library/Rediska/Zend/Session/SaveHandler/Redis.php
public function gc($maxlifetime)
    {
        try {
            return $this->_set->removeByScore(0, time() - $this->getOption('lifetime'));
        } catch(Rediska_Connection_Exec_Exception $e) {
            $this->_deleteSetOrThrowException($e);
        }
    }
public function gc($maxlifetime)
    {
        try {
            return $this->_set->removeByScore(0, time() - $this->getOption('lifetime'));
        } catch(Rediska_Connection_Exec_Exception $e) {
            $this->_deleteSetOrThrowException($e);
        }
    }
Garbage Collection

@param int $maxlifetime
@return true