[wp-trac] [WordPress Trac] #57789: Make theme.json related caches persistent

[WordPress Trac]

#57789: Make theme.json related caches persistent
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 Reporter:  flixos90     |       Owner:  (none)
     Type:  enhancement  |      Status:  new
 Priority:  normal       |   Milestone:  6.3
Component:  Themes       |     Version:
 Severity:  normal       |  Resolution:
 Keywords:               |     Focuses:  performance
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Changes (by flixos90):

 * milestone:  Awaiting Review => 6.3


Old description:

> The `theme_json` cache group is currently non-persistent, which means
> that, even when a site uses a persistent object cache, the data in this
> cache group will only be cached ''within'' a single request. In other
> words, there is only a benefit to this caching when a function is called
> several times, at least more than once, in a single request.
>
> Needless to say, we have noticed in the past that parsing `theme.json`
> and running related logic can be expensive, and the preferable outcome
> would be to make those caches persistent so that they also can be cached
> beyond requests.
>
> The biggest challenge to this is to implement proper cache invalidation.
> Originally, within Gutenberg, the cache group was persistent, but it led
> to problems due to:
> * cache invalidation hard to figure out (what are all the events can lead
> to the cached values becoming stale?)
> * caching logic, rather than database values, is not yet a common
> practice in WordPress, and one of the quirks is that e.g. action/filter
> hooks may no longer be run when the logic that contains them is cached,
> which can lead to a clunky developer experience

New description:

 The `theme_json` cache group is currently non-persistent, which means
 that, even when a site uses a persistent object cache, the data in this
 cache group will only be cached ''within'' a single request. In other
 words, there is only a benefit to this caching when a function is called
 several times, at least more than once, in a single request.

 Needless to say, we have noticed in the past that parsing `theme.json` and
 running related logic can be expensive, and the preferable outcome would
 be to make those caches persistent so that they also can be cached beyond
 requests.

 The biggest challenge to this is to implement proper cache invalidation.
 Originally, within Gutenberg, the cache group was persistent, but it led
 to problems due to:
 * cache invalidation hard to figure out (what are all the events can lead
 to the cached values becoming stale?)
 * caching logic, rather than database values, is not yet a common practice
 in WordPress, and one of the quirks is that e.g. action/filter hooks may
 no longer be run when the logic that contains them is cached, which can
 lead to a clunky developer experience

 See related comment
 https://core.trac.wordpress.org/ticket/57648#comment:17

--

Comment:

 This tracking ticket will likely involve several issues and PRs in the
 Gutenberg repository to identify the best approach for the various usages
 of caching related to `theme.json` and the `theme_json` cache group.

 I'm hopeful we can at least make some notable progress here for WordPress
 6.3, so I'll milestone it for that release for now, acknowledging though
 that most of the work will need to happen in the Gutenberg repository, so
 it'll probably be a while until we get a PR here.

 cc @oandregal @spacedmonkey

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Ticket URL: <https://core.trac.wordpress.org/ticket/57789#comment:1>
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