Benchmarking listing files in a local directory in PHP

Yesterday, I ran the benchmark no one was waiting for: all the different ways to list files in a local directory in PHP.

The methods I benchmarked were scandir, readdir, glob and DirectoryIterator.

Unsurprisingly, the runtime grows linearly with the number of directory entries.

A lot of time is spent on sorting, scandir("", SCANDIR_SORT_NONE) and glob("*", GLOB_NOSORT") are both at least 10-30% faster than their sorted versions (which is the default).

scandir("", SCANDIR_SORT_NONE) is consistently the fastest option, with readdir coming in second.

Interestingly, DirectoryIterator is the slowest option for directories with less than 2000 files, but then its relative performance increases until it is about as fast as readdir and scandir for directories with 10000 files.

You can view the raw results or the benchmarking code I used below. Times are in ms and taken as the average across 100 iterations.

Benchmark results

files	DirectoryIterator	readdir	scandir	scandir unsorted	glob	glob unsorted
1	0.008	0.006	0.006	0.006	0.006	0.005
10	0.013	0.009	0.009	0.008	0.010	0.009
100	0.071	0.041	0.046	0.039	0.056	0.049
1000	0.683	0.376	0.477	0.357	0.568	0.449
10000	3.994	3.872	5.248	3.612	6.277	4.472

Benchmark code

<?php

namespace D;

class DirectoryReader
{
    public function __construct(
        protected string $directory,
    ) {
    }

    public function iterator($flags = 0)
    {
        $results = array();
        foreach (new \DirectoryIterator($this->directory) as $fileInfo) {
            $results[] = $fileInfo;
        }
        return $results;
    }

    public function readdir($flags = 0)
    {
        $results = array();
        if ($handle = opendir($this->directory)) {
            while (false !== ($filename = readdir($handle))) {
                $results[] = $filename;
            }
            closedir($handle);
        }
        return $results;
    }

    public function scandir($flags = 0)
    {
        return scandir($this->directory, $flags);
    }

    public function glob($flags = 0)
    {
        return glob($this->directory . '/*', $flags);
    }
}

if (empty($argv[1])) {
    echo "Usage: php " . basename(__FILE__) . " <directory>\n";
    exit(1);
}

$directory = $argv[1];
if (is_dir($directory)) {
    echo "Directory exists already\n";
    exit(1);
}

mkdir($directory, 0755);

$reader = new DirectoryReader($directory);
$n_iterations = 100;
$step_size = 10;
$tests = [
    ['iterator', 0],
    ['readdir', 0],
    ['scandir', 0],
    ['scandir', SCANDIR_SORT_NONE],
    ['glob', 0],
    ['glob', GLOB_NOSORT],
];

echo "files\t" . join("\t", array_map(function ($t) {
    $name = $t[0];
    if ($t[1]) {
        $name .= ' unsorted';
    }
    return $name;
}, $tests)) . "\n";


for ($n = 1; $n <= 10000; $n *= 10) {
    for ($f = (int) ($n / 10); $f <= $n; $f++) {
        touch("{$directory}/{$f}.txt");
    }

    $line = "{$n}\t";
    foreach ($tests as [$method, $flags]) {
        $start = microtime(true);
        for ($i = 0; $i < $n_iterations; $i++) {
            $reader->{$method}($flags);
        }
        $end = microtime(true);
        $time_per_it = sprintf('%.3f', ($end - $start) / $n_iterations * 1000);
        $line .= "$time_per_it\t";
    }
    $line .= "\n";
    echo $line;
}