code: func (db *DB) triggerPushSubscriptions() {
  	db.pushTriggersMu.RLock()
  	triggers := db.pushTriggers
  	db.pushTriggersMu.RUnlock()
  
  	for _, t := range triggers {
  		select {
  		case t <- struct{}{}:
  		default:
  		}
  	}
  }
docs: // triggerPushSubscriptions is used internally for starting iterations
  // on Push subscriptions. Whenever new item is added to the push index,
  // this function should be called.