[wp-trac] [WordPress Trac] #47884: Unable to remove "counts" from non persistent cache groups

[WordPress Trac]

#47884: Unable to remove "counts" from non persistent cache groups
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 Reporter:  Maciej Laskowski          |       Owner:  (none)
     Type:  defect (bug)              |      Status:  assigned
 Priority:  normal                    |   Milestone:  Awaiting Review
Component:  Cache API                 |     Version:  2.6
 Severity:  normal                    |  Resolution:
 Keywords:  dev-feedback 2nd-opinion  |     Focuses:  performance
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Changes (by desrosj):

 * keywords:  dev-feedback => dev-feedback 2nd-opinion
 * version:  3.0 => 2.6


Comment:

 @maciej-laskowski Welcome to Trac!

 For the time being, I think this could be solved by modifying the drop-in.
 Looking at the drop-in you linked to, it seems that you could just check
 if `counts` is a value in `WP_Object_Cache::add_non_persistent_groups()`
 ([https://github.com/tillkruss/redis-
 cache/blob/9e7cebb19daeca070c6a793ae846d77c7b9aa69f/includes/object-
 cache.php#L1312 this line]) and remove it before updating the list of
 groups.

 As for fixing this in Core, I don't know much about the history of the
 groups coded to not persist with `wp_cache_add_non_persistent_groups()`.
 I'd love to get some feedback from others a bit more experienced with the
 history (maybe @boonebgorges, @spacedmonkey?), but I believe that the
 cache entries in these groups are not reliably invalidated. Looking back,
 this function was added in [7986] (see #6740). My hunch is that you will
 have issues with cache invalidation if you are not very careful with this.

 Side note: the code block you linked to is in a conditional that checks
 for the existence of `wp_cache_add_global_groups()`, but assumes the
 existence of `wp_cache_add_non_persistent_groups()`. It may be good to add
 a `function_exists( 'wp_cache_add_non_persistent_groups' )` check there as
 a precaution (maybe with a `_doing_it_wrong()`?).

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Ticket URL: <https://core.trac.wordpress.org/ticket/47884#comment:3>
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