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Event Sourcing Pattern

Description

Event Sourcing is a design pattern where state changes in a system are stored as a series of immutable events. The current state is derived by replaying these events in sequence, rather than storing the state directly.

How It Works

  1. Events are generated for each state change (e.g., “Order Placed”).
  2. Events are persisted to an event store.
  3. The system reconstructs state by replaying events from the store.

Advantages

  • Auditability: Provides a complete history of state changes.
  • Scalability: Efficiently handles high volumes of write operations.

Challenges

  • Complexity: Rebuilding state and handling event evolution can be tricky.
  • Storage: Large event histories may require significant storage.

Example Use Case

A banking application:

  • Events: “Account Created”, “Deposit Made”, “Withdrawal Made”.
  • State reconstruction: Replaying events rebuilds the account balance.