[wp-trac] [WordPress Trac] #32649: Index length optimization in 4.2 made one of the core queries unable to use it

[WordPress Trac]

#32649: Index length optimization in 4.2 made one of the core queries unable to use
it
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 Reporter:  viciousjack   |       Owner:
     Type:  defect (bug)  |      Status:  new
 Priority:  normal        |   Milestone:  Awaiting Review
Component:  Database      |     Version:  4.2
 Severity:  normal        |  Resolution:
 Keywords:                |     Focuses:
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Comment (by dd32):

 > And why going back to the uncut index length (as it was prior 4.2) isn't
 an option ?

 The index length was cut to allow a single index be used on both utf8 &
 utf8mb4. MySQL requires (on InnoDB without the `innodb_large_prefix`
 configuration enabled) that the index be a maximum length of 767 bytes,
 which on a utf8mb4 column is 191 characters & 255 characters on a utf8
 column.

 Leaving the index set as unbounded has issues for the utf8 to utf8mb4
 conversion. There's some background in #31869 and #21212

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Ticket URL: <https://core.trac.wordpress.org/ticket/32649#comment:6>
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