An easy way to log session data and queries with Monolog and Hooks in codeigniter. Some of the code is taken from Profiler class in the core of CI. The hook must be post_controller or post_system

gistfile1.php

class LoggerHook
{
    private $CI;
    function __construct()
    {
        $this->CI =& get_instance();
    }

    public function log()
    {
        $logger = new Logger('my_logger');
        
        $logger->pushHandler(new MongoDBHandler(new \MongoClient(), 'test', 'test'));
        

        if (isset($this->CI->session)) {
            $session_data = $this->CI->session->all_userdata();
        } else {
            $session_data = 'No session defined';
        }

        $dbs = array();

        // Let's determine which databases are currently connected to
        foreach (get_object_vars($this->CI) as $CI_object)
        {
            if (is_object($CI_object) && is_subclass_of(get_class($CI_object), 'CI_DB') )
            {
                $dbs[] = $CI_object;
            }
        }

        $queries = array();

        if (count($dbs) > 0){
            foreach ($dbs as $db){
                $driver_name = get_class($db);
                if (count($db->queries) > 0){
                    foreach ($db->queries as $key => $val) {
                        $time = number_format($db->query_times[$key], 4);

                        $queries[$driver_name][] = array('time' => $time , 'query' => $val);
                    }
                }
            }
        } else {
            $queries = 'There is no queries to log';
        }

        $logger->addInfo(
            'Session and queries',
            array(
                'session' => $session_data,
                'database' => $queries'url' => $this->CI->uri->uri_string()
            )
        );
        
    }
}