GitLab

UUID values

  llllllll-mmmm-Vhhh-vsss-nnnnnnnnnnnn

are now stored as

  nnnnnnnnnnnn-vsss-Vhhh-mmmm-llllllll

inside the record:

- the groups (segments separated by dash) are reordered right-to-left.
- the bytes inside the groups are not reordered (stored as before,
  in big-endian format).

This provides a better sorting order: the earlier UUID was generated,
the higher it appears in the ORDER BY output.

Also, this change enables a good key prefix compression,
because the constant part is now in the beginning, while
the non-constant part (the timestamp) is in the end.