PostgreSQL vs. SQLite

The key differences and advantages of each

If you're in a position to select an RDBMS for a project or just curious to learn more about the differences between PostgreSQL and SQLite, this article will help you understand the key differences between the two. They are both powerful but shine for quite different use cases and are philosophically very different in their designs.

Architecture

PostgreSQL is a client-server database system where you'd set up a server (or use an existing one) that could be on a completely different server than the client that accesses the data. This architecture enables PostgreSQL to scale and handle multiple concurrent clients efficiently, making it well-suited for applications with high volumes of data and complex queries. A key factor in PostgreSQL's concurrency model is its use of Multi-Version Concurrency Control (MVCC), which ensures that readers and writers do not block each other. By maintaining multiple versions of data, MVCC allows transactions to execute concurrently while preserving data consistency and isolating changes until committed. This design is particularly advantageous in high-traffic, multi-user environments where concurrent reads and writes are common.

On the other hand, SQLite is a serverless database engine. It functions as a lightweight library embedded directly into applications, reading and writing data from a single file on disk. This simplicity eliminates the need for a separate server process and makes SQLite highly portable. However, SQLite's concurrency model is more restrictive: while it allows multiple readers, only one process can write to the database at a time. This limitation makes SQLite less suitable for write-heavy or high-concurrency applications, although it remains a strong choice for lightweight, single-user, or read-heavy workloads.

Features

One of the most notable differences between SQLite and Postgres is that SQLite has a simpler feature set, including fewer data types, fewer functions, and fewer advanced SQL features. This makes SQLite easier to use for simple applications but can be limiting for more complex applications that need advanced features.

One notable attribute of SQLite is that it uses "dynamic typing" for data types, which means that you can store any type of data in any column. SQLite will automatically convert it to the appropriate type, when possible, based on the type affinities assigned to a column. If it can't be converted, the value is stored as is. This can be convenient for simple applications but can lead to unexpected behavior if you're not careful about validating data on the application side.

The SQLite type affinities are:

1. TEXT
2. NUMERIC
3. INTEGER
4. REAL
5. BLOB

Any type of data you want to store in SQLite, whether it be boolean, dates, etc., has to fit into those types. That said, SQLite does offer quite a lot of flexibility in terms of what you can do with those data types and how you can manipulate them, but this design can make it difficult to enforce data integrity and consistency with a lot of complicated data.

PostgreSQL is a feature-rich database system that supports advanced features like full-text search, JSON, and XML data types. It also has a rich set of functions and operators for working with data. It also supports advanced SQL features that SQLite does not, like window functions and recursive queries. Of course, many applications don't need all these features, but if you do, PostgreSQL is a great choice.

Additionally, PostgreSQL is designed to be strictly SQL-compliant, which means that it enforces strict data types and constraints and is designed to ensure data integrity and consistency. This makes it great for applications that need to ensure that their data is always in a consistent state. This also can make Postgres appealing in scenarios where strict SQL compliance is a requirement.

Postgres is quite extensible by virtue of its extension system, which allows you to add additional features to the database, like full-text search, GIS capabilities (via PostGIS), time series data support (via TimescaleDB), and more. This makes it great for specialized applications that need advanced features.

Security and Permissions

PostgreSQL has a rich set of security features that allow you to control who can access what data and what they can do with it. You can create users and roles and assign permissions to them to control who can read, write, and delete data in the database. You can also use row-level security policies to control access to individual rows in a table. Additionally, TLS encryption is usually used for client-server connections, and you can configure PostgreSQL to use SSL certificates for authentication.

SQLite has a much simpler model, where everything is in a single file. While you can set file permissions to control access to the raw database, there is no built-in support for user accounts, roles, or permissions. This makes SQLite great for single-user applications but can be limiting for multi-user applications that need to control access to data.

Licensing

Both database types are open-source and generally free to use. For those who are concerned with or interested in software licensing, it's worth noting that SQLite is released under the Public Domain, which means you can use it for any purpose without restriction. That said, a small dedicated team maintains the SQLite project and does not accept unsolicited contributions from the public.

PostgreSQL is released under the PostgreSQL License, which is a permissive open-source license that allows you to use, modify, and distribute the software for free. You can use PostgreSQL in commercial applications without paying any licensing fees.

Why use SQLite over PostgreSQL?

Given that PostgreSQL is a more feature-rich database system that scales in more scenarios, you might be wondering why you would ever use SQLite in the first place. But there are times when SQLite is actually a great choice. Here are some of the reasons it makes sense for certain applications:

1. Portability: SQLite is a single file that you can copy and move around, making it great for applications that need to be portable. You can even run it off a USB stick.

2. Ease of use: SQLite is simple to set up and use and doesn't require a separate server process. This makes it great for small applications or prototyping.

3. Low resource usage: SQLite is lightweight and doesn't require much memory or CPU to run, making it great for embedded systems or applications that need to run on low-powered hardware.

4. Single-user applications: SQLite is great for applications that only need one user to read and write to the database at a time. This makes it great for desktop applications or mobile apps that don't need to scale to many users.

5. Mostly read-only applications: SQLite databases can contain terabytes of data but are limited to a single writer at a time. This makes it great even for large databases used in read-heavy applications that don't need to write to the database frequently. In these cases, especially for small to mid-sized databases, SQLite may be faster than client-server database systems like PostgreSQL since it has minimal overhead and doesn't need to communicate over a network.

Why use PostgreSQL over SQLite?

On the other hand, there are many scenarios where PostgreSQL is going to make more sense than SQLite. Here are some of the reasons you might choose PostgreSQL:

1. Scalability: PostgreSQL is designed to handle high volumes of data and many clients reading and writing to it at once. If you need to scale your application to many users, PostgreSQL is a great choice.

2. Advanced features: PostgreSQL has a rich set of features that make it great for complex applications that need advanced SQL features, like full-text search, JSON, and XML data types, and advanced SQL features like window functions, and recursive queries.

3. Data integrity and consistency: PostgreSQL is designed to enforce data integrity and consistency, with features like many strict types, foreign key constraints, check constraints, and triggers. If you need a wide variety of data types and must ensure that your data is always in a consistent state, PostgreSQL is a great choice.

4. Performance for large datasets: PostgreSQL is designed to be fast and efficient and can be tuned to perform well in a wide variety of scenarios. If you need a database that can handle complex queries and high volumes of data, PostgreSQL is a great choice.

5. Specialized and scientific applications: Compared to other popular RDBMSes like MySQL, PostgreSQL has more data types and more advanced features like JSONB columns, array types, range types, etc., that make it great for specialized applications like scientific research, GIS (especially with the PostGIS extension), and other fields that need advanced data types and features.

6. Granular security and permissions: PostgreSQL has a rich set of security features that allow you to control who can access what data and what they can do with it. If you need fine-grained control over your data for many users, PostgreSQL can offer this.

Summary

PostgreSQL and SQLite are both powerful database systems based on SQL but are fundamentally quite different in their design. PostgreSQL is a client-server database system that is designed to handle high volumes of data and complex queries and is great for complex applications that need to scale to many users. SQLite is a serverless database engine that is lightweight and portable and is great for small or local applications that need to be portable or for applications that only need one user to read and write to the database at a time.

Here's a simple table showing some of the strengths and weaknesses of each:

Feature/Requirement	SQLite	PostgreSQL
Architecture	File-based	Client-server
SQL Compliance	Loose	Strict
Concurrency	Single writer	High concurrency
Backup & Replication	Basic Backup, Hot Backups	Advanced replication options
Security	Basic	Advanced
Ideal Use Cases	Embedded, lightweight apps	Complex, scalable applications