Stop concatenating scripts and stylesheets in wp-admin and retire load-scripts.php and load-styles.php

[azaozz]

This functionality was added 14 years ago, #8628. At the time it made the loading of wp-admin quite faster by reducing the number of HTTP requests by more than 50%. The downside is that each wp-admin page has it's own set of concatenated scripts and stylesheets making them harder for caching in browser/network caches. Nevertheless the benefits of the reduced number of requests was greater than the insufficient caching.

This changed when HTTP/2 became more popular. Scripts and stylesheets are loaded much more efficiently there and concatenation is generally not needed. This allows for better browser/network caching and for eventual prioritization. In that terms disabling concatenation of scripts and stylesheets in wp-admin would reduce complexity and improve performance in many cases.

[momo360modena]

And I will add that this proposal will reduce the attack perimeter in terms of WordPress security.

Many security plugins propose to reinforce the parameters of calls to these 2 URLs, because possible source of DDOS attack.

[desrosj]

I think this is worth pursuing. Once we have a working solution, we should gather some performance comparisons to make a comparison between the two approaches.

[markhowellsmead]

The current implementation (in WordPress 6.3) is currently causing the asset generation and concatenation to fail with an HTTP 503 error if less than 1.5 Gb RAM is assigned to the site. See ​https://github.com/WordPress/gutenberg/issues/54294 for fuller details.

[markhowellsmead]

Update from the hosting company: the peak RAM required for this process is 1.9 Gb.