Why are logical timestamps only partially orderable?

[sgpinkus]

The Logical Clock doc states:

A logical timestamp is a globally unique identifier, which can be partially ordered. ..

Yet AFAICT the comparison procedure described on this page gives a total ordering. Also the LWW implementation seems to rely on total ordering. Should this say "A logical timestamp is a globally unique identifier, which can be totally ordered. .."?

[marolbrich]

Logical clocks initially only define a partial order. If the session IDs are also used for ordering, it is totally ordered. I think both statements are correct.

[sgpinkus]

The session ID is defined as part of the logical clock.

A logical timestamp is a globally unique identifier, which can be partially ordered. A logical timestamp is a tuple of two values: (1) a session ID; and (2) a sequence counter.

[marolbrich]

You are right. However, the text is correct as well. I guess, the author wanted to stress the point that the causal order defined by the sequence counter defines only a partial order. The use of the session ID to force a total order is necessary but not justified by causality.