Proper build caching

[jessevdp]

The plugin has to request data from Umbraco for every content item. If a site has 100 content items, that means the plugin has to send 100 GET requests to the remote Umbraco server every time the site is rebuilt. If only a single content item was altered, that means 99% of those requests were unnecessary.

If the site includes a bunch of images or other media files, these are re-downloaded as well—even when they weren't changed.

Proper build caching could make a huge difference here, especially for larger projects.

[jessevdp]

To check if a certain node has been updated since the last build we could include a "last updated" timestamp on every sitemap node. The plugin could save a timestamp for the last build in it's cache and use it to determine if a given node has been updated since the last build, and thus: if it needs to be reloaded.

Perhaps we can create something similar for media (files). Although gatsby-source-filesystem might already do something to cache remote files.

Useful:

• cache helper
• setPluginStatus action

Before hacking away at this I first want to get a better understanding of what is happening already and how caching should be implemented.

[jessevdp]

Note that #3 is also related to caching.