I am creating a chat API for Android developers, but it's slow -- the chat app is getting messages a little bit late.How can I improve the performance of my code?<?phprequire_once('config.php');$sender_id = $_GET['sender_id'];$receive_id = $_GET['receive_id'];$response = array();if($sender_id && $receive_id){        $results = mysql_query(select * from cpo_chat_system where (sender_id = '$sender_id' AND receive_id = '$receive_id') union select * from cpo_chat_system where (sender_id = '$receive_id' AND receive_id = '$sender_id') ORDER BY date ASC, time ASC);        $total_record = mysql_num_rows($results);           if($total_record > 0)        {            $response['success'] = '1';            while($row = mysql_fetch_assoc($results))            {                   $response['user'][] = $row;                 }        }        else        {            $response['success'] = '0';            $response['user']['error'] = 1;            $response['user']['error_msg'] = Not Data Found;        }}echo json_encode($response);?>
PHP Instant Message API
php;performance;api