public function deleteAll()
    {
        /* @var $schedules Mage_Cron_Model_Resource_Schedule_Collection */
        $schedules = Mage::getModel('cron/schedule')->getCollection();
        foreach ($schedules as $key => $schedule) { /* @var Aoe_Scheduler_Model_Schedule $schedule */
            $schedule->delete();
        }
        Mage::app()->saveCache(0, Mage_Cron_Model_Observer::CACHE_KEY_LAST_SCHEDULE_GENERATE_AT, array('crontab'), null);
        return $this;
    }