What potential memory usage concerns should be considered when using the readfile method in PHP for file downloads?

When using the readfile method in PHP for file downloads, potential memory usage concerns arise when dealing with large files. This is because the entire file is read into memory before being sent to the client, which can lead to high memory usage and potential performance issues. To mitigate this, it's recommended to use a combination of readfile and output buffering to stream the file to the client in smaller chunks, reducing memory usage.

$file = 'path/to/file.pdf';

// Set appropriate headers
header('Content-Description: File Transfer');
header('Content-Type: application/pdf');
header('Content-Disposition: attachment; filename="' . basename($file) . '"');
header('Content-Length: ' . filesize($file));
header('Cache-Control: private');
header('Pragma: private');
header('Expires: 0');

// Use readfile with output buffering to stream file in chunks
ob_clean();
flush();
readfile($file);