Performance related issues

[jmlnetwork]

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• I've searched for any related issues and avoided creating a duplicate issue.

Please give us a description of what happened

I'm monitoring the site with New Relic APM, and I get some signals that some part of the code related to yoast is taking a lot of time.
Here it is:

wp-content/plugins/wordpress-seo/inc/sitemaps/class-sitemaps.php:102,225,261
On these lines, the redirect method is hooked to pre_get_posts and calls build_sitemap, which calls get_sitemap_links. This function takes a lot of time. Could we mitigate this? Maybe don't have this run every time, but only when needed...

Also, on Ajax calls, Yoast calls a validate_addons function, which takes 329ms.
wp-content/plugins/wordpress-seo/inc/class-addon-manager.php::validate_addons: 451, 130
This is hooked to admin_init but shouldn't be needed on front-end Ajax calls. Do you think we could fix this?

To Reproduce

Step-by-step reproduction instructions

These run every time. There are no specific steps you need to follow; you can check an Ajax action profile and a WP Query call.

Expected results

1. In these situations, the get_sitemap_links method and validate_addons method should not be called.

Actual results

1. The get_sitemap_links and validate_addons are called and take much server time.

[suascat]

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