Eliminate switch_to_blog() from multisite option/post functions

[soderlind]

Motivation

switch_to_blog() mutates six globals and, on the fallback object-cache implementation, wipes the entire object cache. Several core functions use it internally even though they only need to read or write a single row in a per-site table. This patch replaces those internal switches with direct queries using $wpdb->get_blog_prefix( $blog_id ), which is a pure function — no side-effects, no globals written.

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Files changed

1. ms-blogs.php

New function: _get_option_from_blog() (added before get_blog_option())

• Internal helper that reads a single option from any site's wp_N_options table without switching blog context.
• Fast path: delegates to get_option() when $blog_id === get_current_blog_id().
• Checks wp_cache_get( $blog_id, 'blog-alloptions' ) and blog-notoptions before hitting the DB.
• Falls back to a direct SELECT against $wpdb->get_blog_prefix( $blog_id ) . 'options'.
• Caches misses in blog-notoptions.
• Applies the existing blog_option_{$option} filter.

Refactored: get_blog_option()

- if ( get_current_blog_id() === $id ) {
-     return get_option( $option, $default_value );
- }
- switch_to_blog( $id );
- $value = get_option( $option, $default_value );
- restore_current_blog();
- return apply_filters( "blog_option_{$option}", $value, $id );
+ return _get_option_from_blog( $id, $option, $default_value );

Refactored: add_blog_option()

- switch_to_blog( $id );
- $return = add_option( $option, $value );
- restore_current_blog();
- return $return;
+ $table  = $wpdb->get_blog_prefix( $id ) . 'options';
+ $exists = $wpdb->get_var( ... );      // check if option already exists
+ if ( $exists ) { return false; }
+ $result = $wpdb->insert( $table, ... );
+ wp_cache_delete( $id, 'blog-alloptions' );
+ wp_cache_delete( $id, 'blog-notoptions' );
+ return false !== $result;

Refactored: delete_blog_option()

- switch_to_blog( $id );
- $return = delete_option( $option );
- restore_current_blog();
- return $return;
+ $table  = $wpdb->get_blog_prefix( $id ) . 'options';
+ $result = $wpdb->delete( $table, [ 'option_name' => $option ] );
+ wp_cache_delete( $id, 'blog-alloptions' );
+ wp_cache_delete( $id, 'blog-notoptions' );
+ return false !== $result && $result > 0;

Refactored: update_blog_option()

- switch_to_blog( $id );
- $return = update_option( $option, $value );
- restore_current_blog();
- return $return;
+ $old_value = _get_option_from_blog( $id, $option );
+ if ( $serialized === maybe_serialize( $old_value ) ) { return false; }
+ // $wpdb->update() if exists, $wpdb->insert() if new
+ wp_cache_delete( $id, 'blog-alloptions' );
+ wp_cache_delete( $id, 'blog-notoptions' );
+ return false !== $result;

---

2. class-wp-site.php

Refactored: WP_Site::get_details() (private)

  if ( false === $details ) {
-     switch_to_blog( $this->blog_id );
+     $id = (int) $this->blog_id;
      $details = new stdClass();
      foreach ( get_object_vars( $this ) as $key => $value ) {
          $details->$key = $value;
      }
-     $details->blogname   = get_option( 'blogname' );
-     $details->siteurl    = get_option( 'siteurl' );
-     $details->post_count = get_option( 'post_count' );
-     $details->home       = get_option( 'home' );
-     restore_current_blog();
+     $details->blogname   = _get_option_from_blog( $id, 'blogname' );
+     $details->siteurl    = _get_option_from_blog( $id, 'siteurl' );
+     $details->post_count = _get_option_from_blog( $id, 'post_count', 0 );
+     $details->home       = _get_option_from_blog( $id, 'home' );

---

3. ms-functions.php

Refactored: get_blog_post()

- function get_blog_post( $blog_id, $post_id ) {
-     switch_to_blog( $blog_id );
-     $post = get_post( $post_id );
-     restore_current_blog();
-     return $post;
- }
+ function get_blog_post( $blog_id, $post_id ) {
+     global $wpdb;
+     $blog_id = (int) $blog_id;
+     $post_id = (int) $post_id;
+     if ( get_current_blog_id() === $blog_id ) {
+         return get_post( $post_id );
+     }
+     $table = $wpdb->get_blog_prefix( $blog_id ) . 'posts';
+     $post  = $wpdb->get_row(
+         $wpdb->prepare( "SELECT * FROM `{$table}` WHERE ID = %d LIMIT 1", $post_id )
+     );
+     if ( ! $post ) { return null; }
+     return sanitize_post( new WP_Post( $post ), 'raw' );
+ }

---

4. multisite.php

3 new test methods added:

Test	Covers
test_get_blog_option_does_not_switch_context()	get_blog_option() on another site must not set $GLOBALS['switched'] to true
test_update_blog_option_does_not_switch_context()	update_blog_option() on another site must not set $GLOBALS['switched'] to true
test_wp_site_get_blogname_without_switching()	WP_Site::__get('blogname') returns correct value and doesn't set $GLOBALS['switched']

---

5. site.php

1 new test method added:

Test	Covers
test_get_blog_post_does_not_switch_context()	get_blog_post() returns correct WP_Post when fetching from another site

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Design decisions

• _get_option_from_blog() — prefixed with _ per WordPress convention for internal/private APIs.
• Current-blog fast path preserved in every function — delegates to native get_option() / update_option() / add_option() / delete_option() / get_post() for full filter and cache compatibility.
• Cache groups blog-alloptions and blog-notoptions match the existing WordPress core cache strategy.
• Cache busting — all write functions (add_, update_, delete_) invalidate both cache groups.
• update_blog_option() — compares serialized old/new values and returns false when unchanged, matching update_option() behavior.
• get_blog_post() — returns null on failure (matches documented WP_Post|null return type).

Out of scope

• get_blog_details() (deprecated function at line 249 still uses switch_to_blog)
• wp_initialize_site() / wp_uninitialize_site() — deeper coupling to switched context
• Third-party plugin code

Trac ticket: https://core.trac.wordpress.org/ticket/64863

Use of AI Tools

GitHub Copilot and Opus 4.6 have been used to review the changes.

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