wp_defer_term_counting() │ WP 2.5.0

Let's say we need to add 1000 posts to the database, each of which will be assigned a different category and tags. We have 20 categories and 50 tags on our site, i.e. the same categories and tags will get different posts. Therefore, in this case you can optimize the import code, postponing recalculation of the number of posts for each category and tag.

$posts_data = [ ... ];

// disables recalculation of posts in categories and collects IDs
wp_defer_term_counting( true );

// import
foreach( $posts_data as $post_data ){
	wp_insert_post( $post_data );
}

// recalculate posts in categories for all collected IDs
wp_defer_term_counting( false );

Suppose we have a lot of similar tags and we want to optimize tags - gather all similar tags into groups, select the main tag from them and move all the posts to the main tag and delete the other tags.

You can delete tags and move their posts to the main tag with wp_delete_term() with additional parameters:

$delete_tag = 25;
$main_tag = 15;

wp_delete_term( $delete_tag, 'post_tag', [ 'default'=>$main_tag, 'force_default'=>1 ] );

Function wp_update_term_count() will be called for each moved post. So, for example, if we have 4 tags in a group (one main tag) and three non-main tags contain, for example, 20 posts, then when we delete these 3 tags, 20 posts will go to the main tag and the recount function will be called 20 times.

To avoid this and to call the recalculation function once instead of 20 you can postpone the recalculation:

$delete_tags_groups = [ ... ];

// disables tag post counts and collects tag IDs
wp_defer_term_counting( true );

// tag removal
foreach( $delete_tags_groups as $tags ){
	$main_tag = array_shift( $tags );

	foreach( $tags as $delete_tag ){
		wp_delete_term( $delete_tag, 'post_tag', [ 'default'=>$main_tag, 'force_default'=>1 ] );
	}
}

// recalculate tag posts for all collected tag IDs
wp_defer_term_counting( false );

For example we need to delete 1,000,000 posts, to speed up this process you can use the following code:

wp_suspend_cache_addition( true );
wp_defer_term_counting( true );

$to_delete = [ 15,12,14, ... ];

// disables recalculation of posts in categories and collects IDs
wp_defer_term_counting( true );

// import
foreach( $to_delete as $post_id ){
	wp_delete_post( $post_id, true );
}

// recalculate posts in categories for all collected IDs
wp_defer_term_counting( false );