Caching: What It Is and How It Works

Learn the basics of caching, its importance, and different types like browser, server-side, and CDN caching.

What is caching?

What do we mean when we say “caching?” Well in layperson’s terms, caching is the secure stashing of information where your computer can get it faster. But let’s take a closer look.

Even the fastest internet connection can be slowed down if, every time you hit the back button, or revisit a page, that data needs to be downloaded from its original source. Caching is a shortcut where frequently accessed data or resources are stored in a temporary storage location where they can be quickly retrieved when it’s needed again. This way, data that’s computationally heavy can be more rapidly called up. 

Whether the cached data is stored in the browser, on the network edge, or on a server, this “trick” accelerates data retrieval to improve your overall system performance. In short, it makes the browsing experience smoother and faster. Because the data in a cache is usually stored in fast-access hardware such as RAM (Random-access memory) or related to a piece of software, its retrieval time can be reduced to a matter of milliseconds. 

Caching has been around since the 1960s when computer memory was extremely limited. Though its nature and technology have changed over the years, caching has remained integral to computing, especially as memory needs have grown. As computers have evolved, caching has kept pace, from early in-processor cache memory to modern web caching techniques that make use of cloud resources.

Why is caching important?

Every time you open a web page after the first time, you experience the benefits of caching. Because the data is stored closer to the user’s device, load times are faster; because the user’s device is not calling on the server for as much data, server load is reduced. Because of these, and because caching involves faster memory transfer, sites and applications run faster and more reliably. 

How does caching work?

There are a few different ways that the “trick” of caching is accomplished. Browser caching stores web page resources locally for faster access. Server-side caching stores data on the server to reduce load times. Content Delivery Network (CDN) caching distributes content across global servers, minimizing latency.

Each optimizes website performance in its own way by reducing data retrieval times and enhancing user experience. Let’s take a closer look at them.

Types of caching 

Browser caching

Browser caching is what most people think of when they think of caching. It involves storing web page resources such as HTML files, images, CSS stylesheets, and JavaScript scripts locally on the user’s device. When a user visits a website for the first time, their browser downloads these resources from the server.

Then, on subsequent visits to the same website the browser checks its cache for these resources before fetching them from the server again. This significantly reduces load times and improves page responsiveness, as the browser can retrieve cached resources quickly without waiting for the server to respond.

Object caching

Object caching involves storing frequently accessed data objects or computation results in memory for faster retrieval by applications. WordPress uses object caching in its content management system (CMS) to cache database queries, API responses, and other dynamic content. By caching objects in memory, applications can avoid the overhead of repeatedly querying databases or executing complex computations, resulting in improved performance and scalability.

Server-side caching

Where browser caching stores frequently used items right on your device, server-side caching holds data that you reuse on the origin server itself. This allows you to retrieve your data more quickly as it is ready for use at the site when needed. It also reduces the compute load on your own device by storing and managing data without using your own memory as browser caching does. It’s a good solution for dynamic sites where the server-side data may change from visit to visit.

Content delivery network (CDN) caching

Content Delivery Networks (CDNs) play a pivotal role in caching by distributing website content across a network of geographically dispersed servers. When you request content from a website that utilizes a CDN, the CDN caches static assets such as images, videos, and other media files on its servers located in strategic locations worldwide.

This distribution enables users to access content from servers closest to their geographical location, reducing latency and improving load times.

Database caching

Database caching involves storing frequently accessed database queries or query results in memory or disk storage to accelerate data retrieval. In high-traffic websites or applications, database queries can become a bottleneck, causing delays in page load times and response rates.

By caching database queries or results, subsequent requests for the same data can be served directly from the cache, bypassing the need for costly database operations.

Tools and technologies

With 43% of the world’s websites built on WordPress, running with VIP gives your enterprise site an enormous selection of tools, technologies, and plugins to help streamline, accelerate, and refine how data is cached. You can browse or search the huge library of free plugins for WordPress on our plugin page. Here are some of the most popular caching tools available now:

Redis: Redis is the #1 cited brand for caching solutions. It provides in-memory data storage to improve performance by reducing database load and speeding up data retrieval.

Cloudflare: A popular CDN and security platform, Cloudflare offers caching services along with security services and performance optimization tools for WordPress websites.  

Memcached: Memcached is a high-performance, distributed memory object caching system that WordPress VIP uses for object caching. While it’s generic now, it can speed up dynamic web applications by alleviating database load.

LiteSpeed Cache: Specifically designed for websites hosted on LiteSpeed web servers, this plugin offers advanced caching features and optimization tools for WordPress sites.

KeyCDN: A content delivery network with caching services and global CDN coverage, real-time analytics, and HTTP/2 support for WordPress sites seeking performance optimization.

Common pitfalls to avoid

Caching validation

How do you tell when cached data should be considered invalid? Is it by age only? By the number of times it was used? When a certain kind of event triggers invalidation? When the data reaches a certain size? Cache invalidation has been called one of the thorniest questions in computer science

To avoid confusion, implement a robust cache invalidation strategy that integrates seamlessly with WordPress updates and content changes. You can find WordPress cache plugins and tools that offer granular cache control. This allows administrators to specify which content needs immediate invalidation upon updates.

