[wp-trac] [WordPress Trac] #14992: When Object Caching is enabled switch_to_blog causes issues with some functions

[WordPress Trac]

#14992: When Object Caching is enabled switch_to_blog causes issues with some
functions
---------------------------+------------------------------------------------
 Reporter:  simonwheatley  |       Owner:                 
     Type:  defect (bug)   |      Status:  new            
 Priority:  normal         |   Milestone:  Awaiting Review
Component:  Multisite      |     Version:                 
 Severity:  normal         |    Keywords:  dev-feedback   
---------------------------+------------------------------------------------
 When you use {{{switch_to_blog}}} with an Object caching plugin installed
 you get incorrect links from {{{home_url}}} and therefore also
 {{{get_permalink}}}.

 To reproduce:

  1. Setup a WP Network using sub-directories with at least two sites
  2. Install an Object caching plugin
  3. Assuming that {{{get_option}}} has been called earlier, thereby
 loading the cache with {{{alloptions}}}, use {{{switch_to_blog}}} then
 {{{get_permalink}}}
  4. {{{get_permalink}}} returns a URL based on the site which was active
 '''before''' you used {{{switch_to_blog}}}

 The problem seems to be that the Object cache caches {{{alloptions}}}, but
 these aren't refreshed or switched when {{{switch_to_blog}}} is used (at
 this point a new set of options should be made available).

 I'm using this code to get around it (this is not a patch, obviously):

 {{{
 /**
  * Hooks the WP MS action switch_blog to switch some caches cache when a
 blog
  * is switched to.
  *
  * @param int $blog_id The ID of the blog which has been switched to
  * @param int $prev_blog_id The ID of the blog we were in before switching
  * @return void
  **/
 function kcostb_switch_blog( $blog_id, $prev_blog_id ) {
         // Save the previous alloptions cache
         $prev_alloptions = wp_cache_get( 'alloptions', 'options' );
         // Do we have a previously cached alloptions for the new blog? If
 so,
         // replace the current alloptions cache otherwise delete it.
         if ( $alloptions = wp_cache_get( "alloptions_$blog_id", 'options'
 ) )
                 wp_cache_replace( "alloptions", $alloptions, 'options' );
         else
                 wp_cache_delete( 'alloptions', 'options' );
 }
 add_action( 'switch_blog', 'kcostb_switch_blog', null, 2 );
 }}}

 Questions:

  * Should this be solved by switching caches (as my mini plugin does)?
  * Should we simply delete the {{{alloptions}}} cache when
 {{{switch_to_blog}}} is used?
  * Are there any other areas affected similarly?

 Happy to produce a patch if the first two questions could be advised upon.

 Could be related to #12040

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Ticket URL: <http://core.trac.wordpress.org/ticket/14992>
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