How to Cache PHP Results
Although pages created using PHP offer a variety of compelling features not offered in standard HTML, generating PHP pages dynamically comes with a performance cost. Dynamically generating the text, images and other HTML elements that comprise a Web page often requires multiple server requests, even in situations where the Web page’s contents haven’t changed since the last time the page displayed. By caching PHP pages that do not change often, developers can take advantage of PHP’s dynamic features without requiring server requests for unchanging (static) page elements.
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Things You'll Need
- Text Editor
- PHP 4 or 5 installed on a Web server
- Read and write file and directory permissions on server
Instructions
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1
Open a text editor and create a new file. New files are typically created in text editors by selecting “New” from the “File” menu. Save the file as “php_cache.php” in a location on the Web server that has appropriate permissions.
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2
Add two PHP delimiters to the file (“<?php” and “?>”). The PHP interpreter will interpret any text placed between the two delimiters as code.
<?php
?> -
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3
Declare a PHP variable named “$fileCache”. Set the variable equal to the cache file’s name (the file that will hold the cached version of the page). Name the file “cache.html”.
$fileCache = "cache.html";
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4
Check for the existence of “cache.html” on the server. If a version of cache.html exists, include (load) cache.html from the server and exit php_cache.php.
if (file_exists($fileCache))
{
include($fileCache);
exit;
} -
5
Turn on output buffering using the “ob_start” PHP function. While buffering is on, any output from php_cache.php will be stored in a buffer.
ob_start();
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6
Use a PHP echo language construct to write an HTML header/title to the Web page. Because output buffering is on, this header will be written to the output buffer. To write the header, use an HTML “<h1>” tag, the text “Uncached Title” and close the “</h1>” tag.
echo "<h1>Uncached Title</h1>";
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7
Use a PHP “fopen” function to bind cache.html to an output stream. Open the file in write mode (“w”) and set the output stream to a variable named “$fileOpen”.
$fileOpen = fopen($fileCache, 'w');
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8
Use an “ob_get_contents” command to retrieve the contents of the output buffer. Use the PHP “fwrite” function to write the buffer’s contents to the $fileOpen output stream.
fwrite($fileOpen, ob_get_contents());
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9
Use the PHP “fclose” function to close the $fileOpen output stream once the output buffer has been written. Cache.html now contains the buffer’s contents, or the “Uncached Title” written using the echo command.
fclose($fileOpen);
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10
Use the “ob_end_flush” function to flush and close the output buffer. After adding the function, php_cache.html will appear as shown below.
<?php
$fileCache = "cache.html";
if (file_exists($fileCache))
{
include($fileCache);
exit;
}
ob_start();
echo "<h1>Uncached Title</h1>";
$fileOpen = fopen($fileCache, 'w');
fwrite($fileOpen, ob_get_contents());
fclose($fileOpen);
ob_end_flush();
?> -
11
Open php_cache.html in a Web browser. If this is the first time php_cache.html has been opened, the HTML “<h1>Uncached Title</h1>” will display using PHP. If php_cache.html has been opened previously, the HTML “<h1>Uncached Title</h1>” will be read from cache.html.
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Tips & Warnings
There are many ways to expire a cache. Some typical strategies include automatically deleting the cache file using a cron job, checking the cache file’s timestamp, and checking the cache file’s data.
To view caching in action, edit “cache.html” and change the header text to “Cached title”. Reload the page to verify that the data is pulled from the cache file.
Delete “cache.html” to force the PHP program to load the “<h1>” tag from the page’s PHP code.
Pages can be cached on the client using headers and Meta tags.
Caching should not be used on web pages that contain time sensitive information that expires often.
References
Resources
- Photo Credit Comstock/Comstock/Getty Images
