What does Linus Torvalds mean when he says that Git “never ever” tracks a file? The 2019...
Looking for best latin term for a legal document
In microwave frequencies, do you use a circulator when you need a (near) perfect diode?
Which Sci-Fi work first showed weapon of galactic-scale mass destruction?
What is the best strategy for white in this position?
What is the steepest angle that a canal can be traversable without locks?
What could be the right powersource for 15 seconds lifespan disposable giant chainsaw?
Are there any other methods to apply to solving simultaneous equations?
How long do I have to send payment?
Where does the "burst of radiance" from Holy Weapon originate?
Falsification in Math vs Science
Understanding the implication of what "well-defined" means for the operation in quotient group
Where to refill my bottle in India?
Can distinct morphisms between curves induce the same morphism on singular cohomology?
Are USB sockets on wall outlets live all the time, even when the switch is off?
How to make payment on the internet without leaving a money trail?
JSON.serialize: is it possible to suppress null values of a map?
Deadlock Graph and Interpretation, solution to avoid
Could JWST stay at L2 "forever"?
Inflated grade on resume at previous job, might former employer tell new employer?
How can I create a character who can assume the widest possible range of creature sizes?
Is it possible for the two major parties in the UK to form a coalition with each other instead of a much smaller party?
What does "sndry explns" mean in one of the Hitchhiker's guide books?
Spanish for "widget"
aging parents with no investments
What does Linus Torvalds mean when he says that Git “never ever” tracks a file?
The 2019 Stack Overflow Developer Survey Results Are InGit workflow and rebase vs merge questionsHow to stop tracking and ignore changes to a file in Git?How to make Git “forget” about a file that was tracked but is now in .gitignore?In plain English, what does “git reset” do?Handling file renames in gitsrc refspec master does not match any when pushing commits in gitFind when a file was deleted in GitWhat does the term “porcelain” mean in Git?What does cherry-picking a commit with Git mean?Various ways to remove local Git changes
.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ height:90px;width:728px;box-sizing:border-box;
}
Quoting Linus Torvalds when asked how many files Git can handle during his Tech Talk at Google in 2007 (43:09):
…Git tracks your content. It never ever tracks a single file. You cannot track a file in Git. What you can do is you can track a project that has a single file, but if your project has a single file, sure do that and you can do it, but if you track 10,000 files, Git never ever sees those as individual files. Git thinks everything as the full content. All history in Git is based on the history of the whole project…
(Transcripts here.)
Yet, when you dive into the Git book, the first thing you are told is that a file in Git can be either tracked or untracked. Furthermore, it seems to me like the whole Git experience is geared towards file versioning. When using git diff or git status output is presented on a per file basis. When using git add you also get to choose on a per file basis. You can even review history on a file basis and is lightning fast.
How should this statement be interpreted? In terms of file tracking, how is Git different from other source control systems, such as VCS?
git version-control
edited 2 mins ago
Peter Mortensen
13.9k1987113
asked 2 hours ago
Simón Ramírez AmayaSimón Ramírez Amaya
829
|
show 2 more comments
Quoting Linus Torvalds when asked how many files Git can handle during his Tech Talk at Google in 2007 (43:09):
…Git tracks your content. It never ever tracks a single file. You cannot track a file in Git. What you can do is you can track a project that has a single file, but if your project has a single file, sure do that and you can do it, but if you track 10,000 files, Git never ever sees those as individual files. Git thinks everything as the full content. All history in Git is based on the history of the whole project…
(Transcripts here.)
Yet, when you dive into the Git book, the first thing you are told is that a file in Git can be either tracked or untracked. Furthermore, it seems to me like the whole Git experience is geared towards file versioning. When using git diff or git status output is presented on a per file basis. When using git add you also get to choose on a per file basis. You can even review history on a file basis and is lightning fast.
How should this statement be interpreted? In terms of file tracking, how is Git different from other source control systems, such as VCS?
git version-control
edited 2 mins ago
Peter Mortensen
13.9k1987113
asked 2 hours ago
Simón Ramírez AmayaSimón Ramírez Amaya
829
Context of words.. one tells git to 'track' a file by adding it to the files git cares about, but git doesn't internally 'track' a file.
