Lazy load $wp_query->found_posts

[scribu]

prettyboymp in #10964:

For the most part, the found posts result is only needed for the main loop where paging is involved, yet, most developers don't know to add the 'no_found_rows' parameter to every single WP_Query request where they don't need paging. It would require creating a magic get() method for backwards compatibility, but it can throw a deprecated warning and switch to a real getter implementation.

Similar: #15773

Related: #17066

So, this problem is also related to default Recent Posts widget? I did not find parameter no_found_rows there and pagination is not required. I had some problems with slow queries which disappeared after removing this widget in the past...

Indeed. It sets 'nopaging' => 0 for some reason, although it also sets 'posts_per_page'.

Actually, lazy loading found_posts isn't really possible since the query is dependent on the previously executed query, the one that contains SQL_CALC_FOUND_ROWS.

Would have been nice, though.