threads / discuss / 11059

Re: git guidance

Subject: Re: git guidance

## tl;dr

25 messages between Nov 29, 2007 and Aug 28, 2009.

replies: 24people: 12as markdown or json

Jing Xue· Nov 29, 2007, 15:52 UTC · lore
Quoting Al Boldi <a1426z@gawab.com>:
> Sure, browsing is the easy part, but Version Control starts when things
> become writable.

But how is that supposed to work? What happens when you make some changes to a file and save it? Do you want the "git file system" to commit it right aways or wait until you to issue a "commit" command? The first behavior would obviously be wrong, and the second would make the "file system" not operationally transparent anyways. Right?

By the way, the only SCM I have worked with that tries to mount its repository (or a view on top of it) as a file system is ClearCase with its dynamic views. And, between the buggy file system implementation, the intrusion on workflow, and the lack of scalability, at least in the organization I worked for, it turned out to be a horrible, horrible, horrible idea.

Cheers.
-- 
Jing Xue
Linus Torvalds· Nov 29, 2007, 16:19 UTC · re: Jing Xue · lore
On Thu, 29 Nov 2007, Jing Xue wrote:
Show 7 quoted lines
> 
> By the way, the only SCM I have worked with that tries to mount its
> repository (or a view on top of it) as a file system is ClearCase with
> its dynamic views. And, between the buggy file system implementation,
> the intrusion on workflow, and the lack of scalability, at least in
> the organization I worked for, it turned out to be a horrible,
> horrible, horrible idea.

Doing a read-only mount setup tends to be pretty easy, but it's largely pointless except for specialty uses. Ie it's obviously not useful for actual *development*, but it can be useful for some other cases.

For example, a read-only revctrl filesystem can be a _very_ useful thing for test-farms, where you may have hundreds of clients that run tests on possibly different versions at the same time. In situations like that, the read-only mount can actually often be done as a user-space NFS server on some machine.

The advantage is that you don't need to export close to infinite amounts of versions from a "real" filesystem, or make the clients have their own copies. And if you do it as a user-space NFS server (or samba, for that matter), it's even portable, unlike many other approaches. The read-only part also makes 99% of all the complexity go away, and it turns out to be a fairly easy exercise to do.

So I don't think the filesystem approach is _wrong_ per se. But yes, doing it read-write is almost invariably a big mistake. On operatign systems that support a "union mount" approach, it's likely much better to have a read-only revctl thing, and then over-mount a regular filesystem on top of it.

Trying to make it read-write from the revctl engine standpoint is almost certainly totally insane.

				Linus
Al Boldi· Dec 1, 2007, 06:50 UTC · re: Linus Torvalds · lore
Jing Xue wrote:
Show 9 quoted lines
> Quoting Al Boldi <a1426z@gawab.com>:
> > Sure, browsing is the easy part, but Version Control starts when things
> > become writable.
>
> But how is that supposed to work?  What happens when you make some
> changes to a file and save it?  Do you want the "git file system" to
> commit it right aways or wait until you to issue a "commit" command?
> The first behavior would obviously be wrong, and the second would make
> the "file system" not operationally transparent anyways. Right?

Not sure what you mean by operationally transparent? It would be transparent for the updating client, and the rest of the git-users would need to wait for the commit from the updating client; which is ok, as this transparency is not meant to change the server-side git-update semantic.

Linus Torvalds wrote:
Show 7 quoted lines
> On Thu, 29 Nov 2007, Jing Xue wrote:
> > By the way, the only SCM I have worked with that tries to mount its
> > repository (or a view on top of it) as a file system is ClearCase with
> > its dynamic views. And, between the buggy file system implementation,
> > the intrusion on workflow, and the lack of scalability, at least in
> > the organization I worked for, it turned out to be a horrible,
> > horrible, horrible idea.

Judging an idea, based on a flawed implementation, doesn't prove that the idea itself is flawed.

