Explore the secrets of HTTP caching: master the understanding of various caching strategies

In-depth analysis of the HTTP caching mechanism: What are the different caching strategies?

Introduction:
In the era of the Internet, network performance often becomes one of the key factors in user experience, and the HTTP caching mechanism, as an optimization method, can improve the loading speed of web pages and reduce the load on the server. Improve user experience. This article will provide an in-depth analysis of the HTTP caching mechanism and introduce common caching strategies.

1. The basic principle of HTTP caching mechanism
The basic principle of HTTP caching mechanism is to save the requested resources in the cache. When the same resources are requested again, they are obtained directly from the cache instead of re-requesting the server. ask. This reduces network latency and bandwidth consumption and improves performance.

2. HTTP caching strategy

1. Forced caching
   Forced caching means that when the client requests a resource for the first time, the response header returned by the server contains cache-related information. field, the client will cache the resource locally after receiving the response. When requesting the resource again, it will be obtained directly from the cache. During the cache validity period, the client will not send a request to the server, reducing bandwidth usage and delay. Common cache fields are: Expires and Cache-Control.
2. Negotiate Caching
   When the cached resource expires or is not forced to be cached, the client will send a request with a cache verification field to the server, and the server will verify whether the resource has changed based on this field. If the resource has not changed, the server returns 304 Not Modified and the client obtains the resource from the cache. If the resource changes, the server returns the new resource and the corresponding cache-related fields. Common cache verification fields are: Last-Modified and ETag.
3. Offline caching
   Offline caching refers to saving the resources of the web page on the client by using the manifest file, so that users can continue to access the web page when the network is unavailable. When the user connects to the network again, the browser will check whether the manifest file has changed, and if there is no change, the resource will be obtained directly from the cache. Offline caching can be achieved through HTML5 Application Cache.
4. Shard caching
   Shard caching refers to dividing resources into multiple small blocks and caching only the required resources, thereby reducing bandwidth consumption. Common shard caching methods include: paged loading, on-demand loading, lazy loading, etc.
5. CDN Cache
   CDN (Content Delivery Network) caching refers to caching the static resources of the website on distributed server nodes, which reduces the distance and delay of network transmission and improves the loading speed of resources. CDN caching is often used to accelerate static resources such as images and videos.
6. Front-end browser caching
   Front-end browser caching refers to caching static resources in the user's browser. The next time the same web page is accessed, the resources are obtained directly from the browser's cache. Browser caching can be controlled by setting the Expires and Cache-Control fields in the HTTP response header.

Conclusion:
HTTP caching mechanism is an important means to improve web page performance. Proper use of caching strategies can effectively reduce bandwidth consumption and delay, and improve user experience. This article introduces the basic principles of the HTTP caching mechanism and details common caching strategies. I hope readers can deepen their understanding of the HTTP caching mechanism through this article and apply it reasonably in actual development.

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