Set the minimum number of keys that will be stored on any single
Btree page.
This value is used to determine which keys will be stored on overflow
pages, i.e. if a key or data item is larger than the underlying database
page size divided by the bt_minkey value, it will be stored on
overflow pages instead of within the page itself. The bt_minkey
value specified must be at least 2; if bt_minkey is not explicitly
set, a value of 2 is used.
The Db::set_bt_minkey interface may only be used to configure Berkeley DB before
the Db::open interface is called.
The Db::set_bt_minkey method either returns a non-zero error value or throws an exception that
encapsulates a non-zero error value on failure, and returns 0 on success.