– user2864740
2 hours ago
reddit.com/r/git/comments/5xmrkv/what_is_a_snapshot_in_git - "For where you are at the moment, I suspect what's more important to realize is that there's a difference between how Git presents files to users and how it deals with them internally. As presented to the user, a snapshot contains complete files, not merely diffs. But internally, yes, Git uses diffs to generate packfiles that efficiently store revisions." (This is sharp contrast to, eg. Subversion.)
– user2864740
2 hours ago
1
Git doesn't track files, it tracks changesets. Most version control systems track files. As an example of how / why this can matter, try to check in an empty directory to git (spolier: you can't, because that's an "empty" changeset).
– Elliott Frisch
2 hours ago
@ElliottFrisch That doesn't sound right. Your description is closer to what e.g. darcs does. Git stores snapshots, not changesets.
– melpomene
2 hours ago
@melpomene From here - Yes, Changesets are supported, and there's some flexibility in creating them. But perhaps the internals are different; that's why it was a comment.
– Elliott Frisch
1 hour ago
|
show 2 more comments
Quoting Linus Torvalds when asked how many files Git can handle during his Tech Talk at Google in 2007 (43:09):
…Git tracks your content. It never ever tracks a single file. You cannot track a file in Git. What you can do is you can track a project that has a single file, but if your project has a single file, sure do that and you can do it, but if you track 10,000 files, Git never ever sees those as individual files. Git thinks everything as the full content. All history in Git is based on the history of the whole project…
(Transcripts here.)
Yet, when you dive into the Git book, the first thing you are told is that a file in Git can be either tracked or untracked. Furthermore, it seems to me like the whole Git experience is geared towards file versioning. When using git diff or git status output is presented on a per file basis. When using git add you also get to choose on a per file basis. You can even review history on a file basis and is lightning fast.
How should this statement be interpreted? In terms of file tracking, how is Git different from other source control systems, such as VCS?
git version-control
edited 2 mins ago
Peter Mortensen
13.9k1987113
asked 2 hours ago
Simón Ramírez AmayaSimón Ramírez Amaya
829
Quoting Linus Torvalds when asked how many files Git can handle during his Tech Talk at Google in 2007 (43:09):
…Git tracks your content. It never ever tracks a single file. You cannot track a file in Git. What you can do is you can track a project that has a single file, but if your project has a single file, sure do that and you can do it, but if you track 10,000 files, Git never ever sees those as individual files. Git thinks everything as the full content. All history in Git is based on the history of the whole project…
(Transcripts here.)
Yet, when you dive into the Git book, the first thing you are told is that a file in Git can be either tracked or untracked. Furthermore, it seems to me like the whole Git experience is geared towards file versioning. When using git diff or git status output is presented on a per file basis. When using git add you also get to choose on a per file basis. You can even review history on a file basis and is lightning fast.
How should this statement be interpreted? In terms of file tracking, how is Git different from other source control systems, such as VCS?
git version-control
git version-control
edited 2 mins ago
Peter Mortensen
13.9k1987113
asked 2 hours ago
Simón Ramírez AmayaSimón Ramírez Amaya
829
edited 2 mins ago
Peter Mortensen
13.9k1987113
asked 2 hours ago
Simón Ramírez AmayaSimón Ramírez Amaya
829
edited 2 mins ago
Peter Mortensen
13.9k1987113
edited 2 mins ago
Peter Mortensen
13.9k1987113
edited 2 mins ago
Peter Mortensen
13.9k1987113
13.9k1987113
asked 2 hours ago
Simón Ramírez AmayaSimón Ramírez Amaya
829
asked 2 hours ago
Simón Ramírez AmayaSimón Ramírez Amaya
829
asked 2 hours ago
Simón Ramírez AmayaSimón Ramírez Amaya
829
829
Context of words.. one tells git to 'track' a file by adding it to the files git cares about, but git doesn't internally 'track' a file.
