MongoDB Indexing

Indexes dramatically speed up queries in MongoDB.

Types¶

• Single field
• Compound
• Multikey (arrays)
• Text
• Geospatial
• TTL (auto-delete)

Examples¶

db.orders.createIndex({userId:1,status:1,createdAt:-1})
db.sessions.createIndex({expiresAt:1},{expireAfterSeconds:0})

Explain¶

db.orders.find({userId:123}).explain('executionStats')
// COLLSCAN=bad, IXSCAN=good

• ESR: Equality, Sort, Range
• Partial indexes
• Covered queries
• Check unused ones

Indexes = Performance¶

Without indexes = collection scan. Always explain().