MongoDB vs. PostgreSQL – The 5 Big Differences

MongoDB and PostgreSQL are popular data providers with a wide range of features that make them ideal for various applications. When considering which database technology is right for your business, it’s important to understand the major differences between them.

To help you decide which one is best for your needs, let’s dive into what MongoDB and PostgreSQL are. Alongside its key features, we’ll look at 5 major differences between the two.

What Is MongoDB and Its Key Features

MongoDB is a versatile, open-source NoSQL database. It stores data in dynamic JSON-like documents and supports easy query, manipulation, and storage of data.

Its key features include:

• Automatic sharding: MongoDB’s automatic shading feature allows for horizontal scaling of data across multiple servers. This enables efficient processing of large datasets, as each shard processes only the relevant portion of data for a query.
• Flexible indexing: MongoDB’s indexing system is highly flexible and allows for efficient querying of large datasets. Indexes can be created on any field within a document and can include geospatial indexes for location-based queries.
• Ad hoc queries: MongoDB atlas supports ad hoc queries, which means that developers can query data in real time without having to predefine the schema or structure of the data. This allows for greater flexibility and faster iteration.
• Powerful aggregation framework: MongoDB’s aggregation framework provides a powerful set of tools for complex data analysis and manipulation. It includes support for grouping, sorting, and filtering data, as well as running mathematical and statistical operations.
• Data validation: MongoDB allows for the validation of data before it is inserted into the database. Therefore, ensuring data quality and consistency across the application.
• Querying and indexing of JSON data: MongoDB stores data in JSON format, making it easy to work with for developers who are already familiar with the syntax. Additionally, it supports querying and indexing of JSON data for fast and efficient data access.

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What Is PostgreSQL and Its Key Features

When discussing databases, it’s important to consider PostgreSQL as a counterpart to MongoDB. Like MongoDB, PostgreSQL is an open-source database system, but it is an object-relational database. This means that it stores data in tables with rows and columns and supports SQL for communicating with the database.

PostgreSQL is known for its powerful features:

• Complex joins: PostgreSQL provides support for complex joins, allowing developers to combine data from multiple tables with ease. This makes it easier to manage and query large datasets.
• Foreign keys: PostgreSQL supports the use of foreign keys, which allows developers to enforce referential integrity between related tables. This ensures data accuracy and consistency.
• Transactions: PostgreSQL supports transactions, which are essential for ensuring data integrity in multi-user environments. This means that multiple users can access the database at the same time without compromising data consistency.
• Large dataset handling: PostgreSQL is designed to handle large datasets efficiently, making it a great choice for applications that require the management of vast amounts of data.
• Robust SQL support: PostgreSQL provides robust support for SQL, including support for advanced SQL features such as Common Table Expressions (CTEs) and window functions. This makes it a powerful tool for complex data analysis and manipulation.

Comparing MongoDB with PostgreSQL

Let’s look at five of the biggest differences between MongoDB and PostgreSQL, that you should consider when deciding which database to use.

Database structure

MongoDB is a non-relational database that stores data in dynamic JSON-like documents, while PostgreSQL is an object-relational database that stores data in pre-defined tables with rows and columns. MongoDB does not require a pre-defined schema before inserting data, whereas PostgreSQL does.

To better illustrate with an example,

Suppose you are building an e-commerce website and you need to store information about products, such as their name, description, price, and availability.

In MongoDB, you could simply insert a document containing all the necessary information for each product, without having to define a schema beforehand. For example, a product document in MongoDB could look like this:
{
"name": "Product A",
"description": "A great product",
"price": 99.99,
"available": true
}


On the other hand, in PostgreSQL, you would need to define a schema for the products table before inserting any data. For example, you could define a schema like this:

CREATE TABLE products (
id SERIAL PRIMARY KEY,
name VARCHAR(255) NOT NULL,
description TEXT NOT NULL,
price DECIMAL(10, 2) NOT NULL,
available BOOLEAN NOT NULL
);


Query Language

1. 1. MongoDB uses the Mongodb Query Language (MQL) to query data from documents within collections, while PostgreSQL uses the Structured Query Language (SQL) to query data within tables.
   2. Consider a collection of customer orders in a MongoDB database, where each order is represented as a document with fields such as customer name, order date, and items purchased.
   3. To retrieve all orders placed by a specific customer, we can use MQL to write a query like this:


db.orders.find({ customer_name: "John Doe" })


1. 1. On the other hand, in a PostgreSQL database, we might have a table called “orders” with columns such as order_id, customer_name, order_date, and item_name. To retrieve all orders placed by a specific customer, we can use SQL to write a query like this:


