Master common caching mechanisms to improve HTTP caching efficiency

Efficiently utilize HTTP caching: What are the commonly used caching mechanisms?

Introduction:
In network applications, in order to improve user experience and reduce network resource consumption, caching technology is a very important component. HTTP caching mechanism is one of the commonly used caching technologies. By saving a copy of resources between the client and the server, it can effectively reduce the number of network requests and the amount of data transmitted. This article will introduce commonly used HTTP caching mechanisms. Mastering these mechanisms can help us make efficient use of cache and improve website performance.

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1. Forced caching
   Forced caching is achieved by setting the Expires and Cache-Control fields in the HTTP response header. When the client receives the response to the first request, it will cache the resource. When requesting the resource again in the future, it will first check whether it has expired. If it has not expired, it will read it directly from the cache without requesting the server again. Expires is an absolute timestamp indicating the expiration time of the resource. Cache-Control is a more flexible field that can specify the maximum storage time of resources (max-age), whether to allow caching (public/private), whether to allow proxy caching (s-maxage), and whether to force revalidation (must -revalidate) etc. Forced caching is an efficient and fast caching mechanism that can greatly reduce the number of network requests.
2. Comparison cache
   Comparison cache is used when the cache is forced to expire. When the client initiates a request, the server will add an ETag field or Last-Modified field to the response header, which represents the unique identifier and last modified time of the resource respectively. The next time the client requests the resource, it will add these fields to the request header through the If-None-Match and If-Modified-Since fields and send it to the server. The server determines whether the resource needs to be resent by comparing the values ​​of these fields with the current resource information. If the resource has not changed, the server returns a 304 status code and tells the client that the resource can be obtained from the cache. Otherwise, the server will return the new resource.
3. Cache validity verification
   Cache validity verification is a supplement to the contrast caching mechanism. It uses the value of the Cache-Control field in the HTTP header. If its value is no-cache or no-store, it means that the resource cannot be cached or the cache copy is not allowed to be used. The client must initiate a request to the server and retry it. Access to resources. In addition, you can also disable caching by adding the Pragma field in the request header and setting its value to no-cache.
4. Hybrid caching (CDN cache)
   Hybrid caching refers to deploying static resources on the CDN (content distribution network) of multiple nodes, allowing the browser to obtain resources from the node closest to it. The CDN node will add the Expires and Cache-Control fields in the response header of the static resource so that the resource can be cached by the client. At the same time, CDN nodes will also use cache synchronization technology to achieve resource consistency, ensuring that users can obtain the latest resources anywhere. Hybrid caching technology can reduce server load and improve user access speed and experience.

Conclusion:
HTTP caching mechanism is an important means of network performance optimization. By rationally using the caching mechanism, the number of network requests can be greatly reduced, the load on the server can be reduced, and the response speed of the website and the user experience can be improved. In practical applications, we need to select appropriate caching mechanisms to improve website performance based on different business scenarios and needs, and combine caching strategies and technologies for tuning and maintenance. Only by deeply understanding and mastering commonly used caching mechanisms can we maximize the benefits of caching technology in practice.

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