And...
Show 22 quoted lines
> Doing a read-only mount setup tends to be pretty easy, but it's largely
> pointless except for specialty uses. Ie it's obviously not useful for
> actual *development*, but it can be useful for some other cases.
>
> For example, a read-only revctrl filesystem can be a _very_ useful thing
> for test-farms, where you may have hundreds of clients that run tests on
> possibly different versions at the same time. In situations like that, the
> read-only mount can actually often be done as a user-space NFS server on
> some machine.
>
> The advantage is that you don't need to export close to infinite amounts
> of versions from a "real" filesystem, or make the clients have their own
> copies. And if you do it as a user-space NFS server (or samba, for that
> matter), it's even portable, unlike many other approaches. The read-only
> part also makes 99% of all the complexity go away, and it turns out to be
> a fairly easy exercise to do.
>
> So I don't think the filesystem approach is _wrong_ per se. But yes, doing
> it read-write is almost invariably a big mistake. On operatign systems
> that support a "union mount" approach, it's likely much better to have a
> read-only revctl thing, and then over-mount a regular filesystem on top of
> it.

You could probably do that, or you could instead use cp -al. Both would require some hacks to allow some basic version control.

> Trying to make it read-write from the revctl engine standpoint is almost
> certainly totally insane.

Sure, you wouldn't want to change the git-engine update semantics, as that sits on the server and handles all users. But what the git model is currently missing is a client manager. Right now, this is being worked around by replicating the git tree on the client, which still doesn't provide the required transparency.

IOW, git currently only implements the server-side use-case, but fails to deliver on the client-side. By introducing a git-client manager that handles the transparency needs of a single user, it should be possible to clearly isolate update semantics for both the client and the server, each handling their specific use-case.

Thanks!

-- Al

Phillip Susi· Dec 4, 2007, 22:21 UTC · re: Al Boldi · lore
Al Boldi wrote:
> Judging an idea, based on a flawed implementation, doesn't prove that the 
> idea itself is flawed.

It isn't the implementation that is flawed, it is the idea. The entire point of a change control system is that you explicitly define change sets and add comments to the set. The filesystem was designed to allow changes to be made willy-nilly. If your goal is to perform change control only with filesystem semantics, then you have a non starter as their goals are opposing. Requiring an explicit command command is hardly burdensome, and otherwise, a git tree is perfectly transparent to non git aware tools.

Show 5 quoted lines
> Sure, you wouldn't want to change the git-engine update semantics, as that 
> sits on the server and handles all users.  But what the git model is 
> currently missing is a client manager.  Right now, this is being worked 
> around by replicating the git tree on the client, which still doesn't 
> provide the required transparency.

It isn't missing a client manager, it was explicitly designed to not have one, at least not as a distinct entity from a server, because it does not use a client/server architecture. This is very much by design, not a work around.

What transparency are you requiring here? You can transparently read your git tree with all non git aware tools, what other meaning of transparency is there?

Show 5 quoted lines
> IOW, git currently only implements the server-side use-case, but fails to 
> deliver on the client-side.  By introducing a git-client manager that 
> handles the transparency needs of a single user, it should be possible to 
> clearly isolate update semantics for both the client and the server, each 
> handling their specific use-case.

Any talk of client or server makes no sense since git does not use a client/server model. If you wish to use a centralized repository, then git can be set up to transparently push/pull to/from said repository if you wish via hooks or cron jobs.

Al Boldi· Dec 7, 2007, 17:35 UTC · re: Phillip Susi · lore
Phillip Susi wrote:
Show 9 quoted lines
> Al Boldi wrote:
> > IOW, git currently only implements the server-side use-case, but fails
> > to deliver on the client-side.  By introducing a git-client manager that
> > handles the transparency needs of a single user, it should be possible
> > to clearly isolate update semantics for both the client and the server,
> > each handling their specific use-case.
>
> Any talk of client or server makes no sense since git does not use a
> client/server model.

Whether git uses the client/server model or not does not matter; what matters is that there are two distinct use-cases at work here: one on the server/repository, and the other on the client.

