framework/web/DbSession.php
public function gcSession($maxLifetime)
    {
        $this->db->createCommand()
            ->delete($this->sessionTable, '[[expire]]<:expire', [':expire' => time()])
            ->execute();

        return true;
    }
public function gcSession($maxLifetime)
    {
        $this->db->createCommand()
            ->delete($this->sessionTable, '[[expire]]<:expire', [':expire' => time()])
            ->execute();

        return true;
    }
Session GC (garbage collection) handler.
@internal Do not call this method directly.
@param int $maxLifetime the number of seconds after which data will be seen as 'garbage' and cleaned up.
@return bool whether session is GCed successfully