8 ms·

> I actually really like the generalized "smallest/fastest/simplest way to create new file from old file" explanation. You might like that explanation because

> I actually really like the generalized "smallest/fastest/simplest way to create new file from old file" explanation. You might like that explanation because it fits a mental model you may have acquired previously, but at the user interface level, Git stores snapshots. It's not an implementation detail, it's what the entire command line is based on.

DiggyJohnson 3y ago
Aren’t there situations with divergent branches where you end up wanting to apply or rewind commits but cannot do so because applying that function is invalid because the difference between commits is just that, a difference, and not a full snapshot of the repository.
- fl7305 3y ago
  No, the previous post above is correct: > Each commit contains a complete exact snapshot of the entire repository. On the other hand it does contain optimizations to reduce the size of these snapshots in the form of git packs I think the problem that you describe is that the divergent branches have made changes in the same file that cannot be automatically reconciled?
DannyBee 3y ago
Basically all atomic-commit based VCs store snapshots. That's how they achieve atomic commits. Git is copy-on-write, so it's not storing full snapshots either, because it's space prohibitive. All of the storage mechanisms (deltas, etc) are time/space tradeoffs. I don't think there is anything odd about that? It's true in lots of things beyond VCen
tomn 3y ago
> at the user interface level, Git stores snapshots Where in the user interface? All the common commands act like they are working with diffs. It amazes me that people keep repeating this (there's another thread of the same stuff here https://news.ycombinator.com/item?id=38896658#38897488 https://news.ycombinator.com/item?id=38896658#38897488 ). It's like "actually git commits are snapshots not diffs" is such a powerful meme that those who repeat it forget about their day-to-day experience of working with git, in which it tries as hard as possible to hide the snapshots, and let you work with diffs. The onion really has three layers: 2) In the user interface, all common commands work as if commits store a reference to a parent commit and a diff. 1) Commits actually store a reference to a tree (snapshot) and a parent commit; diffs are generated on-demand. 0) Trees (snapshots) may actually be stored in different ways, where "smallest/fastest/simplest way to create new file from old file" makes sense. Most people live comfortably on layer two. Occasionally you might need to know about layer 1 to do something weird, and layer 0 is only really for people interested in implementation details.
- codeflo 3y ago
  It’s not a meme, it’s explained in one of the first chapters of the official documentation, in a section titled “snapshots, not differences”: https://git-scm.com/book/en/v2/Getting-Started-What-is-Git%3F https://git-scm.com/book/en/v2/Getting-Started-What-is-Git%3... You and some others in this comment section are simply wrong about this. Everybody is wrong sometimes, that’s no problem. But your righteous tone (“meme”, “amazes me”) after clearly having spent zero minutes of research is not what I would consider a constructive way to engage in a discussion.
  - tomn 3y ago
    Yeah, i'm sorry about the tone, that wasn't my intent. By meme, i don't mean that it's wrong, it isn't, just that in my opinion it's a thing that people like to repeat because they have heard others say it. That's my only explanation for why someone would say "at the user interface level, Git stores snapshots" when the interface is, i think clearly, mostly about working with commits as changes. > You and some others in this comment section are simply wrong about this. Everybody is wrong sometimes, that’s no problem. About what, exactly? As far as i know, what i wrote is factually accurate (or an opinion, which can not be wrong). Yes, the git manual writes about snapshots, because it's literally true (and sometimes necessary to understand), but it also repeatedly refers to commits as changes, because that is a helpful and equivalent way to think about commits, modulo some details which mostly don't matter.
    - codeflo 3y ago
      > That's my only explanation for why someone would say "at the user interface level, Git stores snapshots" when the interface is, i think clearly, mostly about working with commits as changes. That's what the documentation says, no need to assume a conspiracy. I don't know on what authority you claim to know better, you haven't cited anything. > About what, exactly? As far as i know, what i wrote is factually accurate (or an opinion, which can not be wrong). Opinions about facts can be wrong. I've cited the source, maybe you have a better one than the official documentation, but you haven't given it. > Yes, the git manual writes about snapshots, because it's literally true (and sometimes necessary to understand), but it also repeatedly refers to commits as changes But it doesn't. Again, you didn't cite anything. Conceptually, and in the documentation, changes are always something that's computed after the fact. I've triple checked just now, the official documentation always talks about the changes between commits, or the change introduced by a commit (which means the changes to the parent commit) -- that's fine and in fact exactly the point. It never uses "commit" as a synonym for "change", or claims that a commit somehow stores a change.

