Before you rush to enable the System - Cache plugin, b please read the following instructions.
Page caching is where Joomla takes a copy of the whole page when it is first displayed.
"It takes snapshots of entire pages including everything - component, modules, plugins and a template. It is the fastest, the widest and the least flexible approach of all caching options" sasy Klas Berlič. You can read more with examples and images in this post by Klas.
When you use a shopping cart, your product pages have a dynamic content. For every visitor, product-pages render different content.
Take, Pricing, for example. In J2Store, you can set different price for different user (customer) groups.
Example: Leather Boots is a product that has a price of USD $25 for a retailer. However, it costs USD $20 for a wholesale customer.
Assume that you have the Page Caching enabled. When a retailer visits Leather Boots page, Joomla takes a copy and saves it. So when a wholesale customer visits the product, he sees the same page as the retailer. Moreover, it has the wrong price (USD 25).
So it is better to have the System - Cache plugin turned OFF when your site deals with a dynamic content.
View caching is controlled by the cache setting in the Global Configuration.
1. Conservative Caching
Conservative Caching is similar to the Page caching, but you have the option to set a lifetime for a cached content. After a lifetime, Joomla refreshes the cache. Nevertheless, it delivers the same content to all users till the cache is refreshed.
This setting again acts the same way as the Page Caching. However, it allows extensions to manage. J2Store's dynamic pages will not have any issues when you have the conservative caching enabled.
IMPORTANT NOTE: If you use Conservative caching, please exclude the J2Store Cart module from caching as it handles dynamic content. In Module settings -> Advanced - > set Caching to No Caching. (Thank you Jay C Burton for pointing this out)
2. Progressive Caching (Not recommended)
This caches the content for each unique visitor. For sites that handle a large number of visitors, this may not be the good option. Because, caching per visitor affects performance. For a smaller site, this is a faster method
IMPORTANT NOTE: Progressive Caching will override module-specific cache settings.
One should enable module cache for modules with static content only and then it works well with conservative caching. Modules with dynamic content such as J2Store Cart should not be cached.