> If you wish to use a centralized repository, then
> git can be set up to transparently push/pull to/from said repository if
> you wish via hooks or cron jobs.

Again, this only handles the interface to/from the server/repository, but once you pulled the sources, it leaves you without Version Control on the client.

By pulling the sources into a git-client manager mounted on some dir, it should be possible to let the developer work naturally/transparently in a readable/writeable manner, and only require his input when reverting locally or committing to the server/repository.

Thanks!

-- Al

Andreas Ericsson· Dec 6, 2007, 18:24 UTC · re: Al Boldi · lore
Al Boldi wrote:
Show 14 quoted lines
> Phillip Susi wrote:
>> Al Boldi wrote:
>>> IOW, git currently only implements the server-side use-case, but fails
>>> to deliver on the client-side.  By introducing a git-client manager that
>>> handles the transparency needs of a single user, it should be possible
>>> to clearly isolate update semantics for both the client and the server,
>>> each handling their specific use-case.
>> Any talk of client or server makes no sense since git does not use a
>> client/server model.
> 
> Whether git uses the client/server model or not does not matter; what matters 
> is that there are two distinct use-cases at work here:  one on the 
> server/repository, and the other on the client.  
> 

Git is distributed. The repository is everywhere. No server is actually needed. Many use one anyway since it can be convenient. It's not, however, necessary.

Show 8 quoted lines
>> If you wish to use a centralized repository, then
>> git can be set up to transparently push/pull to/from said repository if
>> you wish via hooks or cron jobs.
> 
> Again, this only handles the interface to/from the server/repository, but 
> once you pulled the sources, it leaves you without Version Control on the 
> client.
> 

No, that's CVS, SVN and other centralized scm's. With git you have perfect version control on each peer. That's the entire idea behind "fully distributed".

Show 5 quoted lines
> By pulling the sources into a git-client manager mounted on some dir, it 
> should be possible to let the developer work naturally/transparently in a 
> readable/writeable manner, and only require his input when reverting locally 
> or committing to the server/repository.
> 

How is that different from what every SCM, including git, is doing today? The user needs to tell the scm when it's time to take a snapshot of the current state. Git is distributed though, so committing is usually not the same as publishing. Is that lack of a single command to commit and publish what's nagging you? If it's not, I completely fail to see what you're getting at, unless you've only ever looked at repositories without a worktree attached, or you think that git should work like an editor's "undo" functionality, which would be quite insane.

-- 
Andreas Ericsson                   andreas.ericsson@op5.se
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231
Al Boldi· Dec 7, 2007, 18:55 UTC · re: Andreas Ericsson · lore
Andreas Ericsson wrote:
Show 19 quoted lines
> Al Boldi wrote:
> > Phillip Susi wrote:
> >> Al Boldi wrote:
> >>> IOW, git currently only implements the server-side use-case, but fails
> >>> to deliver on the client-side.  By introducing a git-client manager
> >>> that handles the transparency needs of a single user, it should be
> >>> possible to clearly isolate update semantics for both the client and
> >>> the server, each handling their specific use-case.
> >>
> >> Any talk of client or server makes no sense since git does not use a
> >> client/server model.
> >
> > Whether git uses the client/server model or not does not matter; what
> > matters is that there are two distinct use-cases at work here:  one on
> > the server/repository, and the other on the client.
>
> Git is distributed. The repository is everywhere. No server is actually
> needed. Many use one anyway since it can be convenient. It's not, however,
> necessary.

When you read server, don't read it as localized; a server can be distributed. What distinguishes a server from an engine is that it has to handle a multi-user use-case. How that is implemented, locally or remotely or distributed, is another issue.

Show 11 quoted lines
> >> If you wish to use a centralized repository, then
> >> git can be set up to transparently push/pull to/from said repository if
> >> you wish via hooks or cron jobs.
> >
> > Again, this only handles the interface to/from the server/repository,
> > but once you pulled the sources, it leaves you without Version Control
> > on the client.
>
> No, that's CVS, SVN and other centralized scm's. With git you have perfect
> version control on each peer. That's the entire idea behind "fully
> distributed".

