Re: Data Services: use cases

[zimoun]

On Mon, 16 Nov 2020 at 21:50, Christopher Baines <mail@cbaines.net> wrote:

>> The first commit producing j5llsz…-ghc-haddock is not
>> 3922208091 but 12dc9f58c4.  And then compare:
>>
>>                 author date              commit date
>> 3922208091|Thu Jul 23 14:03:19 2020|Fri Jul 24 14:21:31 2020
>> 12dc9f58c4|Fri Jul 24 09:56:25 2020|Fri Jul 24 14:21:30 2020
>>
>> I have not checked what guix-commits says.  Maybe the mess is
>> overthere.
>
> The author date and commit date won't necessarily match the date
> whatever branch is updated (and it's when that branch was updated that
> the Guix Data Service tries to store).

Yes.

> Generally, the author date will match or precede the commit date, which
> will match or precede the date the commit hit whatever branch.

Yes.


> Taking 3922208091 as an example, I pulled the commit dates in UTC [1]:
>
> AuthorDate:        Thu Jul 23 12:03:19 2020
> CommitDate:        Fri Jul 24 12:21:31 2020
> Guix Data Service: 2020-07-24 12:22:11 [2]

My point was: 3922208091 could not be the “correct“ and the correct one
could be 12dc9f58c4.  By correct, read the one introducing the output
j5llsz…-ghc-haddock.  And git show says:

                 author date              commit date
 3922208091|Thu Jul 23 14:03:19 2020|Fri Jul 24 14:21:31 2020
 12dc9f58c4|Fri Jul 24 09:56:25 2020|Fri Jul 24 14:21:30 2020

In the final Git tree history, the commit introducing
j5llsz…-ghc-haddock, i.e., changing from one row to another in the
output-history page, is the commit 12dc9f58c4.  Because of this 1 sec.
difference.

The question is what is the header email date?  But…

> 1: TZ=UTC git show --pretty=fuller 3922208091
> 2:
> https://data.guix.gnu.org/revision/39222080911eaf3d7f74effe4467c1a04464aef3

…the revision 12dc9f58c4 is not available.  See:

http://data.guix.gnu.org/revision/12dc9f58c422c06bf9950f21c54ca3df1dc40af1

Maybe that the explanation.  I do not know.


> I think the author date says something about when the commit was
> originally created. Rebasing and adding the Signed-off-by by bit will
> update the commit date (but not the author date). Finally, the Guix
> Data

Exact.

> Service will store when the branch was updated (it uses the date of the
> email as a proxy for this).

Now, after this discussion, I am not convinced anymore that the email
header date is the right thing because we (user) do not have this
information when debugging locally; only the Git checkout.  Anyway.


All is clear and I am ready to move on. :-) Thanks for all the explanations.


Cheers,
simon