[wp-trac] [WordPress Trac] #40052: Issue with WP_Cache not invalidating stale cache after an update request

[WordPress Trac]

#40052: Issue with WP_Cache not invalidating stale cache after an update request
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 Reporter:  cookiesowns                  |      Owner:
     Type:  defect (bug)                 |     Status:  new
 Priority:  normal                       |  Milestone:  Awaiting Review
Component:  Cache API                    |    Version:  4.7.3
 Severity:  normal                       |   Keywords:
  Focuses:  administration, performance  |
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 Hi,

 There appears to be an issue with WP_Cache if/when an object-cache has a
 stale value, and you attempt to update that value to the value that
 already exists in the database ( race condition as an example ). The
 object-cache in this case will never be invalidated until the TTL is hit,
 or if/when the cache is flushed.

 This affects high volume sites that has repetitive actions.

 An example of this happens on our site in production on user_meta, where
 quick endpoints fire that requires a set value on user_meta, however
 occasionally redis-cache will not get updated with the new value, even
 though the wp database does have the proper value.

 In this case there's an infinite loop where wp_cache will return the old
 stale value, and the code will correctly attempt to update it to the new
 value, but WP thinks the value is already correct, and thus the object-
 cache will not be updated.

 Potentially related bugs are #26779 & #31245

 An easy solution is to add a wp_cache_delete onto lines 195/196 here:
 https://github.com/WordPress/WordPress/blob/master/wp-
 includes/meta.php#L190-L253

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Ticket URL: <https://core.trac.wordpress.org/ticket/40052>
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