[wp-trac] [WordPress Trac] #40351: Term post re-counts scale poorly, are common and difficult to avoid

[WordPress Trac]

#40351: Term post re-counts scale poorly, are common and difficult to avoid
-------------------------------------------------+-------------------------
 Reporter:  mattoperry                           |       Owner:  whyisjake
     Type:  enhancement                          |      Status:  reopened
 Priority:  normal                               |   Milestone:  5.6
Component:  Taxonomy                             |     Version:  4.8
 Severity:  normal                               |  Resolution:
 Keywords:  needs-dev-note has-patch has-unit-   |     Focuses:
  tests                                          |  performance
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Comment (by Chouby):

 In Polylang we heavily rely on taxonomies, including taxonomy for terms to
 create languages and translation groups for terms. However [49141]
 introduces an issue in counting for these taxonomies.

 I wrote 2 simple tests to explain what we are doing.

 In this first test, we automatically create a term in a taxomomy
 "term_taxonomy" when we create a tag. This test passes with WordPress 5.6
 beta 1:
 {{{#!php
 function test_wp_set_object_terms_hooked_to_create_term() {
         $args['update_count_callback'] = '_update_generic_term_count';
         register_taxonomy( 'term_taxonomy', 'term', $args );

         add_action( 'create_term', function( $term_id, $tt_id, $taxonomy )
 {
                 if ( 'post_tag' === $taxonomy ) {
                         $term = wp_insert_term( uniqid(), 'term_taxonomy'
 );
                         $lang = $term['term_id'];
                         wp_set_object_terms( $term_id, $lang,
 'term_taxonomy' );
                 }
         }, 10, 3 );

         $tag_id = $this->factory->tag->create();
         $terms = wp_get_object_terms( $tag_id, 'term_taxonomy' );
         $this->assertCount( 1, $terms ); // Check that a term has been
 assigned to the tag.
         $term = reset( $terms );
         $this->assertEquals( 1, $term->count ); // Check the term count.
 }
 }}}

 In this second test, we do the same but the tag is created by
 `wp_insert_post()`. This test passes with WordPress 5.5 but fails wiht 5.6
 beta 1:
 {{{#!php
 <?php
 function
 test_wp_set_object_terms_hooked_to_create_term_in_wp_insert_post() {
         $args['update_count_callback'] = '_update_generic_term_count';
         register_taxonomy( 'term_taxonomy', 'term', $args );

         add_action( 'create_term', function( $term_id, $tt_id, $taxonomy )
 {
                 if ( 'post_tag' === $taxonomy ) {
                         $term = wp_insert_term( uniqid(), 'term_taxonomy'
 );
                         $lang = $term['term_id'];
                         wp_set_object_terms( $term_id, $lang,
 'term_taxonomy' );
                 }
         }, 10, 3 );

         $post_id = $this->factory->post->create( array( 'tags_input' =>
 array( 'my_tag' ) ) );
         $tags = wp_get_post_tags( $post_id );
         $tag = reset( $tags );
         $terms = wp_get_object_terms( $tag->term_id, 'term_taxonomy' );
         $this->assertCount( 1, $terms ); // Check that a term has been
 assigned to the tag.
         $term = reset( $terms );
         $this->assertEquals( 1, $term->count ); // Check the term count,
 fails in WP 5.6.
 }
 }}}

 The issue is caused by the call to `_wp_prevent_term_counting()` by
 `wp_insert_post()`. It's ok for all the terms assigned directly by this
 function, but it breaks the counting of terms assigned in functions hooked
 to actions fired while the counting is prevented.

 I am not sure it would fix all issues but one possible solution for
 Polylang would be to make `_wp_prevent_term_counting()` taxonomy
 dependent. That the term counting would be prevented only for taxonomies
 handled directly by `wp_insert_post()` instead of all taxonomies at the
 same time.

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/40351#comment:42>
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