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