– user2864740
2 hours ago
reddit.com/r/git/comments/5xmrkv/what_is_a_snapshot_in_git - "For where you are at the moment, I suspect what's more important to realize is that there's a difference between how Git presents files to users and how it deals with them internally. As presented to the user, a snapshot contains complete files, not merely diffs. But internally, yes, Git uses diffs to generate packfiles that efficiently store revisions." (This is sharp contrast to, eg. Subversion.)
– user2864740
2 hours ago
1
Git doesn't track files, it tracks changesets. Most version control systems track files. As an example of how / why this can matter, try to check in an empty directory to git (spolier: you can't, because that's an "empty" changeset).
– Elliott Frisch
2 hours ago
@ElliottFrisch That doesn't sound right. Your description is closer to what e.g. darcs does. Git stores snapshots, not changesets.
– melpomene
2 hours ago
@melpomene From here - Yes, Changesets are supported, and there's some flexibility in creating them. But perhaps the internals are different; that's why it was a comment.
– Elliott Frisch
1 hour ago
|
show 2 more comments
Context of words.. one tells git to 'track' a file by adding it to the files git cares about, but git doesn't internally 'track' a file.
– user2864740
2 hours ago
reddit.com/r/git/comments/5xmrkv/what_is_a_snapshot_in_git - "For where you are at the moment, I suspect what's more important to realize is that there's a difference between how Git presents files to users and how it deals with them internally. As presented to the user, a snapshot contains complete files, not merely diffs. But internally, yes, Git uses diffs to generate packfiles that efficiently store revisions." (This is sharp contrast to, eg. Subversion.)
– user2864740
2 hours ago
1
Git doesn't track files, it tracks changesets. Most version control systems track files. As an example of how / why this can matter, try to check in an empty directory to git (spolier: you can't, because that's an "empty" changeset).
– Elliott Frisch
2 hours ago
@ElliottFrisch That doesn't sound right. Your description is closer to what e.g. darcs does. Git stores snapshots, not changesets.
– melpomene
2 hours ago
@melpomene From here - Yes, Changesets are supported, and there's some flexibility in creating them. But perhaps the internals are different; that's why it was a comment.
– Elliott Frisch
1 hour ago
Context of words.. one tells git to 'track' a file by adding it to the files git cares about, but git doesn't internally 'track' a file.
– user2864740
2 hours ago
Context of words.. one tells git to 'track' a file by adding it to the files git cares about, but git doesn't internally 'track' a file.
– user2864740
2 hours ago
reddit.com/r/git/comments/5xmrkv/what_is_a_snapshot_in_git - "For where you are at the moment, I suspect what's more important to realize is that there's a difference between how Git presents files to users and how it deals with them internally. As presented to the user, a snapshot contains complete files, not merely diffs. But internally, yes, Git uses diffs to generate packfiles that efficiently store revisions." (This is sharp contrast to, eg. Subversion.)
– user2864740
2 hours ago
reddit.com/r/git/comments/5xmrkv/what_is_a_snapshot_in_git - "For where you are at the moment, I suspect what's more important to realize is that there's a difference between how Git presents files to users and how it deals with them internally. As presented to the user, a snapshot contains complete files, not merely diffs. But internally, yes, Git uses diffs to generate packfiles that efficiently store revisions." (This is sharp contrast to, eg. Subversion.)
– user2864740
2 hours ago
1
1
Git doesn't track files, it tracks changesets. Most version control systems track files. As an example of how / why this can matter, try to check in an empty directory to git (spolier: you can't, because that's an "empty" changeset).
– Elliott Frisch
2 hours ago
Git doesn't track files, it tracks changesets. Most version control systems track files. As an example of how / why this can matter, try to check in an empty directory to git (spolier: you can't, because that's an "empty" changeset).
– Elliott Frisch
2 hours ago
@ElliottFrisch That doesn't sound right. Your description is closer to what e.g. darcs does. Git stores snapshots, not changesets.
– melpomene
2 hours ago
@ElliottFrisch That doesn't sound right. Your description is closer to what e.g. darcs does. Git stores snapshots, not changesets.
