[wp-trac] [WordPress Trac] #33276: redundant wp_using_ext_object_cache check in get/set_transient

[WordPress Trac]

#33276: redundant wp_using_ext_object_cache check in get/set_transient
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 Reporter:  shmulikk      |      Owner:
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Cache API     |    Version:  4.2.3
 Severity:  normal        |   Keywords:
  Focuses:  performance   |
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 Hello,
 That's my first WP bug report.

 I'm using external memcached plugin.
 I'm testing WP for stability and abusing the system while shutting down
 different components.

 I've found a stability issue when using external object caching plugin,
 not specifically in the external plugin(s) but in WP core.

 If you look at the following methods you see there's a check for whether
 an external object caching plugin exist and if there is - it short circuit
 to directly use it.

 get_transient line 602:
 https://developer.wordpress.org/reference/functions/get_transient/
 set_transient line 667:
 https://developer.wordpress.org/reference/functions/set_transient/

 This check is redundant because if you look at the execution route of when
 such external plugin doesn't exist - it first try to utilize
 wp_cache_set/get as part of the get/set_option or wp_load_alloptions
 functions anyway.

 Now on top of that being redundant it also causes stability and
 performance issues in case where the external plugin fails to work with
 the persistent cache for some reason (i.e. memcached is down). If we
 remove this short circuit / redundant check - we gain a fallback mechanism
 to the options table. So at least we get the original WP behavior instead
 of to a broken state.

 Performance tests I've made on the application without these checks
 resulted with same performance and stability of the WP core even when
 external persistent cache is unhealthy. I couldn't see any regression in
 application functionality to either core or 3rd party plugins we're using.

 Best,
 Shmuel.

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Ticket URL: <https://core.trac.wordpress.org/ticket/33276>
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