineDB's schemas are just "views" of the underlying keyspace and schema changes are fast.

During a migration, added fields are automatically assigned new storage keys, and removed fields will not be auto-deleted from the storage. This allows multiple schema versions to co-exist, enables the client to choose which schema version to use, and prevents unintended data deletion.

Storage design doc

License

MIT

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