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From: Philip Oakley <philipoakley@iee.org>
To: esr@thyrsus.com, Jason Pyeron <jpyeron@pdinc.us>
Cc: git@vger.kernel.org, 'Derrick Stolee' <stolee@gmail.com>
Subject: Re: Finer timestamps and serialization in git
Date: Sun, 19 May 2019 01:16:27 +0100	[thread overview]
Message-ID: <b4b151ba-ab43-445f-6e49-ee8e28b30859@iee.org> (raw)
In-Reply-To: <20190515234034.GB124956@thyrsus.com>



On 16/05/2019 00:40, Eric S. Raymond wrote:
> Jason Pyeron <jpyeron@pdinc.us>:
>> If we take the below example:
>>
>> committer Name <user@domain> 1557948240 -0400
>>
>> and we follow the rule that:
>>
>> 1. any trailing zero after the decimal point MUST be omitted
>> 2. if there are no digits after the decimal point, it MUST be omitted
>>
>> This would allow:
>>
>> committer Name <user@domain> 1557948240 -0400
>> committer Name <user@domain> 1557948240.12 -0400
>>
>> but the following are never allowed:
>>
>> committer Name <user@domain> 1557948240. -0400
>> committer Name <user@domain> 1557948240.000000 -0400
>>
>> By following these rules, all previous commits' hash are unchanged. Future commits made on the top of the second will look like old commit formats. Commits coming from "older" tools will produce valid and mergeable objects. The loss precision has frustrated us several times as well.
> Yes, that's almost exactly what I came up with.  I was concerned with upward
> compatibility in fast-export streams, which reposurgeon ingests and emits.
>
> But I don't quite understand your claim that there's no format
> breakage here, unless you're implying to me that timestamps are already
> stored in the git file system as variable-length strings.  Do they
> really never get translated into time_t?  Good news if so.
Maybe just take some of the object ID bits as being the fractional time 
timestamp. They are effectively random, so should do a reasonable job of 
distinguishing commits in a repeatable manner, even with full round 
tripping via older git versions (as long as the sha1 replicates...)

As I understand it the commit timestamp is actually free text within the 
commit object (try `git cat-file -p <commit_object>), so the issue is 
whether the particular git version is ready to accept the additional 
'dot' factional time notation (future versions could be extended, but I 
think old ones would reject them if I understand the test up thread - 
which would compromise backward compatibility and round tripping).
--
Philip

  reply	other threads:[~2019-05-19  0:16 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-15 19:16 Finer timestamps and serialization in git Eric S. Raymond
2019-05-15 20:16 ` Derrick Stolee
2019-05-15 20:28   ` Jason Pyeron
2019-05-15 21:14     ` Derrick Stolee
2019-05-15 22:07       ` Ævar Arnfjörð Bjarmason
2019-05-16  0:28       ` Eric S. Raymond
2019-05-16  1:25         ` Derrick Stolee
2019-05-20 15:05           ` Michal Suchánek
2019-05-20 16:36             ` Eric S. Raymond
2019-05-20 17:22               ` Derrick Stolee
2019-05-20 21:32                 ` Eric S. Raymond
2019-05-15 23:40     ` Eric S. Raymond
2019-05-19  0:16       ` Philip Oakley [this message]
2019-05-19  4:09         ` Eric S. Raymond
2019-05-19 10:07           ` Philip Oakley
2019-05-15 23:32   ` Eric S. Raymond
2019-05-16  1:14     ` Derrick Stolee
2019-05-16  9:50     ` Ævar Arnfjörð Bjarmason
2019-05-19 23:15       ` Jakub Narebski
2019-05-20  0:45         ` Eric S. Raymond
2019-05-20  9:43           ` Jakub Narebski
2019-05-20 10:08             ` Ævar Arnfjörð Bjarmason
2019-05-20 12:40             ` Jeff King
2019-05-20 14:14             ` Eric S. Raymond
2019-05-20 14:41               ` Michal Suchánek
2019-05-20 22:18                 ` Philip Oakley
2019-05-20 21:38               ` Elijah Newren
2019-05-20 23:12                 ` Eric S. Raymond
2019-05-21  0:08               ` Jakub Narebski
2019-05-21  1:05                 ` Eric S. Raymond
2019-05-15 20:20 ` Ævar Arnfjörð Bjarmason
2019-05-16  0:35   ` Eric S. Raymond
2019-05-16  4:14   ` Jeff King

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