[mdwrigh2]

New versions of git will actually go back and generate this information for old commits. This will lead to git being slightly slower when in old repositories until all the commits contain the generation information, but that should happen fairly quickly.

[derrickpetzold]

I was talking about the case where the timestamps are off. I don't think there is any way to fix that.

[ajuc]

You just go the whole way up to the root node counting parents (taking max length when there are many routes), no problem with amiguity. The problem is - it's slow.

[iclelland]

Not necessarily "all the commits", as I understand it (there's some debate in the thread, so I could be wrong) As long as at least one commit in each merged branch has a generation stored, it's simple to compute without going all the way back to all the roots.