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SpacetimeDB

SpacetimeDB is a fully-featured relational database system that integrates application logic directly within the database, eliminating the need for separate web or game servers. It supports multiple programming languages, including C# and Rust, allowing developers to write and deploy entire applications as a single binary. It is optimized for high-throughput and low latency multiplayer applications like multiplayer games.

Users upload their application logic to run inside SpacetimeDB as a WebAssembly module. There are three main features of SpacetimeDB: tables, reducers, and subscription queries. Tables are relational database tables like you would find in a database like Postgres. Reducers are atomic, transactional, RPC functions that are defined in the WebAssembly module which can be called by clients. Subscription queries are SQL queries which are made over a WebSocket connection which are initially evaluated by SpacetimeDB and then incrementally evaluated sending changes to the query result over the WebSocket.

All data in the tables are stored in memory, but are persisted to the disk via a Write-Ahead Log (WAL) called the Commitlog. All tables are persistent in SpacetimeDB.

SpacetimeDB allows users to code generate type-safe client libraries based on the tables, types, and reducers defined in their module. Subscription queries allows the client SDK to store a partial, live updating, replica of the servers state. This makes reading database state on the client extremely low-latency.

Authentication is implemented in SpacetimeDB using the OpenID Connect protocol. An OpenID Connect token with a valid iss/sub pair constitutes a unique and authenticable SpacetimeDB identity. SpacetimeDB uses the Identity type as an identifier for all such identities. Identity is computed from the iss/sub pair using the following algorithm:

1. Concatenate the issuer and subject with a pipe symbol (|).
2. Perform the first BLAKE3 hash on the concatenated string.
3. Get the first 26 bytes of the hash (let's call this idHash).
4. Create a 28-byte sequence by concatenating the bytes 0xc2, 0x00, and idHash.
5. Compute the BLAKE3 hash of the 28-byte sequence from step 4 (let's call this checksumHash).
6. Construct the final 32-byte Identity by concatenating: the two prefix bytes (0xc2, 0x00), the first 4 bytes of checksumHash, and the 26-byte idHash.
7. This final 32-byte value is typically represented as a hexadecimal string.

Byte Index: |  0  |  1  |  2  |  3  |  4  |  5  |  6  |  7  | ... | 31  |
            +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
Contents:   | 0xc2| 0x00| Checksum Hash (4 bytes) |  ID Hash (26 bytes) |
            +-----+-----+-------------------------+---------------------+
                      (First 4 bytes of           (First 26 bytes of
                       BLAKE3(0xc200 || idHash))    BLAKE3(iss|sub))

This allows SpacetimeDB to easily integrate with OIDC authentication providers like FirebaseAuth, Auth0, or SuperTokens.

Clockwork Labs, the developers of SpacetimeDB, offers three products:

1. SpacetimeDB Standalone: a source available (Business Source License), single node, self-hosted version
2. SpacetimeDB Maincloud: a hosted, managed-service, serverless cluster
3. SpacetimeDB Enterprise: a closed-source, clusterized version of SpacetimeDB which can be licensed for on-prem hosting or dedicated hosting