Eliminating shared taxonomy terms in WordPress 4.3

Work on the taxonomy roadmap, started in earnest during the 4.1 dev cycle, continues to chug along for WordPress 4.3. We’ve been focusing on the elimination of shared terms: terms in different taxonomies that share the same term_id and thus the same row in the wp_terms database table. In 4.1, we stopped creating shared terms. In 4.2, we began splitting existing taxonomy terms when those terms were updated.

In 4.3, we’ll take the final step. When a WordPress site upgrades to 4.3, all existing shared terms will be split.

Toward that end, I’d like to make (a) a final warning to plugin authors, and (b) a plea for help from taxonomy mavens and those who maintain very large and complex WordPress installations.

Plugin authors: Dress rehearsal is nearly over

Since 4.2, saving a shared term (via any interface that uses wp_update_term()) causes that term to be split. It’s fairly rare to update a taxonomy term, which has made 4.2 a sort of trial run for authors to ensure that their plugins are ready for the transition. A quick scan of the plugin repo shows that a few dozen authors have taken advantage of this opportunity. I dub these developers Heroes of WordPress and grant them 🌟🌟 many gold stars 🌟🌟. Many authors, however, have neglected to make the necessary updates.

All WP developers should take note that the upgrade to 4.3 is likely to surface many more odd bugs related to shared terms than 4.2 did. Plugin authors are strongly encouraged to review the 4.2 term splitting field guide to understand the potential repercussions for their public plugins as well as their custom client work, and to review techniques for ensuring a smooth transition.

Get involved

The 4.3 ticket for splitting taxonomy terms on WP upgrade, #30261, is sorely in need of developer feedback. The process of splitting shared terms en masse is potentially resource-intensive, especially on sites with very large numbers of terms (and especially with very large numbers of shared terms). The latest patch on the ticket has some optimizations so that sites with many hundreds of shared terms can be migrated in just a few seconds. If you maintain a site with a large number of (shared) taxonomy terms, or if you maintain a WordPress network with a very large number of sites (especially if you have a custom routine for rolling out database updates), your review and testing of the upgrade routine would be much appreciated.


The fun stuff on the taxonomy roadmap – like termmeta – depends on the complete elimination of shared terms. Let’s get the hard stuff done in 4.3, so that we can make all of your taxonomy dreams come true in the next couple releases.

#4-3, #dev-notes, #taxonomy