Server rewrites. Usually they work adding rules to Apache .htaccess.

On the other hand, this trick was mostly useful years ago when shared hosting plans were really underpowered.

As of today, with improvements of both PHP 7.x and general server performance, even a cache system that uses PHP very early (before any DB connection) to load a pre-rendered html cache file goes a long way in terms of number of pages being served.

Actually, if this become your bottleneck, the .htaccess trick won't help a lot, and you would still look in tools like memcached, redis or reverse proxies to improve things.

So I don't normally setup WP sites, but I have as a favour. A caching plugin just generates the HTML files and you configure NGinX / Apache to the appropriate directory. Historically I think most did it via .htaccess w/ Apache for shared hosts, but I've only configured it w/ NGinX. E.g. https://www.nginx.com/blog/9-tips-for-improving-wordpress-pe...

I think a lot of third-party hosts provide this out of the box, maybe even using their own CDN. WP is so popular that it's be difficult not to find a service that handled it all for you so long as you have room in the budget.

A lot of them do it via special htaccess rules. Check the cache first for an html file, otherwise, fall back to PHP. If not, there may be a little php code running but generally much less than a “normal” request.

>I'd be very curious how a WP plugin is managing this.

If you don't know how the cache plugins do this, it's pretty obvious you are not very knowledgable about WordPress site operations. Please stop spouting falsehoods here.