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S2 streams can serve as the shared log that keeps data in sync — between clients, between services, or between databases and downstream consumers.

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Event sourcing

Store events instead of current state. Append each change to a stream, and materialize state by replaying from the beginning — or from a known checkpoint. New consumers can be added at any time by reading the full history. S2’s strong consistency and durable total ordering of records make it a natural fit as a shared write-ahead log. See the kv-store blog post for a detailed example of how a replicated database with strong consistency can be built directly over the S2 primitive.

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WebSockets alternative

S2 streams can replace stateful WebSocket connections for bidirectional communication. Use two streams (one per direction) or a single shared stream. Records are durable and ordered, clients can reconnect and resume from their last sequence number, and there’s no connection state to manage server-side.

Y-S2

Yjs collaborative editing over S2

Sequin

Postgres CDC into S2

LiveStore

Sync engine powered by event sourcing