Redis as Cache: How it Works and Why to Use it

Redis as Cache

Redis gained very high popularity as being a cache. It is not only fast, but also easy to use. Let us show you why you should use Redis as a cache.

Each of us met the situation when application was working slowly. Even the best code will slow down its performance at high load. Caching can be fast and relatively cheap way to highly increase performance and reduce response time.

What’s Redis

Redis (REmote DIctionary Server) is an open source, in-memory data store that is most often used as a distributed cache. It offers a variety of efficient data structures designed to allow lightning-fast access to your data. Redis is also known as NoSQL Database and key/value store. Because it stores data in memory, rather than on a disk, Redis delivers unparalleled speed, reliability, and performance.

Now, what is the in-memory data store? To put it simply, it is a database that keeps the whole dataset in RAM. It means that each time you query a database or update data in a database, you only access the main memory. So, there’s no disk involved in these operations. And this is great, because the main memory is way faster than any disk.

Why Use Redis as a Cache

The cache’s main purpose is to reduce the time needed to access data stored outside of the application’s main memory space. Without the use of a cache, the application interacts with the data source for every request, whereas when a cache is employed only a single request to the external data source is needed, with subsequent access served from the cache.

When an application relies on external data sources, the latency and throughput of those sources can create a performance bottleneck. One way to improve performance is to store and manipulate data in-memory, physically closer to the application.

This is where Redis comes into play. Redis is built to stores all data in-memory, delivering the fastest possible performance when reading or writing data.

Redis is extremely fast. It delivers sub-millisecond response times that enable millions of requests per second to power demanding real-time applications.

Typically what you’ll want to do is store frequently accessed data in Redis, so that whenever the data is requested it can come from the cache instead of your database. You can then invalidate the relevant cache whenever a change is made to your data so that you can keep your cache up to date.

How Does Redis Cache Work

Let’s say you have a WordPress-based website.

The first time a WordPress page is loaded, a database query is performed on the server. Redis remembers, or caches, this query. So, when another user loads the WordPress page, the results are provided from Redis and from memory without needing to query the database.

An object cache works by caching the SQL queries in memory which are needed to load a WordPress page. When a page loads, the resulting SQL query results are provided from memory by Redis, so the query does not have to hit the database. The result is much faster page load times, and less server impact on database resources.

How does Redis work

It’s way faster to access data in memory (physical RAM) than to access data in the hard drive. So it’s easy to notice that if the data that the application wants to access is inside the main memory, it’s way easier to reach to that data than if it was stored in the Hard Drive.

If a query is not available in Redis, the database provides the result and Redis adds the result to its cache. If a value is updated in the database (for example, a new post or page is created in WordPress) the Redis value for that query is invalidated to prevent bad cached data from being presented.

Why to Use Redis

  • Quick response database: it stores data in memory, rather than on a disk that’s why its response time is quicker than others when performing read and write operations. Can be used together with other databases as a support to reduce load and improve performance, but can also be used as a primary database.
  • Data persistence: Redis uses persistent disk storage designed to survive process outages and network bottlenecks.
  • Session Cache: One of the most apparent use cases for Redis is using it as a session cache. The advantages of using Redis over other session stores is that Redis offers persistence. 
  • Key-based access: Redis is based on the key-value model in which data is stored and fetched from Redis by key. Key-based access allows for extremely efficient access times and this model maps naturally to caching.

So, we have only scratched the surface of the information available on this topic. For more information on learning Redis, with available resources outlined, you can visit the documentation.

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