For the Queue access method, specify that the records are of length
re_len.
For the Recno access method, specify that the records are fixed-length,
not byte delimited, and are of length re_len.
Any records added to the database that are less than re_len bytes
long are automatically padded (see Db::set_re_pad for more
information).
Any attempt to insert records into the database that are greater than
re_len bytes long will cause the call to fail immediately and
return an error.
The Db::set_re_len interface may only be used to configure Berkeley DB before
the Db::open interface is called.
The Db::set_re_len 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.