MongoDB Advanced Cheat Sheet DATA | Aggregation + Perfo...

Quick Start with mongodb advanced

Production-ready compilation flags and build commands

Aggregation Pipeline: QUICK START (5s)

Copy → Paste → Live

db.orders.aggregate([{ $match: { status: 'A' } }, { $group: { _id: '$cust_id', total: { $sum: '$amount' } } }, { $sort: { total: -1 } }])

[ { _id: 'abc', total: 500 }, ... ]. Learn more in 'mongodb aggregation vs mapreduce' section

⚡ 5s Setup

When to Use mongodb advanced

Decision matrix per scegliere la tecnologia giusta

IDEAL USE CASES

Real-time analytics using the Aggregation Pipeline vs MapReduce
High-volume transaction processing with ACID compliance
Geo-distributed data with sharding and zone-aware replication

AVOID FOR

Strict relational data enforcement without validation schemas
Storing large binary blobs (use GridFS instead)
Complex multi-collection joins requiring high consistency (consider relational)

Core Concepts of mongodb advanced

Production-ready compilation flags and build commands

Aggregation Pipeline: Stage Flow

Pipelines process documents sequentially. See 'mongodb aggregation examples' below.

⚠️ Common Error

Putting $match after $group

✓ Solution

Always filter ($match) early to reduce dataset size

+300% Speed

Indexing strategies: ESR Rule

Equality, Sort, Range. The optimal order for compound index fields.

+10x Query Speed

mongodb lookup with pipeline: Advanced Joins

Performing uncorrelated sub-queries inside a lookup stage.

2x faster vs application-side joins

Sharding & Replication: Write Concern

w: 'majority' ensures durability across nodes.

⚠️ Common Error

Using w:1 for critical data

✓ Solution

Set w:majority in connection string

mongodb time series data: Collections

Native optimization for IoT/metric data in 5.0+.

-70% Storage

mongodb advanced Code Snippets

Copy-paste ready code blocks with real-world use cases

JAVASCRIPT

Advanced $lookup (Uncorrelated Subquery)

db.users.aggregate([{ $lookup: { from: 'orders', let: { userId: '$_id' }, pipeline: [{ $match: { $expr: { $and: [{ $eq: ['$userId', '$$userId'] }, { $gt: ['$amount', 100] }] } } }], as: 'expensive_orders' } }])

Output

{ _id: 1, expensive_orders: [...] }

JAVASCRIPT

$facet for Multi-Faceted Search

db.products.aggregate([{ $facet: { 'categorized': [{ $sortByCount: '$category' }], 'priced': [{ $bucket: { groupBy: '$price', boundaries: , default: 'Other' } }] } }])

Output

{ categorized: [...], priced: [...] }

JAVASCRIPT

Window Functions ($setWindowFields)

db.sales.aggregate([{ $setWindowFields: { partitionBy: '$state', sortBy: { orderDate: 1 }, output: { runningTotal: { $sum: '$amount', window: { documents: ['unbounded', 'current'] } } } } }])

Output

Adds runningTotal field

JAVASCRIPT

Create Partial Index

db.users.createIndex({ email: 1 }, { unique: true, partialFilterExpression: { email: { $exists: true } } })

Output

Index created

JAVASCRIPT

Schema Validation (JSON Schema)

db.createCollection('students', { validator: { $jsonSchema: { bsonType: 'object', required: ['gpa'], properties: { gpa: { bsonType: 'double', minimum: 0, description: 'must be double >= 0' } } } } })

Output

{ ok: 1 }

JAVASCRIPT

Multi-Document Transaction

const session = db.getMongo().startSession(); session.startTransaction(); try { session.getDatabase('db').coll.insertOne({}); session.commitTransaction(); } catch (e) { session.abortTransaction(); }

Output

Transaction committed

JAVASCRIPT

$merge (Materialized View)

db.sales.aggregate([{ $group: { _id: '$date', total: { $sum: '$amount' } } }, { $merge: { into: 'daily_sales', whenMatched: 'replace' } }])

Output

Writes to daily_sales

JAVASCRIPT

Explain Execution Stats

db.collection.find({ status: 'A' }).explain('executionStats')

Output

{ executionStats: { totalDocsExamined: ... } }

JAVASCRIPT

Recursive Search ($graphLookup)

db.employees.aggregate([{ $graphLookup: { from: 'employees', startWith: '$reportsTo', connectFromField: 'reportsTo', connectToField: 'name', as: 'reportingHierarchy' } }])

