Berkeley DB Reference Guide: Access Methods
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Berkeley DB Reference Guide: Access Methods

Minimum keys per page (bt_minkey)

A minimum number of keys to be stored on a page can be specified as part of the db_open call to open the database, specifically by setting the bt_minkey element of the DB_INFO structure.

This number is not an absolute minimum, rather it is a guideline and more or less keys may be stored on a page than the value specified. What the implementation does is to divide the page size by the value specified to determine a maximum key length, and keys which are larger than that size are stored in overflow pages instead of in the standard Btree leaf pages.

If no value is specified, a value of 2 is used.