Imagine you are in a library. You have all of your favorite books right next to you. This means you don't need to rush to the bookshelf every time you want to read one of your books of choice. A similar concept is applied in computer technology by trying to keep frequently accessed data close at hand.
In this topic, you will learn about caching, its types, and the impact caching has on modern computing. You will also look at how caching works as well as ascertain its pros and cons.
Caching and its importance
Caching in its simplest form, is the process of temporarily storing data to improve responsiveness. This data could be anything from web pages to images, API responses, or even chunks of pre-computed data. The primary objective of caching is to make websites more responsive by reducing the load on backend resources.
Let's take an example of a web application that loads with images, CSS, and JavaScript files already cached in the user's browser. Users will experience an instant and seamless browsing experience. Or a content-heavy website that maintains servers in different locations to cache and distribute data across multiple locations worldwide. This method allows content access from a server closest to the user location, which in turn reduces latency and network congestion. The use of caching greatly improves data availability with quick response time.
Caching is a fundamental building block that empowers the seamless functioning of web applications. It reduces the burden on backend servers, enhances user experience, and contributes to more sustainable and scalable application architecture. Let's look at the different types of caching starting with client-side caching.
Client-side caching
When a user visits a web page, your computer's local storage can store static resources like images, stylesheets, and scripts. By doing so, subsequent visits to the same website are much faster, as resources are locally accessible. You don't have to download them all over again. This is known as client-side caching as the client's computer stores necessary resources instead of the server.
This mechanism substantially reduces load times for return visitors as the cached resources are readily available. Client-side caching not only benefits users but also eases the load on servers. Servers have an easy time as they receive fewer requests for static resources. An example of client-side caching is the caching that your browser does to save certain parts of the website. So that next time you visit the same website, the browser loads data from the cache instead of requesting the server.
Now that you've looked at how caching can be done on the client side, what about caching data in the server itself?
Server-side caching
Let's suppose you visit a website. The website prompts certain information that you provide and processes it to give a web page with personalized data. This process occurs the first time you visit a website. However, you may visit the website again after some time, or someone else may send the same request to the server as you did. To avoid spending precious processing and database resources for the same processes, the server stores a copy of the response in the server itself. So, the next time you visit the site or someone sends the same request, the server can send the cached data instead of regenerating a new response.
This process is known as server-side caching and is especially effective for data that remains relatively stable and doesn't change frequently. When someone requests pre-cached data, the server can effortlessly retrieve it. Hence, we avoid time-consuming trips to disk storage or remote servers.
We've talked about storing data as a cache either with the client or the server for frequent access. But sometimes, the major bottleneck that reduces responsiveness is the distance between the client and the server. To combat this, let's take a look at intermediate caching.
Intermediate caching
When communication traffic between servers and their clients has to move over large physical distances, we experience latency issues or delays in communications. For example, popular websites like YouTube or Facebook host content that is shared all across the globe. To reduce latency, they employ various CDNs that sit between the client and the server.
Content Delivery Networks (CDNs) employ caching at a global scale to optimize content distribution and store static website content on multiple servers in the network. CDNs consist of a network of multiple servers spread all across the world. The use of a CDN significantly reduces latency and network congestion by allowing users to access content from a nearby server rather than a distant origin server. This caching strategy enhances user experience, especially for users located far away from the original data source.
As the CDN handles content delivery, it reduces the load on the origin server. The end result is improved performance and global scalability for websites and applications with a broad user base.
Now that you know about the different types of caching, let's take a peek at how it works.
Overview of the caching process
Caching might seem like magic, but it's actually a well-orchestrated process. Here's a simplified overview:
When an application needs data, it first checks the cache to determine if the required data is already available. This process is known as a cache lookup. We avoid having to spend costly trips to data sources. During the cache lookup process, there are two possible outcomes: a "cache hit" or a "cache miss."
If the data is found in the cache then a cache hit occurs. The application can swiftly fetch the data and won't spend considerably more time searching elsewhere. However, if the data isn't in the cache a cache miss occurs. The application now needs to retrieve it from the source which may be a database, remote server, or some other external source. After fetching the data, it needs to be stored in the cache for future use to increase the chances of cache hit next time the same data is requested.
To maintain data accuracy and freshness, cache memory implements an expiration mechanism called cache expiration. Cached data has a limited lifespan, after which it is considered stale and needs to be refreshed. When the data reaches its expiration time, it is removed from the cache. Any applications requiring the same data will fetch a fresh copy from the original source ensuring that the cache only contains up-to-date and relevant data. Cache expiration is critical for ensuring that users receive the latest information from dynamic applications and that cached data remains synchronized with the data in the backend systems.
Advantages and downsides of caching
As you already know, caching's primary purpose is to improve the response time of web servers. In trying to improve response times, we employ caching on client, server, or CDNs that also reduce load on the server as fewer requests are sent to the server and pre-processed data can be sent as a response. Reduced server load means that the server doesn't have to work as hard. This reduces the cost of server operation as well.
By caching data and offloading requests from backend servers, applications can scale more effectively to accommodate a growing number of users and handle sudden spikes in traffic without impacting performance. Caching also provides an added layer of redundancy where cached data can act as a collection of frequently accessed entries. This allows the service to keep functioning even if the full copy of data is not accessible at the moment.
However, the story isn't all sunshine and rainbows. While caching offers numerous advantages, it also comes with some potential drawbacks:
- Cache invalidation complexity: Managing cache expiration and ensuring that cached data remains up-to-date is very difficult, especially in dynamic applications where data changes frequently. Cache invalidation mechanisms need to be carefully implemented to avoid serving stale or outdated data to users.
- Data consistency: Caching can introduce data consistency issues, particularly in distributed systems. When using multiple cache instances, it becomes complex to ensure data consistency across caches. Maintaining consistency between cached data and the backend is absolutely necessary for cache implementation.
- Cache hotspots: In some cases, certain data or resources might be disproportionately accessed. Such a case leads to cache hotspots. When multiple users or processes compete for the same cached item, it can result in an uneven load on cache servers. Some cache servers receive much more traffic than others. This can lead to increased response time and errors related to resource contention.
- Cache poisoning and security risks: Cache poisoning is a security concern where an attacker manipulates cached data to inject malicious content. Proper cache security measures like data validation and sanitization are essential to mitigate such risks.
Conclusion
Despite its challenges, caching is a crucial part of modern computing, powering everything from web browsing to video streaming and even online gaming. Understanding caching can help you build faster, more efficient applications, and provide a better user experience. In this topic, we discussed the following points:
- Caching is the process of temporarily storing data to improve responsiveness.
- Client-side caching — the client stores static content of webpages and websites in their own storage resource to reduce load time for subsequent visits.
- Server-side caching — the server stores data temporarily for reusing which reduces the need to process requests and access the database.
- CDN caching — intermediate caching where servers close to the user store content to reduce access times for users that are located far away from the original server.
- The process of caching includes cache lookup, cache hit, cache miss, and cache expiration.
- Caching has many upsides like improved response times, reduced load on servers, and cost savings among others. However, its downsides must also be taken into careful consideration.