[wp-trac] [WordPress Trac] #33885: meta_form performs a potentially expensive query

[WordPress Trac]

#33885: meta_form performs a potentially expensive query
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 Reporter:  jorbin                               |       Owner:  (none)
     Type:  defect (bug)                         |      Status:  new
 Priority:  normal                               |   Milestone:  Future
                                                 |  Release
Component:  Administration                       |     Version:  4.3.1
 Severity:  critical                             |  Resolution:
 Keywords:  has-patch needs-testing needs-unit-  |     Focuses:
  tests                                          |  performance
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Comment (by davelavoie):

 I had issues with a site where we had more than 4 millions rows in the
 postmeta table, and what fixed it was indeed to set the meta_key column to
 VARCHAR(191).

 However, what is puzzling me is that I've set back the type of the
 meta_key to VARCHAR(255) afterwards, and it's still loading fast.

 I've applied the changes with phpMyAdmin, so maybe phpMyAdmin made other
 changes I'm not aware off when updating the type of the column.. Honnestly
 I don't know. But now the type is still set to VARCHAR(255) and there is
 no noticeable slowdown.

 If somebody have a valid explanation for that, I'm all ears!

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Ticket URL: <https://core.trac.wordpress.org/ticket/33885#comment:84>
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