SELECT * FROM orders WHERE customer_name = 'John Doe';


Data Modification

1. 1. MongoDB allows for deeply modifying its documents through dot notation and dynamic updates. Whereas in PostgreSQL, such modifications require complex queries involving joining multiple tables.
   2. For example, let’s say we have a MongoDB document representing a user:


{
_id: ObjectId("61706be733b3a3b47fd8d0cf"),
firstName: "John",
lastName: "Doe",
address: {
street: "123 Main St",
city: "Anytown",
state: "CA",
zip: "12345"
}
}


1. 1. We can easily update the user’s city with a single update command:


db.users.updateOne({_id: ObjectId("61706be733b3a3b47fd8d0cf")}, {$set: {"address.city": "Newtown"}})


1. 1. On the other hand, in PostgreSQL, if we had a similar data model split across multiple tables, we would need to join them and run a complex query to update the user’s city:


UPDATE users
SET address_city = 'Newtown'
FROM users
INNER JOIN addresses ON users.address_id = addresses.id
WHERE users.id = 1;


Database Scalability

1.  MongoDB supports horizontal scalability through sharding, which allows for distributing data across multiple servers.  PostgreSQL also supports horizontal scalability through sharding, but it requires more setup effort than MongoDB. Replication is another way to scale horizontally in PostgreSQL, where data is copied across multiple servers for load balancing and high availability.
2. Suppose an e-commerce website has a large customer database, and the company wants to ensure that the database can handle increased traffic during peak hours. If they use MongoDB, they can shard the customer data across multiple servers, ensuring that each server handles a portion of the customer data. On the other hand, if they use PostgreSQL, they can also shard the customer data across multiple servers, but it requires more setup effort. Alternatively, they can use replication to copy the customer data across multiple servers for load balancing and high availability.

Security Model

1.  The security models of MongoDB and PostgreSQL differ greatly.  MongoDB offers Role-Based Access Control (RBAC), which restricts access to the database based on predefined roles.
2. PostgreSQL, on the other hand, offers both Row-Level Security (RLS) and Column-Level Security (CLS), which restrict access to specific rows or columns within a table based on predefined security policies.
3. For example, consider a table in a PostgreSQL database containing sensitive financial data.
4. The table may have a column that contains employees’ salaries. With RLS/CLS, the database administrator can define a security policy that restricts access to this column for certain roles or users, such as preventing low-level employees from viewing the salaries of their colleagues. This allows for more fine-grained control over data access, which can be critical for data security and privacy.
5. In contrast, MongoDB’s RBAC is focused on defining roles and permissions at a broader level, such as restricting access to specific collections or databases.

Challenges of Using MongoDB & PostgreSQL

MongoDB

Some of the primary challenges of using MongoDB include:

• Cost: Depending on your use case, using MongoDB can be more costly than using PostgreSQL. This is because MongoDB requires additional functionality such as replication, sharding, and data validation.
• Administration: As with any database, the administration comes with its own set of complexities and difficulties.

PostgreSQL

Some of the primary challenges of using PostgreSQL include:

• Object-Relational Mapping (ORM): ORM can be difficult to implement in some cases as it maps data between SQL and object-oriented programming.
• Performance: Performance may not always be optimal when dealing with large amounts of data or complex queries.
• Security: Although PostgreSQL is a mature database, it still has vulnerabilities. For instance, SQL injection attacks require constant monitoring and protection.

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The Best Option for Your Database Needs

Both MongoDB and PostgreSQL have their own set of features and challenges. Ultimately, the decision comes down to the business use case you are working with and its needs.

Using MongoDB and PostgreSQL in Data Integration

Whether you go for MongoDB or PostgreSQL, Astera Centerprise provides a powerful code-free means for you to natively connect to the database of your choice and use it as part of a data integration pipeline.

The MongoDB Source object in the product lets the user load a MongoDB database of their choice and use it within the scope of an ETL pipeline.

Similarly, Astera Centerprise also allows connectivity to a PostgreSQL instance within the scope of an ETL pipeline. The PostgreSQL connector can be used as both a source to load data from or a destination to load data to.

Depending on the user application, either option can be utilized to work on.

Conclusion

When choosing between MongoDB and PostgreSQL, consider your project’s needs and the benefits of each database engine.

MongoDB offers more flexibility and scalability, while PostgreSQL provides greater security and customization. However, there are many other databases available that may better suit your project’s requirements.

Ultimately, the best choice of a database depends on the specific needs of the project.

Check out our other in-depth MongoDB comparison guides: MongoDB vs. SQL Server, MongoDB vs. MySQL.