Add limit to query in WP_Tax_Query

[spacedmonkey]

The call to get_terms in WP_Tax_Query, does not currently have a limit set. This because some taxonomies are hierarchical and could have nested terms. But for none hierarchical taxonomies, a limit can and should be set. This limit will improve query performance and will improve likely of hitting an existing term query cache.

Trac ticket: https://core.trac.wordpress.org/ticket/55360

[spacedmonkey]

After patch

[spacedmonkey]

Before patch

[spacedmonkey]

I recommend testing this ticket along side #55352.

With this change in place, it means that the early call to get_term_by populates the cache for the taxonomy query. This means one less query per page on tag pages.

Even without this benefit, limiting the query, makes the query return first, as SQL, stop processing once the limit is meet.

[peterwilsoncc]

Linked ​pull request approved, @spacedmonkey are you able to take the honors for commit?

[spacedmonkey]

In 53037:

Taxonomy: Improve performance by taxonomy queries by adding a limitting requested terms.

Add a limit to the number of terms requested in taxonomy queries. This improves the performance of the query and the likelihood of hitting an existing term query cache.

Props Spacedmonkey, peterwilsoncc, flixos90.
Fixes #55360.

Merged into core.

[spacedmonkey]

Dev note ready for ​review.

[spacedmonkey]

Has dev note - ​https://make.wordpress.org/core/2022/04/28/taxonomy-performance-improvements-in-wordpress-6-0/