PHP Performance

OPcache

Production Configuration

; /etc/php/8.x/fpm/conf.d/10-opcache.ini
opcache.enable=1
opcache.memory_consumption=256          ; MB — increase for large codebases
opcache.interned_strings_buffer=16      ; MB — reduces string duplication
opcache.max_accelerated_files=20000     ; rounded to next prime internally
opcache.validate_timestamps=0           ; DISABLE in production — requires manual reset on deploy
opcache.save_comments=1                 ; required by Doctrine, PHPUnit, many frameworks
opcache.optimization_level=0x7FFEBFFF   ; all safe optimizations (default)

Development Configuration

opcache.enable=1
opcache.validate_timestamps=1           ; auto-detect file changes
opcache.revalidate_freq=0               ; check on every request

Key Directives

Preloading (PHP 7.4+)

opcache.preload=/var/www/app/preload.php
opcache.preload_user=www-data

// preload.php — loaded once at server startup
$directory = new RecursiveDirectoryIterator(__DIR__ . '/src');
$files = new RecursiveIteratorIterator($directory);
$php = new RegexIterator($files, '/\.php$/');
foreach ($php as $file) {
    opcache_compile_file($file->getRealPath());  // compiles without executing
}

JIT (PHP 8.0+)

opcache.jit=tracing             ; recommended mode (or "function" for simpler JIT)
opcache.jit_buffer_size=128M    ; 0 = JIT disabled

Monitoring & Management

// Check cache health
$status = opcache_get_status();
$hitRate = $status['opcache_statistics']['opcache_hit_rate'];  // target: >98%
$wasted = $status['memory_usage']['current_wasted_percentage'];
$full = $status['cache_full'];

// Reset cache (deploy hook)
opcache_reset();  // clears entire in-memory cache

// Invalidate single file
opcache_invalidate('/path/to/file.php', true);  // force=true ignores mtime

File Cache (Shared Hosting / CLI)

opcache.file_cache=/var/cache/opcache       ; persistent across restarts
opcache.file_cache_only=0                   ; 1 = skip shared memory entirely
opcache.file_cache_consistency_checks=1     ; validate checksums

Database (PDO)

// Recommended PDO configuration
$pdo = new PDO('mysql:host=localhost;dbname=app;charset=utf8mb4', $user, $pass, [
    PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,   // throw exceptions
    PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,         // assoc arrays
    PDO::ATTR_EMULATE_PREPARES   => false,                    // real prepared statements
]);

// Named parameters — clearer for multiple params
$stmt = $pdo->prepare('SELECT * FROM users WHERE email = :email AND active = :active');
$stmt->execute(['email' => $email, 'active' => 1]);
$user = $stmt->fetch();

// Transactions
$pdo->beginTransaction();
try {
    $pdo->prepare('UPDATE accounts SET balance = balance - ? WHERE id = ?')->execute([$amount, $from]);
    $pdo->prepare('UPDATE accounts SET balance = balance + ? WHERE id = ?')->execute([$amount, $to]);
    $pdo->commit();
} catch (\Throwable $e) {
    $pdo->rollBack();
    throw $e;
}

Caching (Redis / Memcached)

// Redis — cache-aside pattern
$redis = new Redis();
$redis->connect('127.0.0.1', 6379);

$key = 'user:' . $userId;
$cached = $redis->get($key);
if ($cached !== false) {
    return json_decode($cached, true);
}
$data = $db->fetchUser($userId);
$redis->setex($key, 3600, json_encode($data));  // TTL 1 hour
return $data;

// Memcached
$mc = new Memcached();
$mc->addServer('127.0.0.1', 11211);
$mc->set('key', $value, 3600);
$value = $mc->get('key');

SPL Data Structures

Micro-Optimizations

Function Choices — Prefer Faster Alternatives

Strings & Arrays

Memory Management

// Monitor memory usage
echo memory_get_usage(true);      // real OS allocation
echo memory_get_peak_usage(true); // max during script

// Free large variables explicitly
unset($largeArray);

// Force garbage collection in long-running processes
gc_collect_cycles();

Loops

// Cache count outside loop
$len = count($items);
for ($i = 0; $i < $len; $i++) { }

// foreach is idiomatic for arrays — use it
foreach ($items as $key => $value) { }

// Unset reference after foreach by-reference
foreach ($items as &$item) { $item = transform($item); }
unset($item);  // CRITICAL — prevents bugs from lingering reference

// array_map for simple transforms
$names = array_map(fn($u) => $u->name, $users);

Profiling