How can I subscribe to updates in an RSS feed?

I want to subscribe to changes on a shopify store’s RSS feed for their products. It seems extremely compute intensive to fetch the rss url every second or even every hour. I know RSS feeds are meant to be subscribed to so how can I make it so that I can get a trigger and update data in my database whenever the rss feed changes? Essentially how does feedly work under the hood? Ofc I can’t use feedly itself since I need to update my db based on updates in the rss feed