Caching
The Gatsby Blog Starter Kit doesn’t support good caching practices by default. You can fix that by adding a cache buster to your HTML React component (html.js in the root directory). Then you can tell your host that bundle.js or style.css should be cached by browsers for a long time.
// outside the HTML component
const now = new Date();
const buster = now.getTime();
// inside its render() method
<script src={`/bundle.js?t=${buster}`}/>
https://blog.scottnonnenberg.com/practical-gatsby-js/