Think of the last time you had to stop at a store and buy some food for dinner. You may have had to wait in line or maybe had to search for what you needed on the shelves. However, if you arrived just as someone was leaving with their purchase, then you might be able to find everything more quickly and simply than before. This is an example of caching: making things more available by keeping them somewhere easy to access later.
The cache is also another name for a persistent data structure that stores recently accessed data. So. future requests can reference the cached version instead of repeating complicated procedures such as database calls.
Since its introduction to computing, the concept has been carried over through many different fields when seeking ways to ease the strain on databases. A cache is a valuable tool that can help access requested data more quickly for a better user experience. And has been used in many different ways to improve websites.
How Does a Cache Work?
A cache is a storage area that holds data so future requests for that data can be served faster. A typical cache will hold the most recently accessed items, allowing them to be accessed more quickly by a computer system if needed again.
A cache stores copies of items from another collection called the source. To determine if an item should be cached or not, a cache requires an algorithm for deciding whether or not it should store an item or serve it directly from the source collection.
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Types Of Cache
Traditionally, there are five types of caches:
While all caches serve the same primary purpose – to reduce latency between requests for cached data, each type of cache has its own unique characteristics that make it better suited for one purpose than another. Here is how each type of cache works and scenarios where it would be used.
1. CPU Cache (Central Processing Unit)
The CPU cache memory is a small amount of memory dedicated to caching the relatively slow speed of the computer’s main memory (RAM). Data is moved from RAM to cache when referenced multiple times in anticipation of another reference to that data.
- The CPU monitors what data in RAM has been used recently and anticipates what information might be needed in future calculations.
- When a process requests data not in the disk cache, it can take much longer than usual because accesses are only made to read this slowed-down data.
- CPUs manage their caches automatically, so there usually isn’t any user input required for when an object should be cached or not.
2. Web Cache (or HTTP Cache)
A web browser cache is temporary storage for recently requested and already retrieved data. As it is directly connected to the network, Web Cache saves bandwidth because requests from clients can be served from the cache if the objects are still valid.
- In other words, only new or changed objects that have not been cached would require a server request instead of using an object that has already been downloaded from the original source.
- This process significantly decreases latency by reducing round-trips between client and web application servers.
- Web caches operate at lower levels in the OSI model than other caches do. Caching occurs on an L4 protocol such as TCP or UDP, whereas traditional disk caches occur below the L1 level.
- A web cache must be easily identified so that it can forward appropriate requests to it. This is accomplished through a special header that can be added to HTTP responses by web browsers.
- The value of this header is often the same as the filename of the currently cached object, which allows for easy identification if another request comes in for this object.
3. Database Cache
A database cache stores data and recently referenced objects in RAM, allowing faster access than reading from disk storage. Database objects such as tables and indexes are stored in secondary storage such as hard disks. They must be managed and queried from disk, which is significantly slower than RAM. Database caches serve the same purpose as web caches: to reduce latency between requests for cached data.
- Caches can often also increase throughput when there are many reads. But few write to a database because less data needs to be read from secondary storage.
- Caching in the database increases the likelihood that objects requested will already reside in memory. Hence, reducing wait times and improving performance.
- This caching benefits individual users and content delivery networks who want efficient access to static resources such as images, CSS files, or HTML pages.
4. Content Delivery Network (CDN) Cache
The job of a content delivery network is to serve the static content as close as possible to where it will be used or consumed. CDNs can then deliver this cached content at a much higher speed and with lower latency than if the request was sent back to the origin server. It could be located across from the continent from the user, especially if it’s a high-traffic website.
For this reason, CDNs are often employed by websites that receive large amounts of traffic. Such as Google, Facebook, or Amazon. In addition, popular sites might prefer using their CDN rather than paying another company for its users. It is to save money while further improving performance. In some cases, the users might need to remove memory cache or browser cache temporary files to access data more easily.
5. Domain Name (DNS) Cache
The domain name system (DNS) is the service that translates a URL, such as “example.com” to its corresponding IP address. DNS requests are usually cached because they don’t change often and therefore need not be done frequently. The caching of DNS lookups is critical for improving performance on the Internet.
Without caching, every lookup would require one request per cache miss, severely reducing the effective bandwidth due to latency issues.
Why Should You Clear Your Cache?
Now that you know what types of caches exist, you should also want to clear your cache. Why?
Problems may arise when cached data is out-of-date because it reflects the state of files at a previous point in time rather than how they are currently stored on a disk. When this happens, users will be presented with old data, leading to anything from minor annoyances to major problems. In this case, clear browsing data stored by CPU or other cached images is essential.
Summing Up
Since computing was introduced into society’s everyday life, there has been ongoing development of different ways to access and store data more effectively for both speed and ease of use. Cache memory is of prime importance in this regard and must be used effectively.
Maryam has been teaching IT as a school teacher for over a decade, and her main subject of choice is Internet safety, especially helping parents keep their families safe and secure online. When Maryam is not teaching or writing she is a big fan of the outdoors, the complete opposite of staring at a computer screen for hours.
