How to set up cache for php pages (three methods)

In web development, caching is an extremely important concept. It provides a way to solve performance problems and reduce the demand on server resources. PHP is a popular web language, and of course, it can also set up caching. This article will introduce how to set up caching in PHP pages.

1. What is cache

Cache is a very common term in the computer field. Its essence is to store frequently used data or programs close to users to improve access speed.

In web development, caching usually refers to storing a processed page or file in the memory of the web server to reduce the processing time for subsequent accesses.

2. Why use caching

In web development, page generation usually takes up a lot of time. When the number of visits increases, the load on the web server also increases. If each page request requires complete processing, the server's response time is likely to become very slow. Therefore, for those pages that are frequently requested, we can choose to cache these pages in memory, which can reduce the load on the Web server and improve the page response speed.

3. How to set up cache

In PHP, we can control browser cache and cache time by setting HTTP headers. The specific implementation method is as follows:

1. Set the page expiration time

If we know that the content of a page will not change soon, we can set its expiration time to a very long time. Long time to reduce server response time.

// 设置缓存时间为1小时
$expires = 3600;
header("Pragma: public");
header("Cache-Control: max-age=".$expires);
header('Expires: ' . gmdate('D, d M Y H:i:s', time() + $expires) . ' GMT');

In the above example, we set the cache time through Cache-Control. Here we set the cache time to 1 hour.

2. Set the page modification time

If we know that a page may be modified at a certain time, then we can set a Last-Modified tag to help the browser determine whether the page needs to be re-fetched. If the server modifies the page during future visits, the tag will be calculated at the same time.

// 读取文件修改时间并设置 Last-Modified 标记
$lastModifiedTime = filemtime($filePath);
$etag = md5_file($filePath);

header("Last-Modified: " . gmdate("D, d M Y H:i:s", $lastModifiedTime) . " GMT");
header("Etag: $etag");

In the above example, we used the filemtime() function to get the last modification time of the file, and the md5_file() function to get the Etag of the file value.

3. Set page content change tag

In order to alleviate browser cache problems, we can update a version number or other similar tags when the page content changes. And let the browser re-read the page. In this way, even if the page content has not changed, the browser can still obtain the new page, thereby avoiding the problem of expired pages.

// 增加版本号
$version = 1;
$url = "http://www.example.com/index.php?v=".$version;
header("Location: ".$url);

In the above example, we add a version number to the accessed URL and redirect the browser to the URL, so as to inform the browser to re-obtain the page when the page is updated.

4. Summary

In Web development, caching is a common method to improve page response speed. In PHP, we can control the cache and cache time of the page by setting HTTP headers. However, caching can also cause problems if not set up properly, such as causing some pages to never be updated. Therefore, when using cache, we need to pay special attention to the setting of the cache time and the regular update of the content change mark of the page.

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