If you've participated in many interviews, you've probably heard the question: "What are the differences between NoSQL and SQL databases?" This article will help you clearly understand these differences and when to choose one over the other.
As a software developer, you may have already worked with various SQL databases such as T-SQL, PostgreSQL, MySQL, and others. What's the first thing you've likely noticed? The "rules" or the "schema," of course. SQL databases have highly structured data models. You create tables with defined columns and rows, strictly following a predetermined schema. Breaking this structure means violating the fundamental principles of SQL. Tables, columns, rows, and data types form the essential building blocks for organizing your data.
On the other hand, when you work with NoSQL databases (non-relational databases) like Azure Cosmos DB, Aurora, or MongoDB, you have the flexibility to frequently modify your data model. NoSQL databases don't enforce a rigid structure. They provide an "elastic" schema, allowing you to store data in various formats. Instead of sticking to the traditional table representation, you can use document-based, key-value-based, graph-based, or column-based models, among others.
For relational databases, developers usually apply normalization (such as first normal form, second normal form, etc.) to ensure a clear and balanced data structure. As a result, relational databases often rely heavily on multi-table JOINs, aggregations, and complex relationships to retrieve data. However, when datasets become large, it can be challenging and inefficient to manage and retrieve data quickly from relational databases.
Unfortunately, relational databases aren't inherently designed to handle massive volumes of data. They follow a "scale-up" approach, meaning they require more resources such as RAM, CPU, and GPU to handle increased data.
NoSQL databases, however, are designed for "scaling out." This means you can distribute and handle data across multiple servers without negatively impacting performance. Many people associate "NoSQL" with "Big Data," often using these terms interchangeably. Indeed, you can consider the term "NoSQL" a buzzword frequently associated with solving big data challenges.
Behind NoSQL Lies the 3V Principle
- Volume
- Velocity
- Variety
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Let's examine each of these elements individually to understand their importance.
Volume refers to handling massive datasets, reaching terabytes, petabytes, and beyond. Thanks to the "scale-out" design, NoSQL databases comfortably manage vast amounts of data without issues. SQL databases, by comparison, often struggle with such extensive data sets due to limitations in hardware scaling and structured data constraints, making them less efficient for extremely large data scenarios.
Velocity is about throughput—handling massive amounts of simultaneous requests quickly and efficiently. NoSQL databases excel at processing high-velocity data streams, which is crucial for applications like social media feeds, real-time analytics, IoT applications, and more. SQL databases may experience bottlenecks due to their rigid schemas and transaction overhead, slowing down performance in high-throughput situations.
Variety emphasizes schema flexibility. You can utilize any of the schema forms mentioned previously or even choose a schema-less approach entirely. This schema flexibility means NoSQL databases can easily accommodate rapidly evolving data requirements, different data formats, and unstructured or semi-structured data like images, videos, and sensor data. Conversely, SQL databases are best suited for structured and consistent data that doesn't frequently change.
Let's explore more internal details between them.
- Transactions and ACID Compliance: SQL databases generally offer strong consistency and ACID (Atomicity, Consistency, Isolation, Durability) compliance. NoSQL databases often sacrifice strict ACID compliance for scalability and flexibility, adopting eventual consistency models.
- Complex Queries and Reporting: SQL databases excel in executing complex queries, and multi-table joins, and providing extensive reporting capabilities. NoSQL databases might require additional processing layers or specialized query mechanisms for complex analytical queries.
- Scaling Approaches: SQL databases typically scale vertically (adding more resources to a single server), while NoSQL databases scale horizontally (adding more servers), providing more flexibility and efficiency for handling large datasets.
Understanding these differences and key characteristics will help you choose the right database solution based on your specific requirements. The best measure for your application is your context. The application context defines which one is perfect for you.