 <p>Try <code>man dbopen</code> for the C level API which describes these flags, as <code>DB_file</code> is really a very thin wrapper around that. </p> <p>The meaning of this flag differs according to which method you use it on, when used with <code>put</code> this means that a value is replaced (rather than added before or after) and needs to be used after an existing search, i.e., after using the <code>seq</code> function at the C level. </p>