Research on HTTP caching mechanism: What are the commonly used caching strategies?

In-depth understanding of HTTP caching mechanism: What are the common caching strategies?

Introduction:
With the rapid development of the Internet, web page loading speed has become one of the important indicators of user experience. In order to optimize the loading speed of web pages and reduce bandwidth consumption and server pressure, the HTTP caching mechanism has become an indispensable part. In Internet technology, caching is a technology that temporarily stores data in temporary storage to improve access speed. This article will delve into the principles of the HTTP caching mechanism and introduce common caching strategies.

1. Principle of HTTP caching mechanism:
The HTTP caching mechanism is based on the agreement between the client and the server and improves performance by storing and reusing previously obtained resources. When the browser sends a request to the server, the server will return the corresponding resources, such as HTML, CSS, JavaScript, images, etc. These resources can be cached by the browser so that they can be reused on subsequent requests. When the browser requests the same resource again, it first checks the cache. If the resource has been cached and has not expired, the browser will fetch the resource directly from the cache without having to make another request to the server, thus increasing loading speed.

2. Common caching strategies:

1. Forced caching:
   Forced caching strategies control the cache validity period by setting the Expires or Cache-Control field in the response header. If the resource is within the validity period, the browser will load the resource directly from the cache. Commonly used Cache-Control field values ​​include max-age and s-maxage. For example, setting max-age=86400 means that the resource is valid for 86400 seconds. If the resource has expired, the browser will initiate a request to the server to check whether the resource has been updated.
2. Comparison cache:
   The comparison cache strategy determines whether the resource has been updated by comparing it with the server. The server sets the Last-Modified or ETag field in the response header, which represents the last modification time of the resource and the unique identifier of the resource respectively. When the browser requests the resource again, the If-Modified-Since or If-None-Match field is added to the request header for comparison with the server. If the resource has not changed, the server will return a 304 Not Modified status code to tell the browser to use the cache directly. Otherwise, the server will return the latest resource.
3. Manual refresh:
   Manual refresh strategy means that the user actively clicks the browser's refresh button to force the browser to re-request and load the latest resources. This strategy is suitable for situations where users need to update resources in a timely manner, such as news websites, social media, etc.
4. CDN cache:
   CDN cache is a distributed caching solution that speeds up the loading of resources by storing static resources on CDN nodes closer to users. CDN caching is generally used in conjunction with forced caching and comparison caching to improve page loading speed, save server bandwidth, and improve user access experience.
5. Dynamic caching:
   Dynamic caching refers to a strategy that dynamically generates and caches responses based on specific parameters of the request. This policy applies to dynamically generated content, such as pages or data dynamically generated based on user login status, geographical location, etc.

Conclusion:
HTTP caching mechanism plays an important role in improving web page loading speed, reducing network traffic and server pressure. Common caching strategies include forced caching, comparison caching, manual refresh, CDN caching, dynamic caching, etc. Developers can reasonably select and configure caching strategies according to specific application scenarios, thereby improving user access experience.

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