[wp-trac] [WordPress Trac] #54221: _transient_dirsize_cache is set to autoload=yes and kills db performance if it grows (20MB in our case)

[WordPress Trac]

#54221: _transient_dirsize_cache is set to autoload=yes and kills db performance if
it grows (20MB in our case)
--------------------------+-------------------------------------
 Reporter:  archon810     |       Owner:  (none)
     Type:  defect (bug)  |      Status:  new
 Priority:  normal        |   Milestone:  Awaiting Review
Component:  Database      |     Version:  2.8
 Severity:  major         |  Resolution:
 Keywords:                |     Focuses:  multisite, performance
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Changes (by iandunn):

 * focuses:   => multisite, performance
 * version:  5.8.1 => 2.8


Comment:

 Thanks for reporting this!

 I'm assuming the following about your site:

 * it's ''not'' a Multisite instance
 * it doesn't use object caching
 * the site with the 20mb `dirsize_cache` has 207k folders in its upload
 directory
 * sites with fewer upload subfolders have smaller `dirsize_cache` values,
 which are proportional to the # of folders

 Is all of that correct?


 At first glance, it does look like `dirsize_cache` can grow indefinitely
 based on the # of folders. The transient isn't set with an expiration,
 which seems intentional/correct, given the purpose. It also seems like it
 shouldn't be autoloaded, since it's only used on the Dashboard,  file
 upload/deletion, and Site Health.

 It looks like `set_transient()` sets `$autoload` to `yes` for this
 situation, and it doesn't allow the caller to override that. This doesn't
 seem directly related to r49744; it looks like it goes all the way back to
 when the concept of expiration was added to transients in r10603.

 I don't see a ticket for that commit, though, or any documentation in the
 code. It's not obvious to me why `autoload` would be tied to expiration;
 it seems like it should be tied whether the average performance is better
 when it's loaded w/ all the options, or only when needed. Maybe expiration
 was thought to be a good proxy for that?

 `dirsize_cache` was added for Multisite instances when Multisite was
 merged to Core in r12603. It was repurposed for Site Health (both single-
 and Multisite instances) in r45104.

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Ticket URL: <https://core.trac.wordpress.org/ticket/54221#comment:2>
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