What are the potential risks of sending multiple parallel requests to a server using PHP for web scraping purposes?

Sending multiple parallel requests to a server using PHP for web scraping purposes can overload the server, leading to performance issues or even causing the server to block your IP address. To avoid this, you can limit the number of parallel requests using techniques like asynchronous processing or using a queue system to control the rate of requests sent to the server.

// Example code snippet using GuzzleHttp to limit the number of parallel requests
use GuzzleHttp\Client;
use GuzzleHttp\Promise;

$client = new Client();
$promises = [];

// Limit the number of parallel requests to 5
foreach ($urls as $url) {
    $promises[] = $client->getAsync($url);
    
    if (count($promises) >= 5) {
        Promise\settle($promises)->wait();
        $promises = [];
    }
}

Promise\settle($promises)->wait();