ReddRadar
Agent skill
mongodb-indexing-optimization
Master MongoDB indexing and query optimization. Learn index types, explain plans, performance tuning, and query analysis. Use when optimizing slow queries, analyzing performance, or designing indexes.
Install this agent skill to your Project
npx add-skill https://github.com/pluginagentmarketplace/custom-plugin-mongodb/tree/main/skills/mongodb-indexing
SKILL.md
MongoDB Indexing & Optimization
Master performance optimization through proper indexing.
Quick Start
Create Indexes
// Single field index
await collection.createIndex({ email: 1 });
// Compound index
await collection.createIndex({ status: 1, createdAt: -1 });
// Unique index
await collection.createIndex({ email: 1 }, { unique: true });
// Sparse index (skip null values)
await collection.createIndex({ phone: 1 }, { sparse: true });
// Text index (full-text search)
await collection.createIndex({ title: 'text', description: 'text' });
// TTL index (auto-delete documents)
await collection.createIndex({ createdAt: 1 }, { expireAfterSeconds: 3600 });
List and Analyze Indexes
// List all indexes
const indexes = await collection.indexes();
console.log(indexes);
// Drop an index
await collection.dropIndex('email_1');
// Drop all non-_id indexes
await collection.dropIndexes();
Explain Query Plan
// Analyze query execution
const explain = await collection.find({ email: 'test@example.com' }).explain('executionStats');
console.log(explain.executionStats);
// Shows: executionStages, nReturned, totalDocsExamined, executionTimeMillis
Index Types
Single Field Index
// Index on one field
db.collection.createIndex({ age: 1 })
// Query uses index if searching on age
db.collection.find({ age: { $gte: 18 } })
Compound Index
// Index on multiple fields - order matters!
db.collection.createIndex({ status: 1, createdAt: -1 })
// Queries that benefit:
// 1. { status: 'active', createdAt: { $gt: date } }
// 2. { status: 'active' }
// But NOT: { createdAt: { $gt: date } } alone
Array Index (Multikey)
// Automatically created for arrays
db.collection.createIndex({ tags: 1 })
// Matches documents where tags contains value
db.collection.find({ tags: 'mongodb' })
Text Index
// Full-text search
db.collection.createIndex({ title: 'text', body: 'text' })
// Query
db.collection.find({ $text: { $search: 'mongodb database' } })
Geospatial Index
// 2D spherical for lat/long
db.collection.createIndex({ location: '2dsphere' })
// Find nearby
db.collection.find({
location: {
$near: { type: 'Point', coordinates: [-73.97, 40.77] },
$maxDistance: 5000
}
})
Index Design: ESR Rule
Equality, Sort, Range
// Query: find active users, sort by created date, limit age
db.users.find({
status: 'active',
age: { $gte: 18 }
}).sort({ createdAt: -1 })
// Optimal index:
db.users.createIndex({
status: 1, // Equality
createdAt: -1, // Sort
age: 1 // Range
})
Performance Analysis
Check if Query Uses Index
const explain = await collection.find({ email: 'test@example.com' }).explain('executionStats');
// IXSCAN = Good (index scan)
// COLLSCAN = Bad (collection scan)
console.log(explain.executionStats.executionStages.stage);
Covering Query
// Query results entirely from index
db.users.createIndex({ email: 1, name: 1, _id: 1 })
// This query is "covered" - no need to fetch documents
db.users.find({ email: 'test@example.com' }, { email: 1, name: 1, _id: 0 })
Python Examples
from pymongo import ASCENDING, DESCENDING
# Create index
collection.create_index([('email', ASCENDING)], unique=True)
# Compound index
collection.create_index([('status', ASCENDING), ('createdAt', DESCENDING)])
# Explain plan
explain = collection.find({'email': 'test@example.com'}).explain()
print(explain['executionStats'])
# Drop index
collection.drop_index('email_1')
Best Practices
✅ Index fields used in $match (early in pipeline) ✅ Use ESR rule for compound indexes ✅ Monitor index size and memory ✅ Remove unused indexes ✅ Use explain() to verify index usage ✅ Index strings with high cardinality ✅ Avoid indexing fields with many nulls ✅ Consider index intersection ✅ Regular index maintenance ✅ Monitor query performance
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