Excessive File I/O

Also Known As

TL;DR

Explanation

File I/O is orders of magnitude slower than memory access. Reading a file once per request is fine; reading the same file inside a loop that runs 100 times per request multiplies the I/O cost 100×. The standard fix is a static cache: static $cache = []; if (!isset($cache[$key])) { $cache[$key] = file_get_contents($path); } return $cache[$key]; The first read hits disk; subsequent reads return the cached value instantly.

Common Misconception

Why It Matters

Common Mistakes

• Reading configuration files on every request instead of loading once at startup.
• Not caching file_get_contents() results for files that rarely change.
• Writing to log files synchronously on every request — use async logging or a buffer.
• Checking file_exists() in loops — each call is a filesystem syscall.

Code Examples

// Reading the same file on every request inside a loop
foreach ($userIds as $id) {
    $config = file_get_contents('/etc/app/config.json'); // disk hit every iteration
    $cfg    = json_decode($config, true);
    process($id, $cfg);
}

// Read once, reuse in memory
$cfg = json_decode(file_get_contents('/etc/app/config.json'), true);
foreach ($userIds as $id) {
    process($id, $cfg);
}

// For cross-request reuse: OPcache can cache PHP arrays returned from files
// config/cache.php → return [...]; and use opcache_invalidate() on change

References

• ↗ https://www.php.net/manual/en/function.file-get-contents.php
• ↗ https://www.php.net/manual/en/function.opcache-get-status.php

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