Object Pooling

Also Known As

TL;DR

Explanation

Object pooling maintains a pool of reusable objects (database connections, HTTP clients, worker threads) that are checked out, used, and returned rather than instantiated fresh each time. In traditional PHP request-per-process model, object pools within a single request have limited value — the process dies anyway. They become highly relevant in long-running PHP contexts: Swoole coroutines, RoadRunner workers, or CLI queue workers that handle many tasks. Database connection pools (pgBouncer, ProxySQL) operate at the infrastructure level and benefit all PHP architectures. In-process pools in PHP-FPM should be evaluated carefully — memory is not shared between workers.

Common Misconception

Why It Matters

Common Mistakes

• Not resetting object state before returning to pool — a 'dirty' object from one request affects the next.
• Pool size not matched to concurrency — too small causes wait queues; too large wastes memory.
• Pooling cheap objects — the pool management overhead exceeds the construction savings for simple objects.
• Not handling exceptions that leave an object in an invalid state — the broken object must not return to the pool.

Code Examples

// Creating a new HTTP client on every request — expensive:
function callApi(string $url): array {
    $client = new GuzzleHttp\Client(['timeout' => 5]); // New client each call
    return $client->get($url)->json();
    // Guzzle clients are reusable — inject a shared instance instead
}

// Reuse expensive objects rather than constructing and destroying repeatedly
class PdfRendererPool {
    private \SplStack $pool;

    public function __construct(private int $size = 4) {
        $this->pool = new \SplStack();
        for ($i = 0; $i < $size; $i++) {
            $this->pool->push(new PdfRenderer()); // pre-warm
        }
    }

    public function acquire(): PdfRenderer {
        return $this->pool->isEmpty()
            ? new PdfRenderer()  // overflow — create temporary
            : $this->pool->pop();
    }

    public function release(PdfRenderer $r): void {
        if ($this->pool->count() < $this->size) {
            $this->pool->push($r); // return to pool
        }
        // else let it GC — pool is full
    }
}

References

• ↗ https://en.wikipedia.org/wiki/Object_pool_pattern

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