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skills/optimizing-query-performance/references/optimization-examples.md

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+# Optimization Examples
+
+## Example 1: Add Composite Index for Common Query
+
+**Scenario:** API endpoint filtering orders by userId and status, sorted by date
+
+**Current Schema:**
+
+```prisma
+model Order {
+  id        Int      @id @default(autoincrement())
+  userId    Int
+  status    String
+  createdAt DateTime @default(now())
+
+  user User @relation(fields: [userId], references: [id])
+}
+```
+
+**Query:**
+
+```typescript
+await prisma.order.findMany({
+  where: {
+    userId: req.user.id,
+    status: 'pending'
+  },
+  orderBy: { createdAt: 'desc' }
+})
+```
+
+**Optimization - Add Composite Index:**
+
+```prisma
+model Order {
+  id        Int      @id @default(autoincrement())
+  userId    Int
+  status    String
+  createdAt DateTime @default(now())
+
+  user User @relation(fields: [userId], references: [id])
+
+  @@index([userId, status, createdAt])
+}
+```
+
+Index covers filter AND sort, enabling index-only scan.
+
+## Example 2: Optimize Bulk Insert
+
+**Scenario:** Import 10,000 products from CSV
+
+**SLOW Approach:**
+
+```typescript
+for (const row of csvData) {
+  await prisma.product.create({
+    data: {
+      name: row.name,
+      sku: row.sku,
+      price: parseFloat(row.price)
+    }
+  })
+}
+```
+
+10,000 database round-trips = 60+ seconds
+
+**FAST Approach:**
+
+```typescript
+const products = csvData.map(row => ({
+  name: row.name,
+  sku: row.sku,
+  price: parseFloat(row.price)
+}))
+
+await prisma.product.createMany({
+  data: products,
+  skipDuplicates: true
+})
+```
+
+1 database round-trip = <1 second
+
+**Even Better - Chunked Batches:**
+
+```typescript
+const BATCH_SIZE = 1000
+
+for (let i = 0; i < products.length; i += BATCH_SIZE) {
+  const batch = products.slice(i, i + BATCH_SIZE)
+
+  await prisma.product.createMany({
+    data: batch,
+    skipDuplicates: true
+  })
+}
+```
+
+Progress tracking + failure isolation.
+
+## Example 3: Identify and Fix Slow Query
+
+**Enable Logging:**
+
+```typescript
+const prisma = new PrismaClient({
+  log: [{ emit: 'event', level: 'query' }]
+})
+
+prisma.$on('query', (e) => {
+  if (e.duration > 500) {
+    console.log(`SLOW QUERY (${e.duration}ms): ${e.query}`)
+  }
+})
+```
+
+**Detected Slow Query:**
+
+```
+SLOW QUERY (3421ms): SELECT * FROM "Post" WHERE "published" = true ORDER BY "views" DESC LIMIT 10
+```
+
+**Analyze with EXPLAIN:**
+
+```typescript
+await prisma.$queryRaw`
+  EXPLAIN ANALYZE
+  SELECT * FROM "Post"
+  WHERE "published" = true
+  ORDER BY "views" DESC
+  LIMIT 10
+`
+```
+
+**Output shows:** Seq Scan (full table scan)
+
+**Solution - Add Index:**
+
+```prisma
+model Post {
+  id        Int     @id @default(autoincrement())
+  published Boolean @default(false)
+  views     Int     @default(0)
+
+  @@index([published, views])
+}
+```
+
+**Verify Improvement:**
+
+After migration, same query executes in ~15ms (228x faster).