MySQL Internals Manual  /  ...  /  The Infimum and Supremum Records The Infimum and Supremum Records

"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 infinity). 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.

The InnoDB code comments distinguish between "the infimum and supremum records" and the "user records" (all other kinds).

It's sometimes unclear whether InnoDB considers the infimum and supremum to be part of the header or not. Their size is fixed and their position is fixed, so I guess so.

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