PostgreSQL vs MongoDB: Which Database Should Your App Use?

PostgreSQL vs MongoDB is one of the first choices in a new project, and the MERN stack taught many developers in India to reach for MongoDB by default. Both are mature, widely used and easy to host. They store data in different shapes, and that shape decides how easy your app is to build and change a year from now. This guide compares them on the points that matter in practice, with the real limits, licences and costs, and shows the same query written for each.

Tables or documents

PostgreSQL stores data in tables with a defined set of columns. An order lives in an orders table, its items in an order_items table, and foreign keys link them. One SQL query joins them back together.

MongoDB stores JSON-like documents in collections. An order and its items can sit in one document, and two documents in the same collection may have different fields, so you can change the shape without a migration.

Neither is better in general. Documents are natural when you always read and write the whole thing together. Tables are natural when the same data is used from many directions, such as an order seen from the customer, the product and the warehouse.

The two engines compared point by point

The MongoDB figures are from its official limits and thresholds reference.

The same question, asked of each

“The ten biggest orders this week, with the customer’s name”:

SELECT o.id, c.name, o.total
FROM orders o
JOIN customers c ON c.id = o.customer_id
WHERE o.created_at > now() - interval '7 days'
ORDER BY o.total DESC
LIMIT 10;

db.orders.aggregate([
  { $match: { createdAt: { $gt: new Date(Date.now() - 7 * 864e5) } } },
  { $sort: { total: -1 } },
  { $limit: 10 },
  { $lookup: { from: "customers", localField: "customerId", foreignField: "_id", as: "customer" } },
  { $project: { total: 1, "customer.name": 1 } }
]);

Both work. The SQL version stays short as the question grows; the pipeline grows a stage for every new relationship. Many MongoDB designs avoid $lookup by copying the customer’s name into each order, which makes this read fast and makes renaming a customer a write to every order they ever placed.

Transactions and correctness

PostgreSQL has had full ACID transactions across any number of tables since its early versions. Money, inventory and bookings, where two writes must succeed or fail together, fit it naturally.

MongoDB has always made a single document update atomic, and has supported multi-document transactions since version 4.0. They work, but they were added to a design built around single documents: they cost more, and by default a transaction that runs longer than 60 seconds is aborted. Many MongoDB apps avoid them by putting everything that changes together into one document.

JSON in PostgreSQL

You do not have to give up documents to use PostgreSQL. Its jsonb type stores JSON in a column, can be indexed, and can be queried in the same statement as normal columns:

CREATE TABLE products (
  id bigserial PRIMARY KEY,
  name text NOT NULL,
  price numeric NOT NULL,
  attributes jsonb
);
CREATE INDEX ON products USING gin (attributes);

SELECT name, price FROM products WHERE attributes @> '{"colour": "black"}';

A common pattern is typed columns for what every row has, plus a jsonb column for optional fields. PostgreSQL’s own JSON types documentation covers the operators. For heavy, deeply nested documents that change shape constantly, MongoDB is still more comfortable.

Licences: why some companies care

PostgreSQL uses a short, permissive licence approved by the Open Source Initiative. You can use, change and offer it as a service with almost no conditions.

MongoDB moved to the Server Side Public License in 2018. It is free to use in your own app, but it adds strict conditions if you offer MongoDB itself as a service, and it is not OSI-approved. Some Linux distributions and projects dropped MongoDB over this. For most app developers it changes nothing; for a company building a database product, it matters.

Popularity

PostgreSQL was the most used database in the 2023, 2024 and 2025 Stack Overflow Developer Surveys. That shows up in practice: more hosting options, more ORM support, and more answers when you get stuck.

Where Supabase fits

Supabase is PostgreSQL, so “Supabase vs MongoDB” is the same choice as PostgreSQL vs MongoDB, plus Supabase’s auth and API on top. We explain what Supabase adds in the Supabase database explained.

Free tiers and costs from India

Atlas figures are from MongoDB’s official pricing page, checked on 7 October 2026. Compare like with like: an Atlas dedicated cluster runs as a three-node replica set, which is part of why it costs more. For PostgreSQL, Voroa’s managed PostgreSQL runs in Mumbai next to the app you deploy from GitHub; all sizes are on the pricing page.

How to choose in one minute

• Your data has clear relationships, you need reports, or money is involved: PostgreSQL.
• Your data is self-contained documents of changing shape, read and written whole: MongoDB.
• You are unsure: start with PostgreSQL and use jsonb for the flexible parts. Moving from PostgreSQL to documents later is easier than the reverse.

FAQ

Is PostgreSQL faster than MongoDB?

It depends on the query. MongoDB is often faster for reading one nested document; PostgreSQL is usually faster for joins, grouping and reports. For most apps, indexes matter far more than the engine.

Can I use PostgreSQL with Node.js and Express?

Yes. Use Prisma, Drizzle, Sequelize or the pg driver; a MERN app becomes a “PERN” app. Deploying it is covered in deploying a Node.js app.

Should a MERN app switch to PostgreSQL?

Only if relationships or transactions are causing real pain. A working app on MongoDB does not need to move. A new app with relational data is easier to start on PostgreSQL.

Is MongoDB still open source?

It is source-available under the SSPL, which the Open Source Initiative does not recognise as an open source licence. You can still use it freely inside your own application.

Start with PostgreSQL in Mumbai

Create a free PostgreSQL database, connect it with one DATABASE_URL, and keep flexible fields in jsonb. The steps are in creating and connecting a database, and the hosted options are compared in our Supabase alternative guide.