– melpomene
2 hours ago
@melpomene From here - Yes, Changesets are supported, and there's some flexibility in creating them. But perhaps the internals are different; that's why it was a comment.
– Elliott Frisch
1 hour ago
@melpomene From here - Yes, Changesets are supported, and there's some flexibility in creating them. But perhaps the internals are different; that's why it was a comment.
– Elliott Frisch
1 hour ago
|
show 2 more comments
2 Answers
2
active
oldest
votes
In CVS, history was tracked on a per-file basis. A branch might consist of various files with their own various revisions, each with it's own version number. CVS was based off RCS, which tracked individual files in a similar way.
On the other hand, Git takes snapshots of the state of the whole project. Files are not tracked and versioned independently; a revision in the repository refers to a state of the whole project, not one file.
When Git refers to tracking a file, it means simply that it is to be included in the history of the project. Linus's talk was not referring to tracking files in the Git context, but was contrasting the CVS and RCS model with the snapshot-based model used in Git.
answered 2 hours ago
brian m. carlsonbrian m. carlson
2,021312
add a comment |
I agree with brian m. carlson's answer (and have upvoted it): Linus is indeed distinguishing, at least in part, between file-oriented and commit-oriented version control systems. But I think there is more to it than that.
In my book, which is stalled and might never get finished, I tried to come up with a taxonomy for version control systems. In my taxonomy the term for what we're interested here is the atomicity of the version control system. See what is currently page 22. When a VCS has file-level atomicity, there is in fact a history for each file. The VCS must remember the name of the file and what occurred to it at each point.
Git doesn't do that. Git has only a history of commits—the commit is its unit of atomicity, and the history is the set of commits in the repository. What a commit remembers is the data—a whole tree-full of file names and the contents that go with each of those files—plus some metadata: for instance, who made the commit, when, and why, and the internal Git hash ID of the commit's parent commit. (It is this parent, and the directed acycling graph formed by reading all commits and their parents, that is the history in a repository.)
Note that a VCS can be commit-oriented, yet still store data file-by-file. That's an implementation detail, though sometimes an important one, and Git does not do that either. Instead, each commit records a tree, with the tree object encoding file names, modes (i.e., is this file executable or not?), and a pointer to the actual file content. The content itself is stored independently, in a blob object. Like a commit object, a blob gets a hash ID that is unique to its content—but unlike a commit, which can only appear once, the blob can appear in many commits. So the underlying file content in Git is stored directly as a blob, and then indirectly in a tree object whose hash ID is recorded (directly or indirectly) in the commit object.
When you ask Git to show you a file's history using:
git log [--follow] [starting-point] [--] path/to/file
what Git is really doing is walking the commit history, which is the only history Git has, but not showing you any of these commits unless:
- the commit is a non-merge commit, and
- the parent of that commit also has the file, but the content in the parent differs, or the parent of the commit doesn't have the file at all
(but some of these conditions can be modified via additional git log options, and there's a very difficult to describe side effect called History Simplification that makes Git omit some commits from the history walk entirely). The file history you see here does not exactly exist in the repository, in some sense: instead, it's just a synthetic subset of the real history. You'll get a different "file history" if you use different git log options!
answered 1 hour ago
torektorek
199k18248330
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f55602748%2fwhat-does-linus-torvalds-mean-when-he-says-that-git-never-ever-tracks-a-file%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
In CVS, history was tracked on a per-file basis. A branch might consist of various files with their own various revisions, each with it's own version number. CVS was based off RCS, which tracked individual files in a similar way.
On the other hand, Git takes snapshots of the state of the whole project. Files are not tracked and versioned independently; a revision in the repository refers to a state of the whole project, not one file.
When Git refers to tracking a file, it means simply that it is to be included in the history of the project. Linus's talk was not referring to tracking files in the Git context, but was contrasting the CVS and RCS model with the snapshot-based model used in Git.
answered 2 hours ago
brian m. carlsonbrian m. carlson
2,021312
add a comment |
In CVS, history was tracked on a per-file basis. A branch might consist of various files with their own various revisions, each with it's own version number. CVS was based off RCS, which tracked individual files in a similar way.
