[wp-trac] [WordPress Trac] #44171: Flushing the rewrite rules is "wrong" on the front-end

[WordPress Trac]

#44171: Flushing the rewrite rules is "wrong" on the front-end
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 Reporter:  azaozz       |       Owner:  (none)
     Type:  enhancement  |      Status:  new
 Priority:  normal       |   Milestone:  5.0
Component:  General      |     Version:
 Severity:  normal       |  Resolution:
 Keywords:  dev-note     |     Focuses:
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Comment (by kraftbj):

 Sample first run:
 **Rewrite rules should only be flushed within wp-admin**

 In 5.0 via #44171, rewrite rules can only be flushed within an
 administrative context (wp-admin).

 Processing rewrite rules, generally, is an expensive operation, which is
 why WordPress stores a compiled set of rewrite rules in the database. When
 plugins or themes flush the rewrite rules on the front-end, this requires
 the site to perform the work of compiling the rewrite rules, performing
 two writes to the database, and, by default, updating the .htaccess or
 web.config to continue loading the site.

 At best, this increases the site load time for visitors, but at worst, can
 overload the database and bring the site down depending on the number of
 concurrent visitors.

 Starting in 5.0, a `_doing_it_wrong` notice will occur and the
 `flush_rewrite_rules()` will return early without action if `is_admin` is
 false. Ideally, flushing the rewrite rules should only occur when there
 has been a preceding action impacting rewrite rules, such as plugin or
 theme activation/deactivation. If actively developing a site, plugin, or
 theme, `add_action( 'admin_init', 'flush_rewrite_rules' );` is acceptable.
 This is often best done via a dedicated development plugin to avoid
 accidentally shipping it in production code.

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Ticket URL: <https://core.trac.wordpress.org/ticket/44171#comment:3>
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