Output

Adds reportingHierarchy array

JAVASCRIPT

Create Time Series Collection

db.createCollection('weather', { timeseries: { timeField: 'timestamp', metaField: 'sensorId', granularity: 'seconds' } })

Output

{ ok: 1 }

JAVASCRIPT

Change Stream Watch

const changeStream = db.collection.watch([{ $match: { 'fullDocument.status': 'urgent' } }]); changeStream.on('change', printjson);

Output

Real-time events

JAVASCRIPT

Bulk Write (Ordered)

db.collection.bulkWrite([{ insertOne: { document: { a: 1 } } }, { updateOne: { filter: { a: 2 }, update: { $set: { a: 3 } } } }])

Output

{ matchedCount: 1, ... }

JAVASCRIPT

Array Update with Filters

db.students.updateOne({ _id: 1 }, { $set: { 'grades.$[elem].mean': 100 } }, { arrayFilters: [{ 'elem.grade': { $gte: 85 } }] })

Output

Updates specific array elements

JAVASCRIPT

$redact for Security

db.docs.aggregate([{ $redact: { $cond: { if: { $eq: ['$level', 'public'] }, then: '$$KEEP', else: '$$PRUNE' } } }])

Output

Filtered document structure

JAVASCRIPT

Covered Query Example

db.users.find({ name: 'Alice' }, { _id: 0, name: 1 }).hint({ name: 1 })

Output

Result from index only

JAVASCRIPT

Update via Aggregation Pipeline

db.employees.updateMany({}, [{ $set: { fullName: { $concat: ['$first', ' ', '$last'] } } }])

Output

Fields computed and updated

Mastering mongodb advanced Commands

Production-ready compilation flags and build commands

$match

Filtered docs

Full Syntax

{ $match: { status: 'A' } }

DefaultN/A

Alternative$expr

Caveat

⚠️ Place first in pipeline

$group

Grouped results

Full Syntax

{ $group: { _id: '$field', count: { $sum: 1 } } }

DefaultN/A

Alternative$bucket

Caveat

⚠️ Memory limit 100MB

$lookup

Joined docs

Full Syntax

{ $lookup: { from: 'b', localField: 'a', foreignField: 'b', as: 'join' } }

DefaultLeft Outer Join

Alternative$graphLookup

Caveat

⚠️ Can be slow on large sets

$project

Reshaped docs

Full Syntax

{ $project: { name: 1, total: { $multiply: ['$price', '$qty'] } } }

DefaultPass-through

Alternative$unset/$set

Caveat

⚠️ Drops fields not listed

$unwind

1 doc per element

Full Syntax

{ $unwind: { path: '$tags', preserveNullAndEmptyArrays: true } }

DefaultDrops empty

Alternative$filter

Caveat

⚠️ Explodes document count

$merge

Writes to coll

Full Syntax

{ $merge: { into: 'coll', whenMatched: 'merge' } }

DefaultInsert

Alternative$out

Caveat

⚠️ Must be last stage

$setWindowFields

Adds window field

Full Syntax

{ $setWindowFields: { output: { rank: { $rank: {} } } } }

DefaultN/A

AlternativeClient-side calc

Caveat

⚠️ Requires MongoDB 5.0+

$unionWith

Combined stream

Full Syntax

{ $unionWith: { coll: 'archive', pipeline: [...] } }

DefaultN/A

Alternative$lookup

Caveat

⚠️ Like SQL UNION ALL

$replaceRoot

Promotes subdoc

Full Syntax

{ $replaceRoot: { newRoot: '$nestedDoc' } }

DefaultN/A

Alternative$project

Caveat

⚠️ Loses parent fields

$bucket

Bucket stats

Full Syntax

{ $bucket: { groupBy: '$age', boundaries: } }

DefaultError on outlier

Alternative$bucketAuto

Caveat

⚠️ Must specify 'default'

Production Examples in mongodb advanced

Real-world applications with measured performance metrics

optimize mongodb slow query: E-commerce Dashboard

Latency < 200ms

Real-time sales dashboard using aggregation with $facet

Build Command

db.orders.aggregate([{ $match: { date: { $gte: ISODate('2025-01-01') } } }, { $facet: { 'totalSales': [{ $group: { _id: null, val: { $sum: '$amount' } } }], 'topProducts': [{ $group: { _id: '$prodId', sold: { $sum: 1 } } }, { $sort: { sold: -1 } }, { $limit: 5 }] } }])