As explained before in this thread, replicating the git tree on the client still doesn't provide the required transparency.

Show 13 quoted lines
> > By pulling the sources into a git-client manager mounted on some dir, it
> > should be possible to let the developer work naturally/transparently in
> > a readable/writeable manner, and only require his input when reverting
> > locally or committing to the server/repository.
>
> How is that different from what every SCM, including git, is doing today?
> The user needs to tell the scm when it's time to take a snapshot of the
> current state. Git is distributed though, so committing is usually not the
> same as publishing. Is that lack of a single command to commit and publish
> what's nagging you? If it's not, I completely fail to see what you're
> getting at, unless you've only ever looked at repositories without a
> worktree attached, or you think that git should work like an editor's
> "undo" functionality, which would be quite insane.
You need to re-read the thread.
Thanks!

-- Al

Johannes Schindelin· Dec 6, 2007, 20:22 UTC · re: Al Boldi · lore
Hi,
On Fri, 7 Dec 2007, Al Boldi wrote:
Show 20 quoted lines
> Andreas Ericsson wrote:
> > Al Boldi wrote:
> >
> > > By pulling the sources into a git-client manager mounted on some 
> > > dir, it should be possible to let the developer work 
> > > naturally/transparently in a readable/writeable manner, and only 
> > > require his input when reverting locally or committing to the 
> > > server/repository.
> >
> > How is that different from what every SCM, including git, is doing 
> > today? The user needs to tell the scm when it's time to take a 
> > snapshot of the current state. Git is distributed though, so 
> > committing is usually not the same as publishing. Is that lack of a 
> > single command to commit and publish what's nagging you? If it's not, 
> > I completely fail to see what you're getting at, unless you've only 
> > ever looked at repositories without a worktree attached, or you think 
> > that git should work like an editor's "undo" functionality, which 
> > would be quite insane.
> 
> You need to re-read the thread.

I don't know why you write that, and then say thanks. Clearly, what you wrote originally, and what Andreas pointed out, were quite obvious indicators that git already does what you suggest.

You _do_ work "transparently" (whatever you understand by that overused term) in the working directory, unimpeded by git.

And whenever it is time to revert or commit, you cry for help, invoking git.

So either you succeeded in making yourself misunderstood, or Andreas had quite the obvious and correct comment for you.

Not that diffcult, Dscho

Al Boldi· Dec 7, 2007, 04:37 UTC · re: Johannes Schindelin · lore
Johannes Schindelin wrote:
> Hi,
Hi
Show 9 quoted lines
> On Fri, 7 Dec 2007, Al Boldi wrote:
> > You need to re-read the thread.
>
> I don't know why you write that, and then say thanks.  Clearly, what you
> wrote originally, and what Andreas pointed out, were quite obvious
> indicators that git already does what you suggest.
>
> You _do_ work "transparently" (whatever you understand by that overused
> term) in the working directory, unimpeded by git.

If you go back in the thread, you may find a link to a gitfs client that somebody kindly posted. This client pretty much defines the transparency I'm talking about. The only problem is that it's read-only.

To make it really useful, it has to support versioning locally, disconnected from the server repository. One way to implement this, could be by committing every update unconditionally to an on-the-fly created git repository private to the gitfs client.

With this transparently created private scratch repository it should then be possible for the same gitfs to re-expose the locally created commits, all without any direct user-intervention.

Later, this same scratch repository could then be managed by the normal git-management tools/commands to ultimately update the backend git repositories.

BTW:  Sorry for my previous posts that contained the wrong date; it seems 
that hibernation sometimes advances the date by a full 24h.  Has anybody 
noticed this as well?
Thanks!

