On 6/25/2019 3:51 AM, Jakub Narebski wrote:
> Jakub Narebski <jnareb@xxxxxxxxx> writes:
>> Derrick Stolee <stolee@xxxxxxxxx> writes:
>>> On 5/20/2019 7:02 AM, Jakub Narebski wrote:
>>>>
>>>> Are there any blockers that prevent the switch to this
>>>> "generation number v2"?
>>>>
>>>> - Is it a problem with insufficient data to choose the correct numbering
>>>> as "generation number v2' (there can be only one)?
>>>> - Is it a problem with selected "generation number v2" being
>>>> incompatibile with gen v2, and Git failing when new version of
>>>> commit-graph is used instead of softly just not using commit-graph?
>>>> - Or is it something else?
> [...]
>
>>> Using the generation number column for the corrected
>>> commit-date offsets (assuming we also guarantee the offset is strictly
>>> increasing from parent to child), these new values will be backwards-
>>> compatible _except_ for 'git commit-graph verify'.
>>
>> O.K., so the "generation number v2 (legacy)" would be incremental and
>> backward-compatibile in use (though not in generation and validation).
>>
>> Do I understand it correctly how it is calculated:
>>
>> corrected_date(C) = max(committer_date(C),
>> max_{P ∈ parents(C)}(corrected_date(P)) + 1)
>> offset(C) = corrected_date(C) - committer_date(C)
>> gen_v2(C) = max(offset(C), max_{P ∈ parents(C)}(gen_v2(P)) + 1)
>
> Do you remember who first came up with this idea for backward
> compatibile corrected commit date offsets (monotonically offset
> corrected date)?
I remember saying that the "corrected commit date" that I had suggested
was weak because it was not backwards-compatible with generation numbers
if you are only looking at the offsets. I don't remember who suggested
simply increasing the offset so they do become backwards-compatible.
>> Do you have benchmark for this "monotonically offset corrected commit
>> date" generation number in https://github.com/derrickstolee/git/commits/reach-perf
>> and https://github.com/derrickstolee/gen-test ?
>
> I guess this will have to wait...
I have not had time to revisit this topic and re-run performance
numbers, sorry.
-Stolee
