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.agent/skills/database-design/optimization.md

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+# Query Optimization
+
+> N+1 problem, EXPLAIN ANALYZE, optimization priorities.
+
+## N+1 Problem
+
+```
+What is N+1?
+├── 1 query to get parent records
+├── N queries to get related records
+└── Very slow!
+
+Solutions:
+├── JOIN → Single query with all data
+├── Eager loading → ORM handles JOIN
+├── DataLoader → Batch and cache (GraphQL)
+└── Subquery → Fetch related in one query
+```
+
+## Query Analysis Mindset
+
+```
+Before optimizing:
+├── EXPLAIN ANALYZE the query
+├── Look for Seq Scan (full table scan)
+├── Check actual vs estimated rows
+└── Identify missing indexes
+```
+
+## Optimization Priorities
+
+1. **Add missing indexes** (most common issue)
+2. **Select only needed columns** (not SELECT *)
+3. **Use proper JOINs** (avoid subqueries when possible)
+4. **Limit early** (pagination at database level)
+5. **Cache** (when appropriate)