DiggyJohnson 3y ago

Aren’t there situations with divergent branches where you end up wanting to apply or rewind commits but cannot do so because applying that function is invalid because the difference between commits is just that, a difference, and not a full snapshot of the repository.

fl7305 3y ago
No, the previous post above is correct: > Each commit contains a complete exact snapshot of the entire repository. On the other hand it does contain optimizations to reduce the size of these snapshots in the form of git packs I think the problem that you describe is that the divergent branches have made changes in the same file that cannot be automatically reconciled?

DannyBee 3y ago

Basically all atomic-commit based VCs store snapshots. That's how they achieve atomic commits. Git is copy-on-write, so it's not storing full snapshots either, because it's space prohibitive. All of the storage mechanisms (deltas, etc) are time/space tradeoffs. I don't think there is anything odd about that? It's true in lots of things beyond VCen

tomn 3y ago

> at the user interface level, Git stores snapshots Where in the user interface? All the common commands act like they are working with diffs. It amazes me that people keep repeating this (there's another thread of the same stuff here https://news.ycombinator.com/item?id=38896658#38897488 https://news.ycombinator.com/item?id=38896658#38897488 ). It's like "actually git commits are snapshots not diffs" is such a powerful meme that those who repeat it forget about their day-to-day experience of working with git, in which it tries as hard as possible to hide the snapshots, and let you work with diffs. The onion really has three layers: 2) In the user interface, all common commands work as if commits store a reference to a parent commit and a diff. 1) Commits actually store a reference to a tree (snapshot) and a parent commit; diffs are generated on-demand. 0) Trees (snapshots) may actually be stored in different ways, where "smallest/fastest/simplest way to create new file from old file" makes sense. Most people live comfortably on layer two. Occasionally you might need to know about layer 1 to do something weird, and layer 0 is only really for people interested in implementation details.

codeflo 3y ago
It’s not a meme, it’s explained in one of the first chapters of the official documentation, in a section titled “snapshots, not differences”: https://git-scm.com/book/en/v2/Getting-Started-What-is-Git%3F https://git-scm.com/book/en/v2/Getting-Started-What-is-Git%3... You and some others in this comment section are simply wrong about this. Everybody is wrong sometimes, that’s no problem. But your righteous tone (“meme”, “amazes me”) after clearly having spent zero minutes of research is not what I would consider a constructive way to engage in a discussion.
- tomn 3y ago
  Yeah, i'm sorry about the tone, that wasn't my intent. By meme, i don't mean that it's wrong, it isn't, just that in my opinion it's a thing that people like to repeat because they have heard others say it. That's my only explanation for why someone would say "at the user interface level, Git stores snapshots" when the interface is, i think clearly, mostly about working with commits as changes. > You and some others in this comment section are simply wrong about this. Everybody is wrong sometimes, that’s no problem. About what, exactly? As far as i know, what i wrote is factually accurate (or an opinion, which can not be wrong). Yes, the git manual writes about snapshots, because it's literally true (and sometimes necessary to understand), but it also repeatedly refers to commits as changes, because that is a helpful and equivalent way to think about commits, modulo some details which mostly don't matter.
  - codeflo 3y ago
    > That's my only explanation for why someone would say "at the user interface level, Git stores snapshots" when the interface is, i think clearly, mostly about working with commits as changes. That's what the documentation says, no need to assume a conspiracy. I don't know on what authority you claim to know better, you haven't cited anything. > About what, exactly? As far as i know, what i wrote is factually accurate (or an opinion, which can not be wrong). Opinions about facts can be wrong. I've cited the source, maybe you have a better one than the official documentation, but you haven't given it. > Yes, the git manual writes about snapshots, because it's literally true (and sometimes necessary to understand), but it also repeatedly refers to commits as changes But it doesn't. Again, you didn't cite anything. Conceptually, and in the documentation, changes are always something that's computed after the fact. I've triple checked just now, the official documentation always talks about the changes between commits, or the change introduced by a commit (which means the changes to the parent commit) -- that's fine and in fact exactly the point. It never uses "commit" as a synonym for "change", or claims that a commit somehow stores a change.