---
name: database-performance-debugging
description: >
  Debug database performance issues through query analysis, index optimization,
  and execution plan review. Identify and fix slow queries.
---

# Database Performance Debugging

## Table of Contents

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

## Overview

Database performance issues directly impact application responsiveness. Debugging focuses on identifying slow queries and optimizing execution plans.

## When to Use

- Slow application response times
- High database CPU
- Slow queries identified
- Performance regression
- Under load stress

## Quick Start

Minimal working example:

```sql
-- Enable slow query log (MySQL)
SET GLOBAL slow_query_log = 'ON';
SET GLOBAL long_query_time = 0.5;

-- View slow queries
SHOW GLOBAL STATUS LIKE 'Slow_queries';
SELECT * FROM mysql.slow_log;

-- PostgreSQL slow queries
CREATE EXTENSION pg_stat_statements;
SELECT mean_exec_time, calls, query
FROM pg_stat_statements
ORDER BY mean_exec_time DESC LIMIT 10;

-- SQL Server slow queries
SELECT TOP 10
  execution_count,
  total_elapsed_time,
  statement_text
FROM sys.dm_exec_query_stats
ORDER BY total_elapsed_time DESC;

-- Query profiling
EXPLAIN ANALYZE
SELECT * FROM orders WHERE user_id = 123;
// ... (see reference guides for full implementation)
```

## Reference Guides

Detailed implementations in the `references/` directory:

| Guide | Contents |
|---|---|
| [Identify Slow Queries](references/identify-slow-queries.md) | Identify Slow Queries |
| [Common Issues & Solutions](references/common-issues-solutions.md) | Common Issues & Solutions |
| [Execution Plan Analysis](references/execution-plan-analysis.md) | Execution Plan Analysis |
| [Debugging Process](references/debugging-process.md) | Debugging Process |

## 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