database-optimizer Checked

Optimizes database queries and improves performance across PostgreSQL and MySQL systems. Use when investigating slow queries, analyzing execution plans, or optimizing database performance. Invoke for index design, query rewrites, configuration tuning, partitioning strategies, lock contention resolution.

Database Optimizer

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

Optimizes database queries and improves performance across PostgreSQL and MySQL systems. Use when investigating slow queries, analyzing execution plans, or optimizing database performance. Invoke for index design, query rewrites, configuration tuning, partitioning strategies, lock contention resolution.

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)

-- 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;

### Capture an Execution Plan

-- Use BUFFERS to expose cache hit vs. disk read ratio
EXPLAIN (ANALYZE, BUFFERS, FORMAT TEXT)
SELECT o.id, c.name
FROM   orders o
JOIN   customers c ON c.id = o.customer_id
WHERE  o.status = 'pending'
  AND  o.created_at > now() - interval '7 days';

### Reading EXPLAIN Output — Key Patterns to Find