code: func (db *DB) expirer() {
  	tick := time.NewTicker(dbCleanupCycle)
  	defer tick.Stop()
  	for {
  		select {
  		case <-tick.C:
  			db.expireNodes()
  		case <-db.quit:
  			return
  		}
  	}
  }
docs: // expirer should be started in a go routine, and is responsible for looping ad
  // infinitum and dropping stale data from the database.