MongoDB Mastery: all 66 lessons

Free MongoDB lessons from your first query to sharded clusters: CRUD, aggregation, indexes and explain(), schema design, transactions, replication, sharding, WiredTiger internals and operations. Every lesson has runnable examples in the interactive course.

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Level 1: Beginner

Documents, BSON, mongosh and your first CRUD queries.

What MongoDB is and when to use it · MongoDB Fundamentals · 15 min
MongoDB stores data as documents: JSON-like records with nested objects and arrays. This lesson explains the model, how it differs from relational databases, and where it fits.
Documents, collections and namespaces · MongoDB Fundamentals · 15 min
The rules every document follows: _id, field names, size limits, nesting, and how collections and databases are created.
mongosh, connection strings and tools · mongosh & Tools · 18 min
The shell is a full JavaScript environment. Learn how to connect, navigate, read cursors, script, and which companion tools exist.
mongosh configuration, scripting and legacy features to replace · mongosh & Tools · 20 min
Make mongosh yours with config and .mongoshrc.js, run scripts safely from the command line with EJSON output, and replace the features that old code and old tutorials still use:…
BSON types, ObjectId and type ordering · BSON Data Types · 18 min
Types decide how values compare, sort and index. Learn the important BSON types, how ObjectId works, and how MongoDB orders mixed types.
insertOne, insertMany and bulk writes · Inserting Documents · 15 min
Create documents safely: generated ids, ordered versus unordered batches, duplicate key errors and the write result.
Querying: equality, comparison and logic · Querying Documents · 20 min
find() with filters: equality, implicit AND, comparison operators, $in, $or, and querying nested fields with dot notation.
Missing fields, null, $type, $regex and $expr · Querying Documents · 18 min
The subtle operators: how null matches missing fields, existence checks, pattern matching, and comparing two fields of the same document.
Projection, sorting and pagination · Projection, Sort & Pagination · 20 min
Return only what you need, sort deterministically, and paginate without the skip trap.
Cursors: batches, getMore, timeouts and tailable cursors · Projection, Sort & Pagination · 24 min
A query does not return all its results at once. The server keeps a cursor and sends documents in batches. Learn how batches and getMore work, why cursors time out in the middle…
Update operators, upserts and replacements · Updating & Deleting · 22 min
Modify documents atomically with update operators, create-or-update with upserts, and read the result counters correctly.
Deleting data safely · Updating & Deleting · 12 min
deleteOne, deleteMany, drop, TTL expiry and soft deletes, plus a checklist for destructive operations in production.

Level 2: Intermediate

Arrays, aggregation, indexes, explain() and schema design.

Querying arrays and embedded documents · Arrays & Embedded Documents · 20 min
How a condition on an array field matches any element, why that surprises people, and how $elemMatch, $all and $size give you precise control.
Updating arrays: $push, $pull, positional operators · Arrays & Embedded Documents · 20 min
Add, remove and modify array elements in place, including the positional $, $[] and filtered $[id] operators.
The aggregation pipeline: $match, $group, $project, $sort · Aggregation Pipeline · 25 min
Pipelines transform documents stage by stage. Build reports with $match, $group, $project, $sort, $limit and accumulators, and learn why stage order matters.
Expressions: dates, strings and conditionals · Aggregation Pipeline · 18 min
The expression operators you will use every day: time bucketing, string manipulation, type conversion and null handling.
$lookup, $unwind and $graphLookup · $lookup & Joins · 22 min
Join collections inside a pipeline, correlate with sub-pipelines, walk hierarchies with $graphLookup, and know when a join means your schema is wrong.
$facet, $bucket, window functions, $merge and $out · Advanced Aggregation · 25 min
Multi-faceted search results, histograms, running totals and rankings, and materialized views that refresh incrementally.
Window functions with $setWindowFields · Advanced Aggregation · 25 min
Running totals, moving averages, rankings and period-over-period deltas computed over ordered partitions, without collapsing documents the way $group does.
$unionWith, $densify and $fill · Advanced Aggregation · 22 min
Combine documents from several collections into one pipeline, add the missing time slots to a series, and fill the gaps with a constant, the last known value or a straight line…
Embedding vs referencing · Schema Design · 25 min
Design for how the application reads and writes. Learn the rules of thumb for embedding versus referencing based on relationship cardinality, growth and access patterns.
Indexes: COLLSCAN vs IXSCAN · Indexes & explain() · 25 min
What an index is physically, how a query uses it, and how to read explain() output to see whether it did.
Reading explain() plans like a DBA · Indexes & explain() · 20 min
Go beyond COLLSCAN vs IXSCAN: SORT stages, rejected plans, index bounds, and the verbosity modes.
Compound indexes and the ESR rule · Compound Indexes & ESR · 30 min
Order the fields of a compound index as Equality, then Sort, then Range. Learn prefixes, covered queries and why one good compound index beats three single-field ones.

