1. Index manquants

Problème :

// No index on 'email' field
db.users.find({ email: "user@example.com" })

Solution :

// Create index
db.users.createIndex({ email: 1 })

2. Requêtes regex inefficaces

Problème :

// Case-insensitive regex without index
db.users.find({ name: /john/i })

Solution :

// Use text index or exact match
db.users.createIndex({ name: "text" })
db.users.find({ $text: { $search: "john" } })

3. Grandes opérations skip()

Problème :

// Skipping thousands of documents
db.collection.find().skip(10000).limit(10)

Solution :

// Use range queries with indexed field
db.collection.find({ _id: { $gt: lastSeenId } }).limit(10)

4. Sélection de champs inutiles

Problème :

// Fetching entire documents
db.users.find({ status: "active" })

Solution :

// Use projection
db.users.find({ status: "active" }, { name: 1, email: 1 })

5. Pipelines d'agrégation inefficaces

Problème :

// $match after $lookup
db.orders.aggregate([
  { $lookup: { ... } },
  { $match: { status: "completed" } }
])

Solution :

// $match first to reduce documents
db.orders.aggregate([
  { $match: { status: "completed" } },
  { $lookup: { ... } }
])

1. Tableaux non bornés

Problème :

// Array grows indefinitely
{
  userId: 123,
  activities: [/* thousands of items */]
}

Solution :

// Use separate collection or bucketing
{
  userId: 123,
  month: "2024-01",
  activities: [/* limited items */]
}

2. Encastrement excessif

Problème :

// Deeply nested documents
{
  user: {
    profile: {
      settings: {
        preferences: {
          // many levels deep
        }
      }
    }
  }
}

Solution :

// Flatten or use references
{
  userId: 123,
  profileId: 456
}

3. Documents volumineux

Problème :

// Documents approaching 16MB limit
{
  data: "very large string...",
  attachments: [/* large binary data */]
}

Solution :

// Store large data separately (GridFS or object storage)
{
  dataRef: "s3://bucket/key",
  attachments: [{ ref: "gridfs://id" }]
}

1. Ne pas utiliser la mise en commun des connexions

Problème :

// Creating new connection per request
app.get('/api/users', async (req, res) => {
  const client = await MongoClient.connect(uri);
  // ...
  await client.close();
});

Solution :

// Reuse connection pool
const client = new MongoClient(uri, { maxPoolSize: 50 });
await client.connect();

app.get('/api/users', async (req, res) => {
  const db = client.db();
  // ...
});

2. Ne pas fermer les curseurs

Problème :

// Cursor left open
const cursor = db.collection.find();
// Never closed

Solution :

// Always close cursors
const cursor = db.collection.find();
try {
  await cursor.forEach(doc => { /* process */ });
} finally {
  await cursor.close();
}

3. Trop de connexions

Problème :

// One connection per user session
const connections = new Map();
users.forEach(user => {
  connections.set(user.id, new MongoClient(uri));
});

Solution :

// Share connection pool across application
const client = new MongoClient(uri);
// All users share the same pool

1. Trop d'index

Problème :

// Index on every field
db.collection.createIndex({ field1: 1 })
db.collection.createIndex({ field2: 1 })
db.collection.createIndex({ field3: 1 })
// ... 20+ indexes

Impact : Ralentit les écritures et augmente l'espace de stockage.

Solution : Ne conserver que les index nécessaires et utiliser des index composés.

2. Mauvais ordre d'indexation dans les index composés

Problème :

// Query: { status: "active", createdAt: { $gt: date } }
// Index: { createdAt: 1, status: 1 }  // Wrong order

Solution :

// Correct order: equality first, range second
db.collection.createIndex({ status: 1, createdAt: 1 })

3. Ne pas utiliser de requêtes couvertes

Problème :

// Index exists but query not covered
db.users.createIndex({ email: 1 })
db.users.find({ email: "user@example.com" }, { name: 1, email: 1 })
// Still fetches documents

Solution :

// Include all projected fields in index
db.users.createIndex({ email: 1, name: 1 })
db.users.find({ email: "user@example.com" }, { name: 1, email: 1, _id: 0 })

Alerte CPU

Condition: CPU > 80% for 10 consecutive minutes
Action: Send notification to ops team
Escalation: Page on-call if > 90% for 15 minutes

Alerte mémoire

Condition: Memory > 85% for 15 consecutive minutes
Action: Send notification to ops team
Escalation: Auto-scale if > 95% for 10 minutes

Alerte au retard de réplication

Condition: Lag > 10 seconds
Action: Send notification immediately
Escalation: Page on-call if > 60 seconds

Alerte sur l'espace disque

Condition: Disk > 80%
Action: Send notification to ops team
Escalation: Create incident if > 90%