On the other hand, Git takes snapshots of the state of the whole project. Files are not tracked and versioned independently; a revision in the repository refers to a state of the whole project, not one file.
When Git refers to tracking a file, it means simply that it is to be included in the history of the project. Linus's talk was not referring to tracking files in the Git context, but was contrasting the CVS and RCS model with the snapshot-based model used in Git.
answered 2 hours ago
brian m. carlsonbrian m. carlson
2,021312
add a comment |
In CVS, history was tracked on a per-file basis. A branch might consist of various files with their own various revisions, each with it's own version number. CVS was based off RCS, which tracked individual files in a similar way.
On the other hand, Git takes snapshots of the state of the whole project. Files are not tracked and versioned independently; a revision in the repository refers to a state of the whole project, not one file.
When Git refers to tracking a file, it means simply that it is to be included in the history of the project. Linus's talk was not referring to tracking files in the Git context, but was contrasting the CVS and RCS model with the snapshot-based model used in Git.
answered 2 hours ago
brian m. carlsonbrian m. carlson
2,021312
In CVS, history was tracked on a per-file basis. A branch might consist of various files with their own various revisions, each with it's own version number. CVS was based off RCS, which tracked individual files in a similar way.
On the other hand, Git takes snapshots of the state of the whole project. Files are not tracked and versioned independently; a revision in the repository refers to a state of the whole project, not one file.
When Git refers to tracking a file, it means simply that it is to be included in the history of the project. Linus's talk was not referring to tracking files in the Git context, but was contrasting the CVS and RCS model with the snapshot-based model used in Git.
answered 2 hours ago
brian m. carlsonbrian m. carlson
2,021312
answered 2 hours ago
brian m. carlsonbrian m. carlson
2,021312
answered 2 hours ago
brian m. carlsonbrian m. carlson
2,021312
answered 2 hours ago
brian m. carlsonbrian m. carlson
2,021312
2,021312
add a comment |
add a comment |
I agree with brian m. carlson's answer (and have upvoted it): Linus is indeed distinguishing, at least in part, between file-oriented and commit-oriented version control systems. But I think there is more to it than that.
In my book, which is stalled and might never get finished, I tried to come up with a taxonomy for version control systems. In my taxonomy the term for what we're interested here is the atomicity of the version control system. See what is currently page 22. When a VCS has file-level atomicity, there is in fact a history for each file. The VCS must remember the name of the file and what occurred to it at each point.
Git doesn't do that. Git has only a history of commits—the commit is its unit of atomicity, and the history is the set of commits in the repository. What a commit remembers is the data—a whole tree-full of file names and the contents that go with each of those files—plus some metadata: for instance, who made the commit, when, and why, and the internal Git hash ID of the commit's parent commit. (It is this parent, and the directed acycling graph formed by reading all commits and their parents, that is the history in a repository.)
Note that a VCS can be commit-oriented, yet still store data file-by-file. That's an implementation detail, though sometimes an important one, and Git does not do that either. Instead, each commit records a tree, with the tree object encoding file names, modes (i.e., is this file executable or not?), and a pointer to the actual file content. The content itself is stored independently, in a blob object. Like a commit object, a blob gets a hash ID that is unique to its content—but unlike a commit, which can only appear once, the blob can appear in many commits. So the underlying file content in Git is stored directly as a blob, and then indirectly in a tree object whose hash ID is recorded (directly or indirectly) in the commit object.
When you ask Git to show you a file's history using:
git log [--follow] [starting-point] [--] path/to/file
what Git is really doing is walking the commit history, which is the only history Git has, but not showing you any of these commits unless:
- the commit is a non-merge commit, and
- the parent of that commit also has the file, but the content in the parent differs, or the parent of the commit doesn't have the file at all
(but some of these conditions can be modified via additional git log options, and there's a very difficult to describe side effect called History Simplification that makes Git omit some commits from the history walk entirely). The file history you see here does not exactly exist in the repository, in some sense: instead, it's just a synthetic subset of the real history. You'll get a different "file history" if you use different git log options!
answered 1 hour ago
torektorek
199k18248330
add a comment |
I agree with brian m. carlson's answer (and have upvoted it): Linus is indeed distinguishing, at least in part, between file-oriented and commit-oriented version control systems. But I think there is more to it than that.
