"Infimum" and "supremum" are real English words but they are
found only in arcane mathematical treatises, and in
InnoDB comments. To
InnoDB, an infimum is lower than the lowest
possible real value (negative infinity) and a supremum is
greater than the greatest possible real value (positive
InnoDB sets up an infimum record
and a supremum record automatically at page-create time, and
never deletes them. They make a useful barrier to navigation
so that "get-prev" won't pass the beginning and "get-next"
won't pass the end. Also, the infimum record can be a dummy
target for temporary record locks.
InnoDB code comments distinguish
between "the infimum and supremum records" and the "user
records" (all other kinds).
It's sometimes unclear whether
considers the infimum and supremum to be part of the header or
not. Their size is fixed and their position is fixed, so I
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