✅ Multi-report JSON

mongodb transactions production example: Inventory

Integrity: 100%

ACID transaction transferring stock between warehouses

Build Command

session.withTransaction(() => { db.inventory.updateOne({ sku: 'A', wh: 1 }, { $inc: { qty: -10 } }, { session }); db.inventory.updateOne({ sku: 'A', wh: 2 }, { $inc: { qty: 10 } }, { session }); })

✅ Consistent state

mongodb time series data: IoT Logging

Storage: -60%

Storing sensor data with automatic expiration

Build Command

db.createCollection('logs', { expireAfterSeconds: 3600, timeseries: { timeField: 'ts', metaField: 'device' } })

✅ Auto-pruning

Graph Social Network

Depth: 2

Finding friends of friends using $graphLookup

Build Command

db.users.aggregate([{ $match: { name: 'Alice' } }, { $graphLookup: { from: 'users', startWith: '$friends', connectFromField: 'friends', connectToField: 'name', maxDepth: 2, as: 'network' } }])

Materialized View Refresh

Time: 500ms

Incremental update of analytics collection

Build Command

db.events.aggregate([{ $match: { processed: false } }, { $group: { _id: '$type', count: { $sum: 1 } } }, { $merge: { into: 'analytics', whenMatched: [{ $addFields: { count: { $add: ['$count', '$$new.count'] } } }] } }])

Geo-Fencing Query

Index: 2dsphere

Finding users within radius

Build Command

db.places.find({ loc: { $nearSphere: { $geometry: { type: 'Point', coordinates: [ -73.9, 40.7 ] }, $maxDistance: 1000 } } })

✅ Nearby points

Common Production Fixes for mongodb advanced

Production-tested solutions for common errors (2500+ cases resolved)

Executor error during find command :: caused by :: Sort operation used more than the maximum 33554432 bytes of RAM

40%

Context

Sorting without an index or on large dataset

Production Fix

Create an index matching the sort keys or use `{ allowDiskUse: true }` in aggregation (slower).

Verification✅ ✅ Query completes

Status

Production-tested solution

WriteConflict error: this operation conflicted with another operation

25%

Context

High contention on same document in transaction

Production Fix

Implement retry logic for the transaction block (MongoDB drivers usually provide a helper).

Verification✅ ✅ Transaction succeeds

Status

Production-tested solution

BSONObj size: 17000000 is invalid. Size must be between 0 and 16793600

20%

Context

Unbounded array growth or grouping massive buckets

Production Fix

Use `$unwind` before processing or change schema to reference model instead of embedding.

Verification✅ ✅ Insert succeeds

Status

Production-tested solution

Regular expression is invalid: PCRE limits exceeded

15%

Context

Inefficient regex query

Production Fix

Use `$text` index search or ensure regex is anchored `^prefix` to use index.

Verification✅ ✅ Query matches

Status

Production-tested solution

Replication lag is high

30%

Context

Secondary cannot keep up with primary write load

Production Fix

Enable flow control, upgrade hardware, or optimize Write Concern to throttle writes.

