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skills/optimizing-query-selection/references/performance-verification.md

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+# Performance Verification
+
+## Verification Checklist
+
+After optimization, verify improvements:
+
+1. **Data Size:** Check response payload size
+2. **Query Time:** Measure database query duration
+3. **Query Count:** Ensure single query instead of N+1
+4. **Memory Usage:** Monitor application memory
+
+## Enable Query Logging
+
+```typescript
+const prisma = new PrismaClient({
+  log: [
+    { emit: 'event', level: 'query' },
+  ],
+})
+
+prisma.$on('query', (e) => {
+  console.log('Query: ' + e.query)
+  console.log('Duration: ' + e.duration + 'ms')
+})
+```
+
+## Performance Testing
+
+```typescript
+async function testQueryPerformance() {
+  console.time('Unoptimized')
+  await prisma.user.findMany({
+    include: { posts: true }
+  })
+  console.timeEnd('Unoptimized')
+
+  console.time('Optimized')
+  await prisma.user.findMany({
+    select: {
+      id: true,
+      name: true,
+      _count: { select: { posts: true } }
+    }
+  })
+  console.timeEnd('Optimized')
+}
+```
+
+## Payload Size Comparison
+
+```typescript
+async function comparePayloadSize() {
+  const full = await prisma.post.findMany()
+  const optimized = await prisma.post.findMany({
+    select: {
+      id: true,
+      title: true,
+      excerpt: true,
+    }
+  })
+
+  console.log('Full payload:', JSON.stringify(full).length, 'bytes')
+  console.log('Optimized payload:', JSON.stringify(optimized).length, 'bytes')
+  console.log('Reduction:',
+    Math.round((1 - JSON.stringify(optimized).length / JSON.stringify(full).length) * 100),
+    '%'
+  )
+}
+```
+
+## Index Verification
+
+Check that indexes exist for queried fields:
+
+```sql
+-- PostgreSQL
+SELECT indexname, indexdef
+FROM pg_indexes
+WHERE tablename = 'Post';
+
+-- MySQL
+SHOW INDEXES FROM Post;
+```
+
+## Production Monitoring
+
+Monitor in production:
+
+1. **APM tools:** Track query performance over time
+2. **Database metrics:** Monitor slow query log
+3. **API response times:** Measure endpoint latency
+4. **Memory usage:** Track application memory consumption
+
+## Expected Improvements
+
+After optimization:
+
+- **Query count:** Reduced to 1-2 queries (from N+1)
+- **Response size:** 60-90% smaller payload
+- **Query time:** Similar or faster
+- **Memory usage:** 50-80% lower