[wp-trac] [WordPress Trac] #56992: The Loop displays incorrect data for queries started with `fields => 'id=>parent'`.

[WordPress Trac]

#56992: The Loop displays incorrect data for queries started with `fields =>
'id=>parent'`.
-------------------------------------------------+-------------------------
 Reporter:  peterwilsoncc                        |       Owner:
                                                 |  peterwilsoncc
     Type:  defect (bug)                         |      Status:  reopened
 Priority:  normal                               |   Milestone:  6.8
Component:  Query                                |     Version:  3.1
 Severity:  normal                               |  Resolution:
 Keywords:  dev-feedback has-patch has-unit-     |     Focuses:
  tests                                          |  performance
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Comment (by peterwilsoncc):

 I've put together a PR to change how it's determined whether the method
 needs to walk the array of posts for cache warming of posts and author
 caches.

 Over 1000 iterations of a large loop using various fields settings, the
 performance regression for "all" is recovered.

 Below are the average values for all versions of PHP used in the test
 suite recorded using MariaDB 11.4. The number of queries is for each
 iteration.
 [https://gist.github.com/peterwilsoncc/a8a0934fe3749f69348052f4cf00ee2c
 Data for each version of PHP can be found in this gist].

 ||= Fields     =||= 6.7 Time    =||= 6.7 Queries =||= Trunk Time  =||=
 Trunk Queries =||= Patch time  =||= Patch Queries =||= Trunk - 6.7   =||=
 Patch - 6.7   =||= Patch - trunk  =||
 || all        || 4.364121467 ||         4    || 5.077857733 ||           4
 || 4.390091121 ||       4        || 0.7137362659  || 0.02596965432 ||
 -0.6877666116  ||
 || ids        || 5.359244257 ||       5      || 5.227709651 ||        5
 || 5.20280087  ||        5       || -0.1315346062 || -0.1564433873 ||
 -0.02490878105 ||
 || id, parent || 1.43522051  ||      1       || 5.324584454 ||         5
 || 5.331013381 ||        5       || 3.889363945   || 3.895792872   ||
 0.006428927183 ||

 The performance hit for `id, parent` is only present if a developer starts
 the loop. If they don't start the loop then it's performance shouldn't
 change.

 The [https://github.com/WordPress/wordpress-develop/pull/8495/files#diff-
 1d050668621cbc3028e027d15e68438f4d879dd6e80ba98f9c9f69b9fb5469d0 source
 code changes are in a PR]. The tesst suite changes won't go in as I've
 hacked them to dump data, only run tests I needed and introduced a very
 flakey test to get the timings.

 ----

 The code in [comment:32 comment 32] is a good example of the improvements
 this change makes, on a test install running the 6.7 code with twenty
 twenty one it makes 19 extra database queries than the version of the code
 in trunk.

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Ticket URL: <https://core.trac.wordpress.org/ticket/56992#comment:44>
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