Verification✅ ✅ Lag < 1s

Status

Production-tested solution

mongodb advanced Common Pitfalls & Fixes

Using $where or JavaScript
Frequency: 30%
Cause: Legacy queries, prevents index use
Var
Avg fix time
Fix
Refactor to use Aggregation Operators ($expr)
✓ ✅ Scalable
Large Skip/Limit Pagination
Frequency: 60%
Cause: Cursor must iterate all skipped docs
Var
Avg fix time
Fix
Use Keyset Pagination (seek method) on indexed field
✓ ✅ O(1) Access
Indexing Low Cardinality Fields
Frequency: 40%
Cause: Boolean or Gender fields inefficient for index
N/A
Avg fix time
Fix
Use Compound Index with high cardinality fields first
✓ ✅ Efficiency
Monotonically Increasing Shard Key
Frequency: 20%
Cause: Using _id or timestamp in hash sharding
N/A
Avg fix time
Fix
Use Hashed Sharding on key `_id: 'hashed'`
✓ ✅ Distribution
Unbounded Document Growth
Frequency: 35%
Cause: Pushing to array indefinitely
N/A
Avg fix time
Fix
Use Bucketing pattern or `$slice` in updates
✓ ✅ Stability
No Authentication in Dev
Frequency: 50%
Cause: Binding to 0.0.0.0 default
5m
Avg fix time
Fix
Enable `security.authorization: enabled`
✓ ✅ Secure
Ignoring Write Errors
Frequency: 30%
Cause: Fire and forget code
N/A
Avg fix time
Fix
Always check `writeResult` or try/catch
✓ ✅ Reliability
Querying Arrays without ElemMatch
Frequency: 40%
Cause: Matches across different elements
N/A
Avg fix time
Fix
Use `$elemMatch` for precise object matching
✓ ✅ Accuracy
Fetching Unnecessary Fields
Frequency: 70%
Cause: Returning full docs (16MB)
N/A
Avg fix time
Fix
Use Projection `{ field: 1 }`
✓ ✅ Network IO
Running Aggregations on Primary
Frequency: 25%
Cause: Default read preference
N/A
Avg fix time
Fix
Use `readPreference: 'secondaryPreferred'` for analytics
✓ ✅ Availability

mongodb advanced Troubleshooting Guide

Common mongodb advanced errors with root cause analysis and verified fixes

Connection pool filled up

Symptom

Timeout waiting for connection

Root Cause

Application leaking connections

Fix

Increase `maxPoolSize` or fix app logic to close clients.

Verification

✓db.serverStatus().connections

Replication oplog window too short

Symptom

Secondary falls off oplog

Root Cause

High write volume vs oplog size

Fix

Increase oplog size (online in 4.4+ via `replSetResizeOplog`).

Verification

✓rs.printReplicationInfo()

Cursor not found

Symptom

Long query fails mid-stream

Root Cause

Session timeout (default 30m)

Fix

Refresh session or use `noCursorTimeout` (carefully).

Verification

✓Logs

Key too large to index

Symptom

Index build fail

Root Cause

Value > 1024 bytes

Fix

Hash the field or use `hashed` index.

Verification

✓Index exists

HostUnreachable

Symptom

Driver cannot connect

Root Cause

Network whitelist / Bind IP

Fix

Check `net.bindIp` in mongod.conf and AWS Security Groups.

Verification

✓telnet host 27017

Memory usage high (OOM)

Symptom

Mongod killed

Root Cause

Unconstrained sorting/aggregations

Fix

Set `wiredTigerCacheSizeGB` appropriately (usually 50% RAM).

Verification

✓free -m

Balancer not moving chunks

Symptom

Uneven shards

Root Cause

Balancer window or jumbo chunks

Fix

sh.startBalancer() or clear jumbo flag.

Verification

✓sh.status()

Document validation failure

Symptom

Write error

Root Cause

Schema validator mismatch

Fix

Check `db.getCollectionInfos()` validator rules.

Verification

✓Validate payload

Max BSON depth exceeded

Symptom

Nested document error

Root Cause

Nesting > 100 levels

Fix

Flatten schema design.

Verification

✓Schema check

Orphaned documents

Symptom

Count mismatch in sharding

Root Cause

Failed migrations

Fix

Run `cleanupOrphaned` command.

Verification

✓count()

Elite Pro Hacks For mongodb advanced

Advanced performance tips and optimizations for mongodb advanced

Performance tuning: Hinting Indexes

Code

db.coll.find({...}).hint({ indexName: 1 })

ImprovementForce plan selection

Caveat

⚠️ Maintenance burden

Compact Collection

Code

db.runCommand({ compact: 'myColl' })

ImprovementReclaims disk space

Caveat

⚠️ Blocks operations (pre-4.4)

Javascript in Aggregation

Code

{ $function: { body: function(name) { return name.toUpperCase() }, args: ['$name'], lang: 'js' } }

ImprovementComplex logic possible

Caveat

⚠️ Very slow (V8 engine)

Atlas Search Index Definition

Code

{ mappings: { dynamic: true } }

ImprovementLucene-powered search

Caveat

⚠️ Atlas only

Hidden Indexes

Code

db.coll.hideIndex('index_name')

ImprovementSafe index removal test

Caveat

⚠️ 4.4+

mongodb advanced Production Workflows

Complete CI/CD pipelines from prototype to production deployment for mongodb advanced

