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In PHP, the realpath() function is used to resolve a given file path and return its absolute path. When realpath() is called multiple times, PHP will cache the resolved file paths by default to avoid repeating calculations and thus improve performance. realpath_cache_size controls the size of this cache.
When the file path resolution cache is filled, PHP will clear the cache and recalculate the file paths. If file paths are frequently accessed, increasing the cache size appropriately can reduce the frequency of cache clearance, which in turn reduces the number of file system operations, improving the overall performance of the application.
To configure realpath_cache_size, you can set it in the PHP php.ini configuration file. By default, the value of realpath_cache_size is 16KB, which is sufficient for most applications. However, in some applications where file paths are frequently resolved, increasing the cache size can significantly improve performance.
To set realpath_cache_size in the php.ini file, for example:
<span><span><span class="hljs-attr">realpath_cache_size</span></span><span> = </span><span><span class="hljs-number">64</span></span><span>k</span>This will set the cache size to 64KB. If you need a larger cache, you can set it to a higher value, such as:
<span><span><span class="hljs-attr">realpath_cache_size</span></span><span> = </span><span><span class="hljs-number">128</span></span><span>k</span>If you're unsure of the current realpath_cache_size value, you can check it using the phpinfo() or ini_get() function. For example:
<span><span><span class="hljs-meta"><?php</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">ini_get</span></span><span>(</span><span><span class="hljs-string">'realpath_cache_size'</span></span><span>);
</span><span><span class="hljs-meta">?></span></span><span>
</span></span>This will return the currently configured cache size.
In addition to realpath_cache_size, realpath_cache_ttl is another important configuration related to file path caching. realpath_cache_ttl defines the time-to-live (TTL) of cached path data in seconds. By default, TTL is 120 seconds, meaning that cached path data will expire after 120 seconds.
You can adjust this parameter as needed. If your file paths do not change frequently, you can increase the TTL value to allow cached data to persist for a longer period, thus reducing cache clearance and recalculation frequency:
<span><span><span class="hljs-attr">realpath_cache_ttl</span></span><span> = </span><span><span class="hljs-number">3600</span></span><span>
</span></span>This will set the path cache's TTL to 3600 seconds (i.e., 1 hour).
Increasing realpath_cache_size is not always the best choice, and it is necessary only in the following situations:
Frequent File Path Resolution: If your application involves a large amount of file path resolution (such as file system scanning, frequent include and require calls, etc.), increasing the cache size can significantly improve performance.
Large Applications: For large projects with many files or directories, properly configuring realpath_cache_size can reduce the overhead of file path resolution.
High Load Environments: In high-load production environments, increasing realpath_cache_size can reduce file system access and improve response speed.
When increasing realpath_cache_size, ensure that the server has enough memory, as a larger cache will consume more memory.
In extreme cases, an overly large cache might lead to excessive PHP memory usage, so adjustments should be made based on the actual situation.
Frequent cache clearance might cause performance issues, so try to balance cache size and TTL settings based on your application's needs.
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