[wp-trac] [WordPress Trac] #60764: Translation file cache never expires, causes issues for atomic filesystems

[WordPress Trac]

#60764: Translation file cache never expires, causes issues for atomic filesystems
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 Reporter:  dd32          |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  I18N          |    Version:  trunk
 Severity:  normal        |   Keywords:
  Focuses:                |
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 In #58919 caching was added for the `.mo` file lookups to use a persistent
 cache.

 The only ways that this cache is cleared are:
  - When the language pack installer upgrades the files
  - When the persistent cache expires, the code specifically specifies no
 expiry.

 External object caches have various limits on what a "no expiry" cache is,
 with some persisting it literally forever, and others limiting it to a
 month.

 Unfortunately, due to this potentially very long cache, for systems which
 do not use  the language pack installer, this can cause new translation
 files to never be picked up.

 For example, on a system with an atomic filesystem, where WordPress cannot
 modify the files directly and files are remotely deployed, the file
 modifications might occur in a `wp-cli` instance on a staging environment
 which doesn't use the production cache.

 Additionally; The `translations` group is defined as per-site, and not
 per-WordPress instance, this causes a language pack update on the main
 site (`blog_id=1`) to clear the cache, but on a second site (`blog_id=2`)
 to still have the old file cache.

 I also observe; The `translations` group doesn't appear to be used
 anywhere else, given the only content of this is a key which is dynamic,
 it makes more sense to use a unique group with dynamic keys. For example,
 here's an example of a current key, and what I'd expect:
 {{{
 {flush_group}:{blog_id}:{group}:{key}
 1701761180267934:40:translations:cached_mo_files_a505c11b7ff533560642ea0d95447745
 # current
 1701761180267934:40:translation_files:a505c11b7ff533560642ea0d95447745 #
 with the group alteration
 1701761180267934:translation_files:a505c11b7ff533560642ea0d95447745 # With
 the group alteration, and per-instance rather than per-blog
 }}}

 I propose:
  - An explicit expiry be added to the `cached_mo_files_*` cache. I would
 say an hour is plenty, but a day would also suffice probably
  - The group be renamed, to `translation_files` to remove the key prefix
  - The cache group be defined as a global group

 PR incoming.

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Ticket URL: <https://core.trac.wordpress.org/ticket/60764>
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