Host this php on php-fpm + nginx, each page hit creates TWO Pairs of connections to replicaset, FOUR Authentication done (primary + secondary) * 2

gistfile1.php

<?
// simple mongoclient dumpper
$a=getMongo();
$b=getMongo();

var_dump($a->getConnectionss());
print("===================================SECOND MONGO CONN REQUEST ===================================\n");
var_dump($b->getConnectionss());

function getMongo(){//{{{
            $mongo  = new MongoClient(MG_HOST, array(
                    'replicaSet' => MG_REPLICASET,
                    'password'=>MG_PWD,
                    'username'=>MG_USER,
                    'db'=>MG_DB,
                    'journal' => true,
                    "readPreference"=> MongoClient::RP_SECONDARY_PREFERRED
                )
            );

            $mgdb = $mongo->{MG_DB};
        return $mongo;
}
?>

Take a look at mongo_connection_ismaster and look for the retval = 3 case. helps