-- Al

Andreas Ericsson· Dec 7, 2007, 08:40 UTC · re: Al Boldi · lore
Al Boldi wrote:
Show 23 quoted lines
> Johannes Schindelin wrote:
>> Hi,
> 
> Hi
> 
>> On Fri, 7 Dec 2007, Al Boldi wrote:
>>> You need to re-read the thread.
>> I don't know why you write that, and then say thanks.  Clearly, what you
>> wrote originally, and what Andreas pointed out, were quite obvious
>> indicators that git already does what you suggest.
>>
>> You _do_ work "transparently" (whatever you understand by that overused
>> term) in the working directory, unimpeded by git.
> 
> If you go back in the thread, you may find a link to a gitfs client that 
> somebody kindly posted.  This client pretty much defines the transparency 
> I'm talking about.  The only problem is that it's read-only.
> 
> To make it really useful, it has to support versioning locally, disconnected 
> from the server repository.  One way to implement this, could be by 
> committing every update unconditionally to an on-the-fly created git 
> repository private to the gitfs client.
> 

Earlier you said that you need to be able to tell git when you want to make a commit, which means pretty much any old filesystem could serve as gitfs. Now you're saying you want every single update to be committed, which would make it mimic an editor's undo functionality. I still don't get what it is you really want.

Show 8 quoted lines
> With this transparently created private scratch repository it should then be 
> possible for the same gitfs to re-expose the locally created commits, all 
> without any direct user-intervention.
> 
> Later, this same scratch repository could then be managed by the normal 
> git-management tools/commands to ultimately update the backend git 
> repositories.
> 

That's exactly what's happening today. I imagine whoever wrote the gitfs thing did so to facilitate testing, or as some form of intellectual masturbation.

So, to get to the bottom of this, which of the following workflows is it you want git to support?

### WORKFLOW A ### edit, edit, edit edit, edit, edit edit, edit, edit Oops I made a mistake and need to hop back to "current - 12". edit, edit, edit edit, edit, edit publish everything, similar to just tarring up your workdir and sending out ### END WORKFLOW A ###

### WORKFLOW B ### edit, edit, edit ok this looks good, I want to save a checkpoint here edit, edit, edit looks good again. next checkpoint edit, edit, edit oh crap, back to checkpoint 2 edit, edit, edit ooh, that's better. save a checkpoint and publish those checkpoints ### END WORKFLOW B ###

If you could just answer that question and stop writing "transparent" or any synonym thereof six times in each email, we can possibly help you.

As it stands now though, nobody is very interested because you haven't explained how you want this "transparency" of yours to work in an every day scenario.

-- 
Andreas Ericsson                   andreas.ericsson@op5.se
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231
Al Boldi· Dec 7, 2007, 10:53 UTC · re: Andreas Ericsson · lore
Andreas Ericsson wrote:
Show 23 quoted lines
> So, to get to the bottom of this, which of the following workflows is it
> you want git to support?
>
> ### WORKFLOW A ###
> edit, edit, edit
> edit, edit, edit
> edit, edit, edit
> Oops I made a mistake and need to hop back to "current - 12".
> edit, edit, edit
> edit, edit, edit
> publish everything, similar to just tarring up your workdir and sending
> out ### END WORKFLOW A ###
>
> ### WORKFLOW B ###
> edit, edit, edit
> ok this looks good, I want to save a checkpoint here
> edit, edit, edit
> looks good again. next checkpoint
> edit, edit, edit
> oh crap, back to checkpoint 2
> edit, edit, edit
> ooh, that's better. save a checkpoint and publish those checkpoints
> ### END WORKFLOW B ###

### WORKFLOW C ### for every save on a gitfs mounted dir, do an implied checkpoint, commit, or publish (should be adjustable), on its privately created on-the-fly repository. ### END WORKFLOW C ###

For example:
  echo "// last comment on this file" >> /gitfs.mounted/file

should do an implied checkpoint, and make these checkpoints immediately visible under some checkpoint branch of the gitfs mounted dir.

Note, this way the developer gets version control without even noticing, and works completely transparent to any kind of application.

Thanks!

