Reusing the same curl handle. Big performance increase?

Question

Crossposted from Should I close cURL or not? because I think it’s relevant here too.

I tried benching curl with using a new handle for each request and using the same handle with the following code:

ob_start(); //Trying to avoid setting as many curl options as possible
$start_time = microtime(true);
for ($i = 0; $i < 100; ++$i) {
    $rand = rand();
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, "http://www.google.com/?rand=" . $rand);
    curl_exec($ch);
    curl_close($ch);
}
$end_time = microtime(true);
ob_end_clean();
echo 'Curl without handle reuse: ' . ($end_time - $start_time) . '<br>';

ob_start(); //Trying to avoid setting as many curl options as possible
$start_time = microtime(true);
$ch = curl_init();
for ($i = 0; $i < 100; ++$i) {
    $rand = rand();
    curl_setopt($ch, CURLOPT_URL, "http://www.google.com/?rand=" . $rand);
    curl_exec($ch);
}
curl_close($ch);
$end_time = microtime(true);
ob_end_clean();
echo 'Curl with handle reuse: ' . ($end_time - $start_time) . '<br>';

and got the following results:

Curl without handle reuse: 8.5690529346466
Curl with handle reuse: 5.3703031539917

So reusing the same handle actually provides a substantial performance increase when connecting to the same server multiple times. I tried connecting to different servers:

$url_arr = array(
    'http://www.google.com/',
    'http://www.bing.com/',
    'http://www.yahoo.com/',
    'http://www.slashdot.org/',
    'http://www.stackoverflow.com/',
    'http://github.com/',
    'http://www.harvard.edu/',
    'http://www.gamefaqs.com/',
    'http://www.mangaupdates.com/',
    'http://www.cnn.com/'
);
ob_start(); //Trying to avoid setting as many curl options as possible
$start_time = microtime(true);
foreach ($url_arr as $url) {
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_exec($ch);
    curl_close($ch);
}
$end_time = microtime(true);
ob_end_clean();
echo 'Curl without handle reuse: ' . ($end_time - $start_time) . '<br>';

ob_start(); //Trying to avoid setting as many curl options as possible
$start_time = microtime(true);
$ch = curl_init();
foreach ($url_arr as $url) {
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_exec($ch);
}
curl_close($ch);
$end_time = microtime(true);
ob_end_clean();
echo 'Curl with handle reuse: ' . ($end_time - $start_time) . '<br>';

And got the following result:

Curl without handle reuse: 3.7672290802002
Curl with handle reuse: 3.0146431922913

Still quite a substantial performance increase.

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