Why is Redis so fast?

Redis is incredibly fast and popular, but why so?

Redis is one prime example of an innovative personal solution becoming leading technology used by companies like FAANG. But again, what made it so special?

Salvatore Sanfilippo, also known as antirez, started developing Redis in 2009 while trying to improve the scalability of his startup’s website. Frustrated by the limitations of existing database systems in handling large datasets efficiently, Sanfilippo wrote the first version of Redis, which quickly gained popularity due to its performance and simplicity.

Over the years, Redis has grown from a simple caching system to a versatile in-memory data platform, under the stewardship of Redis Labs, which continues to drive its development and adoption across various industries.

Now let’s address the popularity part of it:

Redis's rise to extreme popularity can be attributed to several key factors that made it not just a functional tool, but a revolutionary one for database management and caching. Let’s get into the details:

➡️ Redis is renowned for its exceptional performance, primarily due to its in-memory data storage. By storing data directly in RAM, Redis can read and write data at speeds much faster than databases that rely on disk storage. This capability allows it to handle millions of requests per second with sub-millisecond latency, making it ideal for applications where response time is critical.

➡️ Redis is simple to install and set up, with a straightforward API that makes it easy to integrate into applications. This ease of use is a major factor in its popularity, as developers can quickly implement Redis to improve their application performance without a steep learning curve.

➡️ Unlike many other key-value stores, Redis supports a variety of data structures such as strings, lists, sets, hashes, sorted sets, bitmaps, and geospatial indexes. This variety allows developers to use Redis for a wide range of use cases beyond simple caching, including message brokering, real-time analytics, and session management.

➡️ Redis is not just a cache. It's versatile enough to be used as a primary database, a caching layer, a message broker, and a queue. This flexibility has enabled it to fit into various architectural needs, making it a popular choice among developers working on complex applications.

➡️ Being open source has allowed Redis to benefit from contributions from a global developer community, which has helped in enhancing its features and capabilities over time. The community also provides a wealth of plugins, tools, and client libraries across all programming languages, which further enhances its accessibility and ease of use.

Not only that Redis Labs, the home of Redis, continuously innovates and adds new features to meet the evolving needs of modern applications. But also Redis has been adopted by tech giants such as Twitter, GitHub, Snapchat, Craigslist, and others, which has significantly boosted its profile.

Why is Redis so-incredibly fast?

Now that we have understood the popularity of Redis, let’s look into the technicalities which makes it incredibly faster, even after being a single-threaded app.

1. In-Memory Storage

The primary reason for Redis's high performance is its in-memory data store. Unlike traditional databases that perform disk reads and writes, Redis operates entirely in RAM. Data in RAM is accessed significantly faster than data on a hard drive or an SSD.

2. Data Structure Optimization

Redis supports several data structures like strings, hashes, lists, sets, and sorted sets, each optimized for efficient access and manipulation. For instance, adding an element to a Redis list is an O (1) operation, meaning it executes in constant time regardless of the list size.

3. Single-Threaded Event Loop

Redis uses a single-threaded event loop to handle all client requests. This design simplifies the processing model and avoids the overhead associated with multithreading (like context switching and locking). Since all commands are processed sequentially, there is never more than one command being processed at any time, which eliminates race conditions and locking delays.

4. Asynchronous Processing

While Redis uses a single-threaded model for command processing, it employs asynchronous operations for all I/O tasks. This means it can perform non-blocking network I/O and file I/O, which lets it handle multiple connections without waiting for operations to complete.

5. Pipelining

Redis supports pipelining, which allows clients to send multiple commands at once, reducing the latency costs associated with round trip times. This is particularly effective over long distances where network latency can significantly impact performance.

6. Built-In Replication and Clustering

For scalability, Redis offers built-in replication and support for clustering. This allows Redis instances to handle more data and more operations by distributing the load across multiple nodes, each of which can be optimized for performance.

7. Lua Scripting

Redis allows the execution of Lua scripts on the server side. This feature lets complex operations be processed on the server in a single execution cycle, avoiding multiple roundtrips and decreasing processing time.

8. Persistence Options

Redis provides different options for data persistence, allowing it to balance between performance and durability requirements. For example, the Append Only File (AOF) can be configured to append each operation to a log, which can be synchronized with the disk at different intervals according to the desired durability level.

Redis's design choices directly contribute to its speed, making it a preferred option for scenarios requiring rapid data access and modification. Its ability to support high throughput with low latency is a key factor behind its widespread adoption in industries where performance is critical.