Level 3: Advanced

Transactions, concerns, change streams, validation, time series.

Patterns for read performance: computed, subset, extended reference, bucket, outlier · Schema Design Patterns · 30 min
The schema design patterns that turn expensive reads into cheap ones by doing work at write time or by storing data in the shape it is read.
Patterns for flexibility: polymorphic, attribute, versioning, trees, archive · Schema Design Patterns · 25 min
Model varied shapes in one collection, index arbitrary attributes, evolve schemas without downtime, store hierarchies, and age out cold data.
GridFS and storing large files · Schema Design Patterns · 20 min
GridFS stores files larger than the 16 MB document limit by splitting them into chunks across two collections. Learn the layout, the indexes, how to check integrity, and when…
Schema anti-patterns and tree structures · Schema Design Patterns · 26 min
The six schema anti-patterns from the MongoDB manual, how to detect each one on a running database, and the five ways to store a hierarchy: parent references, child references, an…
Unique, partial, sparse, TTL, text, wildcard, hashed and geo indexes · Index Types & Options · 28 min
Every index type and option, what it is for, and the traps in each.
Wildcard indexes for unpredictable fields · Index Types & Options · 18 min
Index every field under a path (or the whole document) when the queried fields are not known in advance, and understand the trade-offs versus the attribute pattern.
Geospatial queries: 2dsphere, $near, $geoWithin and $geoNear · Index Types & Options · 22 min
Store locations as GeoJSON, index them with 2dsphere, and answer nearest-store, within-radius and inside-polygon questions with correct units.
The slow query workflow: profiler, logs, explain, fix · Query Optimization · 28 min
A repeatable process for finding the queries that matter, diagnosing them, fixing them and proving the fix, as practised by DBAs on production systems.
Multi-document transactions · Transactions · 28 min
ACID across documents and collections: sessions, the callback API, retries, write conflicts, limits and when not to use transactions.
Write concern, read concern and read preference · Read & Write Concerns · 28 min
Tune durability, consistency and routing per operation: w and j, local/majority/snapshot/linearizable reads, primary/secondary routing and causal consistency.
Change streams and resume tokens · Change Streams · 22 min
Subscribe to inserts, updates, replaces and deletes in real time, filter them with a pipeline, and resume reliably after failures.
Schema validation with $jsonSchema · Schema Validation · 20 min
Enforce required fields, types, ranges and enumerations on the server, and roll validation out safely with validationLevel and validationAction.
Time series, capped collections, TTL and views · Time Series & Special Collections · 22 min
Purpose-built collection types: time series for measurements, capped for fixed-size logs, TTL for expiry, views for reusable read-only pipelines.
Views, on-demand materialized views and collation · Time Series & Special Collections · 20 min
Expose filtered or reshaped data through read-only views, precompute heavy reports with $merge, and make string matching and sorting language-aware and case-insensitive with…
Clustered collections · Time Series & Special Collections · 18 min
A clustered collection stores documents in _id order inside the _id index itself. Range reads on _id get faster, there is no separate _id index to maintain, and TTL can delete by…

Level 4: Database Engineer

WiredTiger, replica sets, oplog, backup, security, monitoring.