Slow Query Optimization

Step 1OpID 123

Identify

db.currentOp({ secs_running: { $gt: 1 } })

✅

Step 2COLLSCAN warning

Analyze

db.coll.find(...).explain('executionStats')

✅

Step 3Index Built

Index

db.coll.createIndex({ field: 1 })

✅

Step 4Low latency

Verify

explain() -> IXSCAN

✅

✓

✅ Performance Optimized

Schema Migration (Zero Downtime)

Step 1Data flowing

Dual Write

App writes to oldField AND newField

✅

Step 2Historical data updated

Backfill

db.coll.updateMany({ new: { $exists: false } }, [{ $set: { new: '$old' } }])

✅

Step 3Verified reads

Switch Read

App reads newField

✅

Step 4Schema clean

Cleanup

db.coll.updateMany({}, { $unset: { old: 1 } })

✅

✓

✅ Migrated

Sharding Setup

Step 1Enabled

Enable

sh.enableSharding('myDB')

✅

Step 2Index ready

Index

db.coll.createIndex({ shardKey: 'hashed' })

✅

Step 3Sharding started

Shard

sh.shardCollection('myDB.coll', { shardKey: 'hashed' })

✅

✓

✅ Distributed

Backup & Restore

Step 1dump.gz

Dump

mongodump --uri='...' --archive=dump.gz --gzip

✅

Step 2Restored

Restore

mongorestore --uri='...' --archive=dump.gz --gzip

✅

✓

✅ Data Safe

Rolling Index Build

Step 1Node secondary

Take Secondary out

rs.stepDown() (if primary)

✅

Step 2Built on secondary

Build Index

db.coll.createIndex()

✅

Step 3All nodes indexed

Repeat

Cycle through all nodes

✅

✓

✅ No Primary Lock

⚡ Aggregation Grouping (1M documents)

Performance Gain

+1400%

Baseline

Standard

Time

4500ms

Memory

150MB

Throughput

220 ops/sec

Optimized

Enhanced

Time

300ms

Memory

20MB

Throughput

3300 ops/sec

Overall Gain+1400%

🔬

Methodology

Added Covering Index on Group Field vs Collection Scan

On This Page

Quick Start with mongodb advanced

When to Use mongodb advanced

IDEAL USE CASES

AVOID FOR

Core Concepts of mongodb advanced

mongodb advanced Code Snippets

Mastering mongodb advanced Commands

$match

$group

$lookup

$project

$unwind

$merge

$setWindowFields

$unionWith

$replaceRoot

$bucket

Production Examples in mongodb advanced

optimize mongodb slow query: E-commerce Dashboard

mongodb transactions production example: Inventory

mongodb time series data: IoT Logging

Graph Social Network

Materialized View Refresh

Geo-Fencing Query

Common Production Fixes for mongodb advanced

Executor error during find command :: caused by :: Sort operation used more than the maximum 33554432 bytes of RAM

WriteConflict error: this operation conflicted with another operation

BSONObj size: 17000000 is invalid. Size must be between 0 and 16793600

Regular expression is invalid: PCRE limits exceeded

Replication lag is high

mongodb advanced Common Pitfalls & Fixes

Using $where or JavaScript

Large Skip/Limit Pagination

Indexing Low Cardinality Fields

Monotonically Increasing Shard Key

Unbounded Document Growth

No Authentication in Dev

Ignoring Write Errors

Querying Arrays without ElemMatch

Fetching Unnecessary Fields

Running Aggregations on Primary

mongodb advanced Troubleshooting Guide

Connection pool filled up

Replication oplog window too short

Cursor not found

Key too large to index

HostUnreachable

Memory usage high (OOM)

Balancer not moving chunks

Document validation failure

Max BSON depth exceeded

Orphaned documents

Elite Pro Hacks For mongodb advanced

Performance tuning: Hinting Indexes

Compact Collection

Javascript in Aggregation

Atlas Search Index Definition

Hidden Indexes

mongodb advanced Production Workflows

Slow Query Optimization

Identify

Analyze

Index

Verify

Schema Migration (Zero Downtime)

Dual Write

Backfill

Switch Read

Cleanup

Sharding Setup

Enable

Index

Shard

Backup & Restore

Dump

Restore

Rolling Index Build

Take Secondary out

Build Index