Performance Field Guide for WordPress 6.1

WordPress 6.1 introduces a number of important performance improvements which will have impact in all aspects. The most significant improvements are done in caching WP_Query as well as REST APIREST API The REST API is an acronym for the RESTful Application Program Interface (API) that uses HTTP requests to GET, PUT, POST and DELETE data. It is how the front end of an application (think “phone app” or “website”) can communicate with the data store (think “database” or “file system”)

Improvements to WP_Query

Database queries in WP_Query being cached is a long wanted feature for many developers and finally a dream come true in WordPress 6.1. A couple of new functions will ensure that users cache and linked objects for menu items are now primed while get_page_by_title function will from now on use WP_Query and take the full advantage of all these improvements.

TracTrac An open source project by Edgewall Software that serves as a bug tracker and project management tool for WordPress. tickets holding these changes: #22176, #55716, #55620, #36905.

Improvements to REST API

Priming caches in a single query will significantly improve Posts controller with several new helper functions but that’s not all. User and comments controller will benefit in a similar way while taxonomyTaxonomy A taxonomy is a way to group things together. In WordPress, some common taxonomies are category, link, tag, or post format. and post type controllers are now going to prepare_links only when needed. This control over prepare_links method will be available for custom controllers as well.

Trac tickets holding these changes: #52992, #56019, #56020, #55592, #55593, #55620, #55674, #56272.

Site Health improvements

WordPress 6.1 will have two new Site Health checks – Persistent Object Cache and Page Cache, along with a number of new filters. Find out more in dedicated Dev notedev note Each important change in WordPress Core is documented in a developers note, (usually called dev note). Good dev notes generally include a description of the change, the decision that led to this change, and a description of how developers are supposed to work with that change. Dev notes are published on Make/Core blog during the beta phase of WordPress release cycle. Publishing dev notes is particularly important when plugin/theme authors and WordPress developers need to be aware of those changes.In general, all dev notes are compiled into a Field Guide at the beginning of the release candidate phase..

Trac tickets holding these changes: #56040, #56041.

Improvements to multisitemultisite Used to describe a WordPress installation with a network of multiple blogs, grouped by sites. This installation type has shared users tables, and creates separate database tables for each blog (wp_posts becomes wp_0_posts). See also network, blog, site

In WordPress 6.1 the networknetwork (versus site, blog) options functions have been updated to be consistent with other metadata types, support for register_meta is added, prime caching network options in a single query, string main site ID in network options and more.

Trac tickets holding these changes: #37181, #55802.


The order of action hooksHooks In WordPress theme and development, hooks are functions that can be applied to an action or a Filter in WordPress. Actions are functions performed when a certain event occurs in WordPress. Filters allow you to modify certain functions. Arguments used to hook both filters and actions look the same. is slightly changed in order to gain more control over caching behavior, preloading assets and conditionally executing redirects.

Trac ticketticket Created for both bug reports and feature development on the bug tracker. holding these changes: #56068.

Improvements to Cache APIAPI An API or Application Programming Interface is a software intermediary that allows programs to interact with each other and share data in limited, clearly defined ways.

Cache API improvements bring validating cache keys in WP_Object_Cache methods, deleting cache by group and making a number of private cache priming functions public, and thus, available for usage in plugins and themes.

A valid cache key must be either an integer number or a non-empty string. This will prevent silent failing in wp_cache_*() functions, done by a quick type check and adding a _doing_it_wrong() message if the string is empty, false, or null. Also, a check in update_user_caches() and clean_user_cache() will make sure that the email is not empty before being cached or removed from cache. Read more in #56198.

Several private cache priming functions for various object types are now public and pluginPlugin A plugin is a piece of software containing a group of functions that can be added to a WordPress website. They can extend functionality or add new features to your WordPress websites. WordPress plugins are written in the PHP programming language and integrate seamlessly with WordPress. These can be free in the Plugin Directory or can be cost-based plugin from a third-party and theme authors are encouraged to use these functions to improve the performance of their code by reducing the number of database queries. These functions are:

  • _prime_post_caches()
  • _prime_term_caches()
  • _prime_comment_caches()
  • _prime_network_caches()
  • _prime_site_caches()
  • _get_non_cached_ids()

Read more in #56386.