WiredTiger: cache, eviction, checkpoints and the journal · WiredTiger Storage Engine · 30 min
How a write travels from a client to disk, why cache pressure is the root of many incidents, and which metrics tell you the storage engine is struggling.
Maintenance and data checks: validate, compact, renameCollection and $redact · WiredTiger Storage Engine · 24 min
Check a collection and its indexes for corruption, get disk space back after large deletes, swap collections safely with renameCollection, and produce redacted copies of sensitive…
Replica sets, elections and failover · Replica Sets & Elections · 32 min
How members replicate, how a new primary is elected, what priorities, votes, hidden and delayed members do, and how failover looks from the application.
The oplog, initial sync, lag and rollback · Oplog & Replication · 28 min
The capped collection at the heart of replication: what entries look like, how big it should be, what causes replication lag and how rollback works.
Backup, restore and point-in-time recovery · Backup & Restore · 30 min
Logical versus physical backups, consistent snapshots, oplog-based point-in-time recovery, and the restore drills that prove it all works.
Percona Backup for MongoDB: logical, physical and PITR · Backup & Restore · 25 min
Run consistent backups of replica sets and sharded clusters with PBM, enable point-in-time recovery from oplog slices, and rehearse restores.
Security: authentication, RBAC, TLS and encryption · Security · 28 min
Harden a self-managed deployment: enable auth, least-privilege roles, TLS everywhere, internal authentication, encryption at rest, field-level encryption and auditing.
Client-side field level encryption and Queryable Encryption · Security · 22 min
Encrypt sensitive fields in the driver so the server, backups and DBAs only ever see ciphertext, and know what you can still query.
LDAP, Kerberos and x.509 authentication · Security · 24 min
Connect self-hosted MongoDB to corporate identity: authenticate users against LDAP or Kerberos, map directory groups to MongoDB roles, and use x.509 certificates for services.…
Monitoring and diagnostics · Monitoring & Diagnostics · 30 min
The metrics that matter, how to read serverStatus, currentOp, logs and FTDC, and a triage order for incidents.
Monitoring with Percona Monitoring and Management (PMM) · Monitoring & Diagnostics · 20 min
Deploy PMM Server and agents, add MongoDB services with the right user, and use the dashboards and Query Analytics to find bottlenecks.
Server logs: structured JSON, verbosity and log rotation · Monitoring & Diagnostics · 22 min
mongod writes one JSON document per log line. Learn to read the fields, find slow queries and errors, raise verbosity for one component without flooding the disk, and rotate logs…
Rolling upgrades and featureCompatibilityVersion · Upgrades & FCV · 22 min
Upgrade replica sets and sharded clusters without downtime, use FCV as the safety latch, and plan the rollback path.

Level 5: Database Architect

Sizing, drivers and pooling, production tuning, HA/DR, Kubernetes.

Capacity planning: working set, RAM, disk and IOPS · Capacity Planning & Sizing · 28 min
Estimate the hardware a workload needs, from document counts and access patterns to RAM for the working set, disk for growth and IOPS for writes.
Drivers, connection pools, timeouts and retries · Drivers & Connection Pooling · 26 min
Configure the application side correctly: one client per process, pool sizing, server selection and timeouts, retryable writes, and avoiding connection storms.
Production host tuning: OS, filesystem, memory and limits · Production Tuning · 22 min
The operating system settings from the production notes that prevent latency spikes and outages on self-managed hosts.
HA, DR and multi-region topologies · HA, DR & Multi-Region · 30 min
Design for data-centre and region failures: member placement, majority math, disaster recovery runbooks, forced reconfiguration and RPO/RTO trade-offs.
MongoDB on Kubernetes with operators · MongoDB on Kubernetes · 28 min
Run replica sets and sharded clusters on Kubernetes: operators, StatefulSets, storage, scheduling, networking, backups and day-2 operations.
Percona Operator for MongoDB in practice · MongoDB on Kubernetes · 25 min
Deploy replica sets and sharded clusters with the PerconaServerMongoDB custom resource, wire in PBM backups, and run day-2 operations safely.
How to answer MongoDB interview questions · Interview Preparation · 20 min
A structure for technical answers, what interviewers listen for at each level, and how to use the rest of this site to prepare.

Level 6: Sharding / Distributed

Sharded clusters, shard keys, balancer, resharding, migrations.

Sharded cluster architecture and query routing · Sharding Architecture · 28 min
mongos routers, the config server replica set and shards; how queries are targeted or broadcast, and what changes for applications.
Choosing a shard key: cardinality, frequency, monotonicity · Shard Keys · 32 min
The decision that is hardest to change. Evaluate candidate keys against write distribution, query targeting and growth, and compare hashed, ranged and compound keys in the…
Chunks, balancer, zones and orphans · Chunks, Balancer & Resharding · 25 min
How data moves between shards, how to control when it moves, how to pin data to locations with zones, and what orphaned documents are.
Sharding operations in 7.0 and 8.0 · Chunks, Balancer & Resharding · 26 min
How sharded clusters are run today: the balancer by data size, no automatic splitting, the AutoMerger and defragmentation that keep the chunk count low, moving and unsharding…
Cluster migrations and cutover · Cluster Migrations · 25 min
Move data between clusters, versions, topologies or data centres with minimal downtime: dump/restore, replica set extension, mongosync and CDC-based approaches, with validation…

Level 7: Search + Vector

Text search, vector search and RAG patterns with MongoDB.

Text indexes, $text and full-text search engines · Text Search · 22 min
Keyword search with the built-in text index (stemming, stop words, phrases, negation, weights) and when you need a Lucene-based search engine instead.
Vector search and RAG with MongoDB · Vector Search & RAG · 30 min
Store embeddings next to your documents, index them for approximate nearest neighbour search, combine semantic similarity with filters, and build retrieval-augmented generation.