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Cassandra vs MongoDB

Cassandra logo

Cassandra

Software

Manage massive amounts of data with linear scalability

From
Free
Rated
-
Full reviewWebsite
MongoDB logo

MongoDB

Software

The developer data platform

From
Free
Rated
-
Full reviewWebsite

The short version

  • Each has a real cost: Cassandra no support for joins across tables; MongoDB 16 MB maximum document size limits large single objects
  • They diverge on capability: Cassandra covers Linear Scalability, MongoDB covers Document model.

Where they differ

Only the attributes on which Cassandra and MongoDB actually diverge.

Attributes where Cassandra and MongoDB differ
AttributeCassandraMongoDB
PlatformsLinux, macOS, Windows, Docker, KubernetesCloud (Atlas), Self-hosted, Multi-cloud (AWS, Google Cloud, Azure)
Founded20082007

Identical on both: starting price (Free), pricing model (Unknown), free tier (Yes), user rating (Not yet rated), category (Unknown).

What each one covers

Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.

Only in Cassandra

  • Linear Scalability
  • Fault Tolerance
  • Multi-datacenter Replication
  • Tunable Consistency
  • CQL Query Language
  • Distributed Architecture
  • No Single Point of Failure
  • DataStax

Only in MongoDB

  • Document model
  • Distributed architecture
  • ACID transactions
  • Real-time analytics
  • Full-text search
  • Time series data
  • Geospatial queries
  • Aggregation framework

What people use each for

The jobs each tool is most often brought in to do.

Cassandra

  • Real-time applicationsnot MongoDB
  • Content management
  • User profilesnot MongoDB
  • Mobile backendsnot MongoDB
  • Cachingnot MongoDB

MongoDB

  • Mobile applicationsnot Cassandra
  • Content management
  • Real-time analyticsnot Cassandra
  • IoT applicationsnot Cassandra
  • Gaming backendsnot Cassandra

Both are used for content management, on those jobs the choice comes down to price and fit rather than capability.

Where each one falls short

Documented limitations, not opinions. Every one is a constraint you would hit in normal use.

Cassandra

  • No support for joins across tables
  • No ACID transactions across multiple rows
  • Data model must be designed around query patterns upfront, making schema evolution difficult
  • Partition key misconfigurations can cause uneven data distribution and hotspots that degrade performance

MongoDB

  • 16 MB maximum document size limits large single objects
  • No native JOIN support for relational data operations
  • Higher memory usage due to storing field names with each document
  • Eventual consistency in distributed deployments can cause data stale reads

Pricing, plan by plan

Cassandra

Free

No published plan breakdown. See the Cassandra review.

MongoDB

Free
  • M0Free
    • 512 MB storage
    • Learning and exploration
  • M2$9/month
    • 2 GB storage
    • Development and testing
  • M5$25/month
    • 5 GB storage
  • M10+$56.94/month
    • Dedicated clusters for production

Which should you pick?

Choose Cassandra if

  • You need linear scalability.
  • You want to start without paying.
  • You work on Linux, macOS, Windows, Docker, Kubernetes.
  • You also want fault tolerance.
Cassandra review

Choose MongoDB if

  • You need document model.
  • You want to start without paying.
  • You work on Cloud (Atlas), Self-hosted, Multi-cloud (AWS, Google Cloud, Azure).
  • You also want distributed architecture.
MongoDB review

Questions people ask

Is Cassandra or MongoDB better?
Neither clearly leads. Cassandra starts at Free and MongoDB at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, Cassandra or MongoDB?
Cassandra starts at Free and MongoDB at Free.
Does Cassandra or MongoDB run on more platforms?
Cassandra runs on Linux, macOS, Windows, Docker, Kubernetes. MongoDB runs on Cloud (Atlas), Self-hosted, Multi-cloud (AWS, Google Cloud, Azure).
Can I use Cassandra for free?
Both have a free tier, so you can try either at no cost before committing.
What is Cassandra best used for?
Cassandra is most often used for real-time applications, content management, user profiles, mobile backends. Of those, real-time applications and user profiles are not what MongoDB is typically brought in for.
What can Cassandra do that MongoDB cannot?
Cassandra covers Linear Scalability, Fault Tolerance, Multi-datacenter Replication, Tunable Consistency. MongoDB covers Document model, Distributed architecture, ACID transactions, Real-time analytics.

Answered from the vendors’ own pages

Cassandra: Does Cassandra support joins between tables?

No. Cassandra does not support joins or foreign keys. The data model requires denormalization, meaning data must be duplicated across tables to support different query patterns.

Source
MongoDB: Does MongoDB offer a free tier?

Yes. MongoDB Atlas offers an M0 free tier with 512 MB storage for learning and exploration, plus paid options starting at $9/month for M2 with 2 GB storage.

Source
Cassandra: Does Cassandra offer ACID transactions?

No. Cassandra provides only row-level atomicity and isolation, not full ACID transactions across multiple rows or tables. It uses lightweight transactions via Paxos for per-row compare-and-set operations.

Source
MongoDB: Can I self-host MongoDB?

Yes. You can run MongoDB Community Edition on your own servers, or use MongoDB Enterprise Advanced for self-managed production deployments with enterprise features.

Source
Cassandra: What programming languages can connect to Cassandra?

Cassandra supports official drivers for multiple languages including Python, Java, Node.js, and Go, allowing applications to communicate via the native Cassandra protocol.

Source
MongoDB: What is the maximum document size in MongoDB?

Documents are limited to 16 MB. For documents exceeding this limit, you can use MongoDB's GridFS API to store files larger than the maximum size.

Source
Cassandra: Can I deploy Cassandra in the cloud?

Yes. Cassandra can run on any cloud platform (AWS, Google Cloud, Azure) via Docker, virtual machines, or managed services like DataStax Astra DB, which provides a fully managed DBaaS option.

Source
MongoDB: Does MongoDB support ACID transactions?

Yes. MongoDB supports ACID transactions within a single document by default, and multi-document ACID transactions are available for replica sets and sharded clusters in MongoDB 4.0+.

Source
Cassandra: Does Cassandra have a free option?

The open source Apache Cassandra is free. DataStax also offers Astra DB with a free tier providing up to 25GB storage and 25 million read/write operations per month.

Source
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