event-store-design

# 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** |