Upsell Product Add-On App can be configured to use browser's session storage to cache Add-Ons and Settings, this can hugely improve load time as app does not have to fetch data from remote storage each time a product page or cart page is loaded. Caching is very common technique used in mordern web apps to improve performance.
If you have just installed the Upsell Product Add-Ons App, firstly create all our necessary Add-Ons and once you are happy with appearance of the add-ons, go to "Settings" page in the App Admin and click on "Cache Add-Ons" Checkbox under Preferences tab, as shown in the screenshot below, then visit your home page and browse to a product page and you will notice a difference in app loading time.
Updating or Changing Add-Ons & Preferences after they are cached.
Once you have configured caching and you need to update the Add-ons or change preferences, you might notice that changes you are making in the App admin is not immediately visible on your site, this is because Add-Ons and Preferenes are cached for a duration of 15 minutes. In order to test your changes perform following steps:
Disable the Caching by un-checking the "Cache Add-Ons" checkbox
Visit your home page with an additional parameter of ?upsell-cache-clear appended to your shop url, so for example your shop url is https://www.MyShop.com and visit the Shop using https://www.MyShop.com?upsell-cache-clear
Now your changes made in App admin will appear, once you are done with making changes re-enable caching by checking the "Cache Add-Ons" checkbox
Will my user get latest Add-Ons?
Add-Ons and Preferences are cached for 15 minutes and will be re-fetched after every 15 minutes.
Also Add-Ons are cached in a single session i.e if a user closes the browser and re-visits, Add-Ons will be re-fetched.