In my book, which is stalled and might never get finished, I tried to come up with a taxonomy for version control systems. In my taxonomy the term for what we're interested here is the atomicity of the version control system. See what is currently page 22. When a VCS has file-level atomicity, there is in fact a history for each file. The VCS must remember the name of the file and what occurred to it at each point.
Git doesn't do that. Git has only a history of commits—the commit is its unit of atomicity, and the history is the set of commits in the repository. What a commit remembers is the data—a whole tree-full of file names and the contents that go with each of those files—plus some metadata: for instance, who made the commit, when, and why, and the internal Git hash ID of the commit's parent commit. (It is this parent, and the directed acycling graph formed by reading all commits and their parents, that is the history in a repository.)
Note that a VCS can be commit-oriented, yet still store data file-by-file. That's an implementation detail, though sometimes an important one, and Git does not do that either. Instead, each commit records a tree, with the tree object encoding file names, modes (i.e., is this file executable or not?), and a pointer to the actual file content. The content itself is stored independently, in a blob object. Like a commit object, a blob gets a hash ID that is unique to its content—but unlike a commit, which can only appear once, the blob can appear in many commits. So the underlying file content in Git is stored directly as a blob, and then indirectly in a tree object whose hash ID is recorded (directly or indirectly) in the commit object.
When you ask Git to show you a file's history using:
git log [--follow] [starting-point] [--] path/to/file
what Git is really doing is walking the commit history, which is the only history Git has, but not showing you any of these commits unless:
- the commit is a non-merge commit, and
- the parent of that commit also has the file, but the content in the parent differs, or the parent of the commit doesn't have the file at all
(but some of these conditions can be modified via additional git log options, and there's a very difficult to describe side effect called History Simplification that makes Git omit some commits from the history walk entirely). The file history you see here does not exactly exist in the repository, in some sense: instead, it's just a synthetic subset of the real history. You'll get a different "file history" if you use different git log options!
answered 1 hour ago
torektorek
199k18248330
add a comment |
I agree with brian m. carlson's answer (and have upvoted it): Linus is indeed distinguishing, at least in part, between file-oriented and commit-oriented version control systems. But I think there is more to it than that.
In my book, which is stalled and might never get finished, I tried to come up with a taxonomy for version control systems. In my taxonomy the term for what we're interested here is the atomicity of the version control system. See what is currently page 22. When a VCS has file-level atomicity, there is in fact a history for each file. The VCS must remember the name of the file and what occurred to it at each point.
Git doesn't do that. Git has only a history of commits—the commit is its unit of atomicity, and the history is the set of commits in the repository. What a commit remembers is the data—a whole tree-full of file names and the contents that go with each of those files—plus some metadata: for instance, who made the commit, when, and why, and the internal Git hash ID of the commit's parent commit. (It is this parent, and the directed acycling graph formed by reading all commits and their parents, that is the history in a repository.)
Note that a VCS can be commit-oriented, yet still store data file-by-file. That's an implementation detail, though sometimes an important one, and Git does not do that either. Instead, each commit records a tree, with the tree object encoding file names, modes (i.e., is this file executable or not?), and a pointer to the actual file content. The content itself is stored independently, in a blob object. Like a commit object, a blob gets a hash ID that is unique to its content—but unlike a commit, which can only appear once, the blob can appear in many commits. So the underlying file content in Git is stored directly as a blob, and then indirectly in a tree object whose hash ID is recorded (directly or indirectly) in the commit object.
