Event Store Design

Name: event-store-design
Rating: 62
Author: ranbot-ai

Comprehensive guide to designing event stores for event-sourced applications.

Do not use this skill when

•The task is unrelated to event store design
•You need a different domain or tool outside this scope

Instructions

•Clarify goals, constraints, and required inputs.
•Apply relevant best practices and validate outcomes.
•Provide actionable steps and verification.
•If detailed examples are required, open resources/implementation-playbook.md.

Use this skill when

•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

code

┌─────────────────────────────────────────────────────┐
│                    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

Template 1: PostgreSQL Event Store Schema

sql

-- Events table
CREATE TABLE events (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    stream_id VARCHAR(255) NOT NULL,
    stream_type VARCHAR(255) NOT NULL,
    event_type VARCHAR(255) NOT NULL,
    event_data JSONB NOT NULL,
    metadata JSONB DEFAULT '{}',
    version BIGINT NOT NULL,
    global_position BIGSERIAL,
    created_at TIMESTAMPTZ DEFAULT NOW(),

    CONSTRAINT unique_stream_version UNIQUE (stream_id, version)
);

-- Index for stream queries
CREATE INDEX idx_events_stream_id ON events(stream_id, version);

-- Index for global subscription
CREATE INDEX idx_events_global_position ON events(global_position);

-- Index for event type queries
CREATE INDEX idx_events_event_type ON events(event_type);

-- Index for time-based queries
CREATE INDEX idx_events_created_at ON events(created_at);

-- Snapshots table
CREATE TABLE snapshots (
    stream_id VARCHAR(255) PRIMARY KEY,
    stream_type VARCHAR(255) NOT NULL,
    snapshot_data JSONB NOT NULL,
    version BIGINT NOT NULL,
    created_at TIMESTAMPTZ DEFAULT NOW()
);

-- Subscriptions checkpoint table
CREATE TABLE subscription_checkpoints (
    subscription_id VARCHAR(255) PRIMARY KEY,
    last_position BIGINT NOT NULL DEFAULT 0,
    updated_at TIMESTAMPTZ DEFAULT NOW()
);

Template 2: Python Event Store Implementation

python

from dataclasses import dataclass, field
from datetime import datetime
from typing import Any, Optional, List
from uuid import UUID, uuid4
import json
import asyncpg

@dataclass
class Event:
    stream_id: str
    event_type: str
    data: dict
    metadata: dict = field(default_factory=dict)
    event_id: UUID = field(default_factory=uuid4)
    version: Optional[int] = None
    global_position: Optional[int] = None
    created_at: datetime = field(default_factory=datetime.utcnow)


class EventStore:
    def __init__(self, pool: asyncpg.Pool):
        self.pool = pool

    async def append_events(
        self,
        stream_id: str,
        stream_type: str,
        events: List[Event],
        expected_version: Optional[int] = None
    ) -> List[Event]:
        """Append events to a stream with optimistic concurrency."""
        async with self.pool.acquire() as conn:
            async with c