MongoDB Performance Optimization

Query Optimization Tips

# 1. Use projection to return only needed fields
# Bad
db.users.find({"status": "active"})

# Good
db.users.find(
    {"status": "active"},
    {"name": 1, "email": 1}  # Only fetch needed fields
)

# 2. Use limit() when you don't need all results
db.logs.find({"level": "error"}).sort("timestamp", -1).limit(100)

# 3. Use count_documents() with limit for existence check
exists = db.users.count_documents({"email": "test@test.com"}, limit=1) > 0

# 4. Avoid $where and $regex when possible
# Bad
db.users.find({"$where": "this.name.length > 10"})

# Good
db.users.find({"name": {"$exists": True}})  # Then filter in app

Index Best Practices

# 1. Create indexes for common queries
# Analyze your application's query patterns first

# 2. Use compound indexes effectively
# Order matters! (Equality, Sort, Range)
db.products.create_index([
    ("category", 1),     # Equality
    ("created_at", -1),  # Sort
    ("price", 1)         # Range
])

# 3. Don't over-index
# Each index:
# - Slows down writes
# - Uses memory
# - Needs maintenance

# 4. Remove unused indexes
for idx in db.users.list_indexes():
    print(f"{idx['name']}: {idx.get('key')}")

Bulk Operations

from pymongo import InsertOne, UpdateOne, DeleteOne

# Bulk writes are more efficient
operations = [
    InsertOne({"name": "Alice"}),
    InsertOne({"name": "Bob"}),
    UpdateOne({"name": "Charlie"}, {"$set": {"age": 30}}),
    DeleteOne({"name": "Dave"})
]

result = db.users.bulk_write(operations, ordered=False)
print(f"Inserted: {result.inserted_count}")
print(f"Modified: {result.modified_count}")

Connection Management

# 1. Reuse connections - don't create new client per request
# Bad (in web app)
def handle_request():
    client = MongoClient(...)  # New connection every request!
    ...

# Good (singleton pattern)
client = MongoClient(...)  # Create once

def handle_request():
    db = client.mydb  # Reuse connection
    ...

# 2. Configure connection pool
client = MongoClient(
    "mongodb://localhost:27017/",
    maxPoolSize=50,
    minPoolSize=10
)

Monitoring

# Server status
status = db.command("serverStatus")
print(f"Connections: {status['connections']['current']}")

# Collection stats
stats = db.command("collStats", "users")
print(f"Document count: {stats['count']}")
print(f"Size: {stats['size']} bytes")
print(f"Index size: {stats['totalIndexSize']} bytes")

# Current operations
ops = db.current_op()
for op in ops.get("inprog", []):
    if op.get("secs_running", 0) > 5:
        print(f"Slow op: {op}")

Performance Best Practices

Performance Best Practices

MongoDB Performance Optimization

Query Optimization Tips

Index Best Practices

Bulk Operations

Connection Management

Monitoring