Re: Finer timestamps and serialization in git

From: Derrick Stolee <stolee@gmail.com>
Date: May 15, 2019, 21:14 UTC
Message-ID: <998895a9-cfbb-c458-cc88-fa1aabed4389@gmail.com>
In-Reply-To: <023b01d50b5c$cbd3cd90$637b68b0$@pdinc.us>

On 5/15/2019 4:28 PM, Jason Pyeron wrote:

> (please don’t cc me)

Ok. I'll "To" you.

Show 9 quoted lines

> 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

This kind of change would probably break old clients trying to read commits from new clients. Ævar's suggestion [1] of additional headers should not create incompatibilities.

> 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.

What problem are you trying to solve where commit date is important? The only use I have for them is "how long has it been since someone made this change?" A question like "when was this change introduced?" is much less important than "in which version was this first released?" This "in which version" is a graph reachability question, not a date question.

I think any attempt to understand Git commits using commit date without using the underling graph topology (commit->parent relationships) is fundamentally broken and won't scale to even moderately-sized teams. I don't even use "git log" without a "--topo-order" or "--graph" option because using a date order puts unrelated changes next to each other. --topo-order guarantees that a path of commits with only one parent and only one child appears in consecutive order.

Thanks, -Stolee

P.S. All of my (overly strong) opinions on using commit date are made more valid when you realize anyone can set GIT_COMMITTER_DATE to get an arbitrary commit date.

[1] https://public-inbox.org/git/871s0zwjv0.fsf@evledraar.gmail.com/T/#t