---
name: database-sharding
description: >
  Implement database sharding for horizontal scalability. Use when scaling large
  databases, distributing data across multiple servers, or designing sharded
  architectures.
---

# Database Sharding

## Table of Contents

- [Overview](#overview)
- [When to Use](#when-to-use)
- [Quick Start](#quick-start)
- [Reference Guides](#reference-guides)
- [Best Practices](#best-practices)

## Overview

Implement horizontal data partitioning across multiple database servers. Covers sharding strategies, consistent hashing, shard key selection, and cross-shard querying patterns.

## When to Use

- Database size exceeds single server capacity
- Read/write throughput needs horizontal scaling
- Geographic data distribution requirements
- Multi-tenant data isolation
- Cost optimization through distributed architecture
- Load balancing across database instances

## Quick Start

Minimal working example:

```sql
-- Define shard ranges
-- Shard 0: user_id 0-999999
-- Shard 1: user_id 1000000-1999999
-- Shard 2: user_id 2000000-2999999

CREATE TABLE users_shard_0 (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  user_id BIGINT NOT NULL,
  email VARCHAR(255) NOT NULL,
  created_at TIMESTAMP DEFAULT NOW(),
  CONSTRAINT shard_0_range CHECK (user_id BETWEEN 0 AND 999999)
);

CREATE TABLE users_shard_1 (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  user_id BIGINT NOT NULL,
  email VARCHAR(255) NOT NULL,
  created_at TIMESTAMP DEFAULT NOW(),
  CONSTRAINT shard_1_range CHECK (user_id BETWEEN 1000000 AND 1999999)
);

-- Function to determine shard
CREATE OR REPLACE FUNCTION get_shard_id(p_user_id BIGINT)
RETURNS INT AS $$
BEGIN
// ... (see reference guides for full implementation)
```

## Reference Guides

Detailed implementations in the `references/` directory:

| Guide | Contents |
|---|---|
| [Range-Based Sharding](references/range-based-sharding.md) | Range-Based Sharding |
| [Hash-Based Sharding](references/hash-based-sharding.md) | Hash-Based Sharding |
| [Directory-Based Sharding](references/directory-based-sharding.md) | Directory-Based Sharding |

## Best Practices

### ✅ DO

- Follow established patterns and conventions
- Write clean, maintainable code
- Add appropriate documentation
- Test thoroughly before deploying

### ❌ DON'T

- Skip testing or validation
- Ignore error handling
- Hard-code configuration values