-- Al

Jakub Narebski· Dec 7, 2007, 11:47 UTC · re: Al Boldi · lore
Al Boldi <a1426z@gawab.com> writes:
> Andreas Ericsson wrote:
Show 29 quoted lines
>> So, to get to the bottom of this, which of the following workflows is it
>> you want git to support?
>>
>> ### WORKFLOW A ###
>> edit, edit, edit
>> edit, edit, edit
>> edit, edit, edit
>> Oops I made a mistake and need to hop back to "current - 12".
>> edit, edit, edit
>> edit, edit, edit
>> publish everything, similar to just tarring up your workdir and sending
>> out ### END WORKFLOW A ###
>>
>> ### WORKFLOW B ###
>> edit, edit, edit
>> ok this looks good, I want to save a checkpoint here
>> edit, edit, edit
>> looks good again. next checkpoint
>> edit, edit, edit
>> oh crap, back to checkpoint 2
>> edit, edit, edit
>> ooh, that's better. save a checkpoint and publish those checkpoints
>> ### END WORKFLOW B ###
> 
> ### WORKFLOW C ###
> for every save on a gitfs mounted dir, do an implied checkpoint, commit, or 
> publish (should be adjustable), on its privately created on-the-fly 
> repository.
> ### END WORKFLOW C ###
It looks like it is WORKFLOW A (with the fact that each ',' is file
save stated explicitely rather than implicitely).
 
Show 9 quoted lines
> For example:
> 
>   echo "// last comment on this file" >> /gitfs.mounted/file
> 
> should do an implied checkpoint, and make these checkpoints immediately 
> visible under some checkpoint branch of the gitfs mounted dir.
> 
> Note, this way the developer gets version control without even noticing, and 
> works completely transparent to any kind of application.

Why not use versioning filesystem for that, for example ext3cow (which looks suprisingly git-like, when you take into account that for ext3cow history is linear and centralized, so one can use date or sequential number to name commits).

See GitLinks page on Git Wiki, "Other links" section:
  http://www.ext3cow.com/

Version control system is all about WORKFLOW B, where programmer controls when it is time to commit (and in private repository he/she can then rewrite history to arrive at "Perfect patch series"[*1*]); something that for example CVS failed at, requiring programmer to do a merge if upstream has any changes when trying to commit.

[*1*] I have lost link to post at LKML about rewriting history to
      arrive at perfect patch _series_. IIRC I have found it first
      time on this mailing list. I would be grateful for sending this
      link if you have it. TIA.
-- 
Jakub Narebski
ShadeHawk on #git
Al Boldi· Dec 7, 2007, 19:04 UTC · re: Jakub Narebski · lore
Jakub Narebski wrote:
Show 18 quoted lines
> Al Boldi <a1426z@gawab.com> writes:
> > For example:
> >
> >   echo "// last comment on this file" >> /gitfs.mounted/file
> >
> > should do an implied checkpoint, and make these checkpoints immediately
> > visible under some checkpoint branch of the gitfs mounted dir.
> >
> > Note, this way the developer gets version control without even noticing,
> > and works completely transparent to any kind of application.
>
> Why not use versioning filesystem for that, for example ext3cow
> (which looks suprisingly git-like, when you take into account that
> for ext3cow history is linear and centralized, so one can use date
> or sequential number to name commits).
>
> See GitLinks page on Git Wiki, "Other links" section:
>   http://www.ext3cow.com/

Sure, Linus mentioned the cow idea before in this thread, but you would still need a few hacks to get some basic Version Control features.

Show 5 quoted lines
> Version control system is all about WORKFLOW B, where programmer
> controls when it is time to commit (and in private repository he/she
> can then rewrite history to arrive at "Perfect patch series"[*1*]);
> something that for example CVS failed at, requiring programmer to do
> a merge if upstream has any changes when trying to commit.

Because WORKFLOW C is transparent, it won't affect other workflows. So you could still use your normal WORKFLOW B in addition to WORKFLOW C, gaining an additional level of version control detail at no extra cost other than the git-engine scratch repository overhead.

BTW, is git efficient enough to handle WORKFLOW C?
Thanks!

