Event Store Design
Comprehensive guide to designing event stores for event-sourced applications.
When to Use This Skill
- Designing event sourcing infrastructure
- Choosing between event store technologies
- Implementing custom event stores
- Optimizing event storage and retrieval
- Setting up event store schemas
- Planning for event store scaling
Core Concepts
1. Event Store Architecture
┌─────────────────────────────────────────────────────┐
│ Event Store │
├─────────────────────────────────────────────────────┤
│ ┌─────────────┐ ┌─────────────┐ ┌─────────────┐ │
│ │ Stream 1 │ │ Stream 2 │ │ Stream 3 │ │
│ │ (Aggregate) │ │ (Aggregate) │ │ (Aggregate) │ │
│ ├─────────────┤ ├─────────────┤ ├─────────────┤ │
│ │ Event 1 │ │ Event 1 │ │ Event 1 │ │
│ │ Event 2 │ │ Event 2 │ │ Event 2 │ │
│ │ Event 3 │ │ ... │ │ Event 3 │ │
│ │ ... │ │ │ │ Event 4 │ │
│ └─────────────┘ └─────────────┘ └─────────────┘ │
├─────────────────────────────────────────────────────┤
│ Global Position: 1 → 2 → 3 → 4 → 5 → 6 → ... │
└─────────────────────────────────────────────────────┘2. Event Store Requirements
| Requirement | Description |
|---|---|
| Append-only | Events are immutable, only appends |
| Ordered | Per-stream and global ordering |
| Versioned | Optimistic concurrency control |
| Subscriptions | Real-time event notifications |
| Idempotent | Handle duplicate writes safely |
Technology Comparison
| Technology | Best For | Limitations |
|---|---|---|
| EventStoreDB | Pure event sourcing | Single-purpose |
| PostgreSQL | Existing Postgres stack | Manual implementation |
| Kafka | High-throughput streaming | Not ideal for per-stream queries |
| DynamoDB | Serverless, AWS-native | Query limitations |
| Marten | .NET ecosystems | .NET specific |
Templates and detailed worked examples
Full template library and detailed worked examples live in references/details.md. Read that file when you need the concrete templates.
Best Practices
Do's
- Use stream IDs that include aggregate type -
Order-{uuid} - Include correlation/causation IDs - For tracing
- Version events from day one - Plan for schema evolution
- Implement idempotency - Use event IDs for deduplication
- Index appropriately - For your query patterns
Don'ts
- Don't update or delete events - They're immutable facts
- Don't store large payloads - Keep events small
- Don't skip optimistic concurrency - Prevents data corruption
- Don't ignore backpressure - Handle slow consumers
