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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 by default caches the resolved file paths to avoid recalculating them every time, thus improving performance. realpath_cache_size is used to control the size of this cache.
When the file path resolution cache is full, PHP will clear the cache and recalculate the file path. If the file paths are called very frequently, appropriately increasing the cache size can reduce the frequency of cache clearing, thereby reducing file system operations and improving the overall performance of the application.
To configure realpath_cache_size, you can set it in PHP's php.ini configuration file. By default, the value of realpath_cache_size is 16KB, which is sufficient for most applications. However, in applications where file paths are resolved frequently, increasing the cache size can significantly improve performance.
To set realpath_cache_size in the php.ini file, for example:
realpath_cache_size = 64k
This will set the cache size to 64KB. If you need a larger cache, you can set it to a higher value, such as:
realpath_cache_size = 128k
If you're unsure about the current realpath_cache_size value, you can check it using the phpinfo() or ini_get() functions. For example:
<?php
echo ini_get('realpath_cache_size');
?>
This will return the current 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 validity time of the path data in the cache, in seconds. By default, the TTL is set to 120 seconds, meaning the cached path data will expire after 120 seconds.
You can adjust this parameter according to your needs. If your file paths do not change frequently, you can increase the TTL to allow the cached data to stay valid longer, reducing the frequency of cache clearing and recalculations:
realpath_cache_ttl = 3600
This will set the cache validity period to 3600 seconds (1 hour).
Increasing realpath_cache_size is not always the best choice. It is necessary only in the following cases:
High-Frequency File Path Resolution: If your application involves frequent file path resolutions (such as file system scans or numerous include and require calls), increasing the cache size can significantly improve performance.
Large Applications: For large projects that contain 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 times.
When increasing realpath_cache_size, ensure that the server has enough memory, as a larger cache will consume more memory.
In extreme cases, a cache that is too large may lead to high PHP memory usage, so adjustments should be made based on actual needs.
Frequent cache clearing may lead to performance issues, so try to balance cache size and TTL settings according to the application’s requirements.
