Digital publishers’ guide to cache

What is cache?

During caching, copies of files or data are stored in a place where they can be accessed immediately. It can be compared to a warehouse that stores different types of digital files, such as scripts, images, and other data. There are two several types of cache you need to know (by the way, it’s pronounced /kæʃ/ – “kash”):

• Client-side caching – data is stored in the user’s local system. This type of cache falls into two additional categories:
  • browser caching (HTTP cache) – thanks to which a browser user, after revisiting a website, doesn’t have to load many of its elements again, like images or JavaScript files, CSS stylesheets, and HTML pages. After a non-expired resource is detected, the browser will automatically opt for it. What’s vital, users can clear HTTP cache data through browser settings,
  • service worker caching – although both HTTP cache and service worker caching are client-side systems, some distinctions are worth highlighting. With this kind of cache, resources are not utilized automatically because a developer needs to set some options so that requests won’t be served from the network but from the service worker’s cache. What’s more, this kind of cache is valuable when there is something wrong with the network (for instance, it’s unstable or down);
• Server-side caching – data is stored on the server. It’s mainly utilized to reduce server loads. The main purpose of it remains the same as in the two cases mentioned earlier – temporary storage of files and data, allowing for them to be reused later on. We can differentiate the following categories:
  • object caching, whose purpose is to store database queries,
  • opcode caching aims at storing precompiled script bytecode,
  • Content Delivery Network or CDN Caching – its objective is data storage in servers closer to the end users than the original server. One of the most popular ones is Cloudflare CDN, designed to suit WordPress users’ needs;
• Search engine cache – is an indexed (by a web crawler) version of a web page. When a user views a cached version of a web page, it’s often because it’s been altered, taken down, or some different problems occurred. Importantly, in 2024, Google opted to discontinue its web caching service, which was initially designed to assist websites temporarily offline or for users with slow internet connection. The company stated that the Internet has changed since the introduction of the service and encourages the use of the Wayback Machine, an Internet archive. This decision has raised concerns among SEO specialists who can no longer check their competitors’ alterations. Despite this, Bing and Baidu still offer similar features, but the importance of caching for SEO has for sure decreased after Google’s decision.

What is the difference between cookies and cache?

Although these two concepts are often associated, it should be noted that they are not the same. The cache saves data and files temporarily, so it’s possible to speed up the loading of pages. Cookies, on the other hand, are text files that store information about visits and choices of websites’ users, which include dates and times of each visit. What’s more, they are used to identify specific users and enhance their browsing experience. It’s worth noting that there is a trend to limit the use of third-party cookie files nowadays.

How Does Cache Work?

When it comes to server-side caching, the situation looks like this: after the user’s first visit to a certain webpage, data is taken from the server – as a result, the user sees the content. Later on, a webpage is copied and stored as a cache, so during a revisit, a cached copy of the page is displayed. Client-side caching looks similar, but data is retrieved from the user’s local system.