Improve performance of X-WP-TotalPages queries

[spacedmonkey]

In the REST API, there is a header field called X-WP-TotalPages. This field is used to understand how many total pages there are to a REST API call.

This does a call to WP_Query / WP_Comment_Query / WP_User_Query and gets the total of number of results for a query. Here are some examples found in core.

• ​class-wp-rest-posts-controller.php
• ​class-wp-rest-global-styles-revisions-controller.php
• ​class-wp-rest-users-controller.php
• ​class-wp-rest-comments-controller.php
• ​class-wp-rest-global-styles-revisions-controller.php

These queries could be improved, by passing different arguments, to the query classes.

For WP_Query requesting only fields 'ids', limiting the query to 1 result, and disable priming of term / meta caches.
For WP_Comment_Query, passing count parameter and disable comment meta priming.
For WP_User_Query, questing only fields 'ids', limiting the query to 1 result and disable priming of user caches.

This change should be simple, as total counts should be covered by existing unit tests.

Trac ticket: https://core.trac.wordpress.org/ticket/62801

[johnbillion]

Which condition does the $total_posts < 1 logic handle? ie. why is the found_posts property not populated in the main query?

[spacedmonkey]

@johnbillion I don't have any context on this one. Maybe @TimothyBlynJacobs @kadamwhite or @rachelbaker would know why this was done.

[joehoyle]

Could it be that an out of bounds query means found_posts is 0? I.e. if I hit ?paged=100 when there is only 10 pages, I guess found_posts even with the FOUND_ROWS() returns 0?

[adamsilverstein]

Thanks for the PR @Sukhendu2002 - is this ready for review (I see it is draft), or do you have any questions? cc: @spacedmonkey

[kadamwhite]

I believe @joehoyle is correct, if you have (say) 12 items and you did page=3, you'd get 0 results back but it's not clear if you've just paged beyond the maximum or if there's no items at all.

[kadamwhite]

If it's considered ready for review by @sukhendu2002 I'm +1 on the patch, it appears to achieve @spacedmonkey's desired improvements

[sukhendu2002]

Replying to adamsilverstein:

Thanks for the PR @Sukhendu2002 - is this ready for review (I see it is draft), or do you have any questions? cc: @spacedmonkey

Sorry for the delay! I've now marked the PR as ready for review. Let me know if you have any feedback.

Hey @spacedmonkey, Thanks for the review! I have also applied the change in the WP_REST_Revisions_Controller class. Take a look when you get a chance. Thanks!

[spacedmonkey]

This looks good. To late to commit in WP 6.8. Adding to WP 6.9 and assigning to me.