When you ask Git to show you a file's history using:
git log [--follow] [starting-point] [--] path/to/file
what Git is really doing is walking the commit history, which is the only history Git has, but not showing you any of these commits unless:
- the commit is a non-merge commit, and
- the parent of that commit also has the file, but the content in the parent differs, or the parent of the commit doesn't have the file at all
(but some of these conditions can be modified via additional git log options, and there's a very difficult to describe side effect called History Simplification that makes Git omit some commits from the history walk entirely). The file history you see here does not exactly exist in the repository, in some sense: instead, it's just a synthetic subset of the real history. You'll get a different "file history" if you use different git log options!
answered 1 hour ago
torektorek
199k18248330
I agree with brian m. carlson's answer (and have upvoted it): Linus is indeed distinguishing, at least in part, between file-oriented and commit-oriented version control systems. But I think there is more to it than that.
In my book, which is stalled and might never get finished, I tried to come up with a taxonomy for version control systems. In my taxonomy the term for what we're interested here is the atomicity of the version control system. See what is currently page 22. When a VCS has file-level atomicity, there is in fact a history for each file. The VCS must remember the name of the file and what occurred to it at each point.
Git doesn't do that. Git has only a history of commits—the commit is its unit of atomicity, and the history is the set of commits in the repository. What a commit remembers is the data—a whole tree-full of file names and the contents that go with each of those files—plus some metadata: for instance, who made the commit, when, and why, and the internal Git hash ID of the commit's parent commit. (It is this parent, and the directed acycling graph formed by reading all commits and their parents, that is the history in a repository.)
Note that a VCS can be commit-oriented, yet still store data file-by-file. That's an implementation detail, though sometimes an important one, and Git does not do that either. Instead, each commit records a tree, with the tree object encoding file names, modes (i.e., is this file executable or not?), and a pointer to the actual file content. The content itself is stored independently, in a blob object. Like a commit object, a blob gets a hash ID that is unique to its content—but unlike a commit, which can only appear once, the blob can appear in many commits. So the underlying file content in Git is stored directly as a blob, and then indirectly in a tree object whose hash ID is recorded (directly or indirectly) in the commit object.
When you ask Git to show you a file's history using:
git log [--follow] [starting-point] [--] path/to/file
what Git is really doing is walking the commit history, which is the only history Git has, but not showing you any of these commits unless:
- the commit is a non-merge commit, and
- the parent of that commit also has the file, but the content in the parent differs, or the parent of the commit doesn't have the file at all
(but some of these conditions can be modified via additional git log options, and there's a very difficult to describe side effect called History Simplification that makes Git omit some commits from the history walk entirely). The file history you see here does not exactly exist in the repository, in some sense: instead, it's just a synthetic subset of the real history. You'll get a different "file history" if you use different git log options!
answered 1 hour ago
torektorek
199k18248330
answered 1 hour ago
torektorek
199k18248330
answered 1 hour ago
torektorek
199k18248330
answered 1 hour ago
torektorek
199k18248330
199k18248330
add a comment |
add a comment |
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f55602748%2fwhat-does-linus-torvalds-mean-when-he-says-that-git-never-ever-tracks-a-file%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Context of words.. one tells git to 'track' a file by adding it to the files git cares about, but git doesn't internally 'track' a file.
– user2864740
2 hours ago
reddit.com/r/git/comments/5xmrkv/what_is_a_snapshot_in_git - "For where you are at the moment, I suspect what's more important to realize is that there's a difference between how Git presents files to users and how it deals with them internally. As presented to the user, a snapshot contains complete files, not merely diffs. But internally, yes, Git uses diffs to generate packfiles that efficiently store revisions." (This is sharp contrast to, eg. Subversion.)
– user2864740
2 hours ago
1
Git doesn't track files, it tracks changesets. Most version control systems track files. As an example of how / why this can matter, try to check in an empty directory to git (spolier: you can't, because that's an "empty" changeset).
– Elliott Frisch
2 hours ago
@ElliottFrisch That doesn't sound right. Your description is closer to what e.g. darcs does. Git stores snapshots, not changesets.
– melpomene
2 hours ago
@melpomene From here - Yes, Changesets are supported, and there's some flexibility in creating them. But perhaps the internals are different; that's why it was a comment.
– Elliott Frisch
1 hour ago