You can also use cache purging techniques triggered by WordPress hooks or events. This ensures you get timely and efficient cache invalidation without compromising your site performance.

Inconsistent and incoherent caching

If your caching across different layers or edge servers is inconsistent it can lead to discrepancies in content delivery. That can mean unpredictable user experiences and potential content synchronization issues. To avoid this ensure your WordPress cache plugins and CDNs support cache synchronization. This will enable seamless propagation of updates across distributed cache layers.

You can also implement cache tagging or versioning that labels cached content and track dependencies. This will help keep your content delivery consistent across all cache nodes and reduce the risk of data going stale when the underlying data has changed, but the cached data has not been cleared.

Overhead management and storage concerns

When your cache accumulates large volumes of dynamic content, such  as results of database queries, media files, and dynamically generated pages, it can strain your server resources and consume significant storage space. It can even lead to what’s known as a cache stampede.

One way to avoid this challenge is to configure your cache expiration policies based on content volatility and user traffic patterns. This will lower your storage needs and reduce performance degradation. You can also use cache compression to reduce your data footprint and maximize storage efficiency without compromising retrieval speed.

Whatever you do, it’s a good idea to regularly monitor usage metrics and adjust your cache configurations regularly to maintain optimal performance and resource utilization. 

Maintaining security and reducing vulnerabilities

Often, what you cache will include potentially sensitive information. Storing user sessions, authentication tokens, or personal data, can all expose you to inadvertent risk or data leakage if not properly managed.

Additionally, if your caching mechanisms are misconfigured or inadequately secured they could inadvertently cache malicious content or expose cached resources to unauthorized access. That could mean security breaches or exploitation by malicious actors. Please deploy security measures, such as encryption, access controls, and secure cache policies, to ensure your cached materials don’t provide back-door access for bad actors. 

What are the benefits of caching?

As noted above, caching improves the performance of sites and applications. From a user’s perspective, that means: 

  • Faster page loads—Locally stored caching creates a smoother browsing experience.
  • Reduced server load—By serving cached content directly to users, caching eases server load and improves performance at scale.
  • Improved Scalability—With caching, websites can handle traffic spikes without experiencing performance degradation, ensuring a consistent user experience even during peak periods.
  • Improved and more stable application performance—Because caching enables faster memory transfer from either magnetic or SSD resources, sites run substantially faster and more reliably when they use it.
  • Bandwidth savings—Both the website owner and the user benefit from caching’s reduced data flow between the server and the client.

Real-world caching use cases

So how do all these considerations, resources, and solutions appear in practice? Let’s look at a few example use cases:

Ecommerce platforms

While you certainly don’t want to cache entire user sessions, (those would be better placed in a more secure Memcached or Redis resource), there are other uses for caching in ecommerce. For instance, you can improve user experiences by making things like viewed items faster and easier to serve up. 

Social media platforms

Repetition is one of the hallmarks of the social media world. When you can cache elements of a feed, returning and scrolling become more natural experiences. Profiles rarely change, as does media content that users return to again and again.

Content streaming services

When watching a video, it’s a much better experience when you can return to where you left off. Caching can provide this kind of refined experience and is an expected standard by modern users.

Enterprise applications

A huge and complex web presence can mean unnecessary difficulty in retrieving specific data from immense data sets. Caching can make the user experience on an intranet or internet much smoother by serving up data without making the user go back and search for it again and again.

Best practices and optimization techniques

To improve the functionality of your caching while saving deployment and management time, consider pre-built caching libraries or frameworks. These can be ready-made tools and APIs that help you facilitate the caching of data, resources, and computations. Consider using well-known solutions including Memcached and Redis as we discussed above.

To ensure ongoing cache performance remains high, you’ll want to monitor and analyze what’s going on in your caching solutions. You can find plugins for that as well at the WordPress plugin site.

As you consider which monitoring solutions you choose, look for those that offer detailed dashboards that can track hits, misses, and evictions over time. You’ll also want to implement alerting mechanisms for issues such as high cache miss rates or storage utilization exceeding predefined thresholds.

Remember to regularly analyze cache performance metrics and trends with periodic load testing and performance profiling. This will help you better understand how cache optimizations affect website responsiveness and scalability. 

Managing your website caching will always be a trade-off between caching benefits and resource utilization. You want enough data cached to create outstanding experiences, but you also need that data to be fresh so what’s served is most relevant and useful. That requires careful optimization of cache configurations, expiration policies, and storage allocation to mitigate performance degradation and storage costs. 

How WordPress VIP can help

Now that you know not only the caching basics, benefits, blockers, and best practices, you should be well prepared to take the next steps to improve the total experience of your enterprise web presence with WordPress VIP.

We can help you implement a site that delivers consistent, secure, and delightful user experiences that use the visitor’s history to its best advantage. Find out more about what WordPress VIP can do for you now.

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