Database Optimizer

# Database Optimizer

Senior database optimizer with expertise in performance tuning, query optimization, and scalability across multiple database systems.

## When to Use This Skill

- Analyzing slow queries and execution plans
- Designing optimal index strategies
- Tuning database configuration parameters
- Optimizing schema design and partitioning
- Reducing lock contention and deadlocks
- Improving cache hit rates and memory usage

## Core Workflow

1. **Analyze Performance** — Capture baseline metrics and run `EXPLAIN ANALYZE` before any changes
2. **Identify Bottlenecks** — Find inefficient queries, missing indexes, config issues
3. **Design Solutions** — Create index strategies, query rewrites, schema improvements
4. **Implement Changes** — Apply optimizations incrementally with monitoring; validate each change before proceeding to the next
5. **Validate Results** — Re-run `EXPLAIN ANALYZE`, compare costs, measure wall-clock improvement, document changes

> ⚠️ Always test changes in non-production first. Revert immediately if write performance degrades or replication lag increases.

## Reference Guide

Load detailed guidance based on context:

| Topic | Reference | Load When |
|-------|-----------|-----------|
| Query Optimization | `references/query-optimization.md` | Analyzing slow queries, execution plans |
| Index Strategies | `references/index-strategies.md` | Designing indexes, covering indexes |
| PostgreSQL Tuning | `references/postgresql-tuning.md` | PostgreSQL-specific optimizations |
| MySQL Tuning | `references/mysql-tuning.md` | MySQL-specific optimizations |
| Monitoring & Analysis | `references/monitoring-analysis.md` | Performance metrics, diagnostics |

## Common Operations & Examples

### Identify Top Slow Queries (PostgreSQL)
```sql
-- Requires pg_stat_statements extension
SELECT query,
       calls,
       round(total_exec_time::numeric, 2)  AS total_ms,
       round(mean_exec_time::numeric, 2)   AS mean_ms,
       round(stddev_exec_time::numeric, 2) AS stddev_ms,
       rows
FROM   pg_stat_statements
ORDER  BY mean_exec_time DESC
LIMIT  20;
```