Event Sourcing as Append-Only State¶

Storing the sequence of state-changing events rather than current state enables complete audit trails, temporal queries, and state reconstruction while making the system's history explicit and immutable.

Tension Addressed¶

Write Optimization vs. Read Optimization

Recognizable As¶

Event logs, append-only storage, state derived from replaying events, temporal queries ("what was state at time T?"), event versioning

Canonical Sources¶

Fowler, "Event Sourcing" pattern (2005); Young, "CQRS Documents" (2010); Kleppmann, "Designing Data-Intensive Applications" (2017)

Transfers To¶

Version control systems, accounting ledgers, audit systems, debugging (reproducing historical state), undo/redo functionality

Trade-offs: - Events are immutable, requiring compensating events for corrections - Current state must be computed (though snapshots can cache it) - Event schema evolution requires careful versioning