+ * @param [in] db open notmuch database
+ * @param [in] mode mode (read only or read-write) for reopened database.
+ *
+ * @retval #NOTMUCH_STATUS_SUCCESS
+ * @retval #NOTMUCH_STATUS_ILLEGAL_ARGUMENT The passed database was not open.
+ * @retval #NOTMUCH_STATUS_XAPIAN_EXCEPTION A Xapian exception occured