Introducing wp_cache_flush_group() function

If you wanted to delete cached item with wp_cache_delete you had to specify the item’s ID, or you had to flush the entire cache with wp_cache_flush. WordPress 6.1 introduces a new plugable function called wp_cache_flush_group which removes all cache items in a group, if the object cache implementation supports it.

Introducing wp_cache_supports() function

Developers can now detect if their current implementation of an object cache supports flushing by group, by calling wp_cache_supports( $feature ) which returns true if the feature is supported. Third-party object cache plugins can declare a wp_cache_supports() function and correctly list their supported features:

  • add_multiple
  • set_multiple
  • get_multiple
  • delete_multiple
  • flush_runtime
  • flush_group

Note: The wp_cache_supports() function replaces and supersedes the wp_cache_supports_group_flush() function added in #4476.

Read more in #56605.

Media improvements

WordPress 6.1 will add decoding="async" to image attributes, along with new wp_img_tag_add_decoding_attr() function and wp_img_tag_add_decoding_attr filterFilter Filters are one of the two types of Hooks They provide a way for functions to modify data of other functions. They are the counterpart to Actions. Unlike Actions, filters are meant to work in an isolated manner, and should never have side effects such as affecting global variables and output.. Read more in #53232.

Query-attachments AJAX endpoint now caches the parent post objects. Read more in #56037.

WP_Media_List_Table class will call update_post_parent_caches function in order to prime parent caches in a single database request. Read more in #56036.

Added caching to wp_count_attachments() for better consistency with wp_count_posts(). Read more in #55227.

Avoid duplicated query when retrieving empty posts collections. Read more in #55677.

Post, Post Types improvements

In WordPress 6.1 WP_Posts_List_Table class will call update_post_author_caches function in order to prime post author caches in a single database request. Read more in #56100.

A new filter post_class_taxonomies will allow developers to reduce the number of taxonomies for which classes term classes are generated. Read more in #37114.

Sites running persistent object caching will have result of database queries in _find_post_by_old_slug and _find_post_by_old_date functions, cached. Read more in #36723.


Additional build task copy:block-json will convert and store all block.json files in a single blocks-json.php which will prevent all of this from happening for every blockBlock Block is the abstract term used to describe units of markup that, composed together, form the content or layout of a webpage using the WordPress editor. The idea combines concepts of what in the past may have achieved with shortcodes, custom HTML, and embed discovery into a single consistent API and user experience. on each page load.

Trac ticket holding these changes: #55005.


Identifiers (such as Table and Field names) are escaped with the %i placeholder which will prevent SQL Injection Vulnerabilities and provide a small performance improvement.

Trac ticket holding these changes: #52506.

Other performance improvements


Performance of WP_List_Table::get_column_info() is improved by adding the primary column to the cached headerHeader The header of your site is typically the first thing people will experience. The masthead or header art located across the top of your page is part of the look and feel of your website. It can influence a visitor’s opinion about your content and you/ your organization’s brand. It may also look different on different screen sizes. values (#34564).

Cron API

In 6.1 wp-cron will be non-blocking for LiteSpeed LSAPI (#54668).


Retain default term option when unregistering taxonomies and adjustments to handling default terms for custom taxonomies (#54472).


Two new actions are wrapping the process of loading a template file (load_template) – wp_before_load_template and wp_after_load_template (#54541).

Script loader

New filter wp_preload_resources enables resource preloading with rel='preload' (#42438).


Prime user metaMeta Meta is a term that refers to the inside workings of a group. For us, this is the team that works on internal WordPress sites like WordCamp Central and Make WordPress. in WP_User_Query (#55594).

Thanks to @spacedmonkey, @tweetythierry, and @tillkruess for peer review.

#6-1, #dev-notes, #dev-notes-6-1, #field-guide, #performance