-- Al

valdis.kletnieks@vt.edu· Dec 7, 2007, 19:36 UTC · re: Al Boldi · lore
On Fri, 07 Dec 2007 22:04:48 +0300, Al Boldi said:
Show 6 quoted lines
> Because WORKFLOW C is transparent, it won't affect other workflows.  So you 
> could still use your normal WORKFLOW B in addition to WORKFLOW C, gaining an 
> additional level of version control detail at no extra cost other than the 
> git-engine scratch repository overhead.
> 
> BTW, is git efficient enough to handle WORKFLOW C?

Imagine the number of commits a 'make clean; make' will do in a kernel tree, as it commits all those .o files... :)

Luke Lu· Dec 7, 2007, 22:07 UTC · re: valdis.kletnieks@vt.edu · lore
On Dec 7, 2007, at 11:36 AM, Valdis.Kletnieks@vt.edu wrote:
Show 15 quoted lines
> On Fri, 07 Dec 2007 22:04:48 +0300, Al Boldi said:
>
>> Because WORKFLOW C is transparent, it won't affect other  
>> workflows.  So you
>> could still use your normal WORKFLOW B in addition to WORKFLOW C,  
>> gaining an
>> additional level of version control detail at no extra cost other  
>> than the
>> git-engine scratch repository overhead.
>>
>> BTW, is git efficient enough to handle WORKFLOW C?
>
> Imagine the number of commits a 'make clean; make' will do in a  
> kernel tree, as
> it commits all those .o files... :)

My guess is that Al is not really a developer (product management/ marketing?), what he has in mind is probably not an SCM but a backup system a la Mac's time machine or Netapp's snapshots that also support disconnected commits. I think that git could be a suitable engine for such systems, after a few tweaks to avoid compressing already compressed blobs like jpeg, mp3 and mpeg etc.

__Luke
Al Boldi· Dec 8, 2007, 04:56 UTC · re: valdis.kletnieks@vt.edu · lore
Valdis.Kletnieks@vt.edu wrote:
Show 10 quoted lines
> On Fri, 07 Dec 2007 22:04:48 +0300, Al Boldi said:
> > Because WORKFLOW C is transparent, it won't affect other workflows.  So
> > you could still use your normal WORKFLOW B in addition to WORKFLOW C,
> > gaining an additional level of version control detail at no extra cost
> > other than the git-engine scratch repository overhead.
> >
> > BTW, is git efficient enough to handle WORKFLOW C?
>
> Imagine the number of commits a 'make clean; make' will do in a kernel
> tree, as it commits all those .o files... :)
.o files???

It probably goes without saying, that gitfs should have some basic configuration file to setup its transparent behaviour, and which would most probably contain an include / exclude file-filter mask, and probably other basic configuration options. But this is really secondary to the implementation, and the question remains whether git is efficient enough.

IOW, how big is the git commit overhead as compared to a normal copy?
Thanks!

-- Al

valdis.kletnieks@vt.edu· Dec 8, 2007, 05:16 UTC · re: Al Boldi · lore
On Sat, 08 Dec 2007 07:56:21 +0300, Al Boldi said:
> It probably goes without saying, that gitfs should have some basic 
> configuration file to setup its transparent behaviour
But then it's not *truly* transparent, is it?

And that leaves another question - if you make a config file that excludes all the .o files - then what's backing the .o files? Those data blocks need to be *someplace*. Maybe you can do something ugly like use unionfs to combine your gitfs with something else to store the other files...

But at that point, you're probably better off just creating a properly designed versioning filesystem.

Al Boldi· Dec 8, 2007, 10:41 UTC · re: valdis.kletnieks@vt.edu · lore
Valdis.Kletnieks@vt.edu wrote:
Show 5 quoted lines
> On Sat, 08 Dec 2007 07:56:21 +0300, Al Boldi said:
> > It probably goes without saying, that gitfs should have some basic
> > configuration file to setup its transparent behaviour
>
> But then it's not *truly* transparent, is it?

Don't mistake transparency with some form of auto-heuristic. Transparency only means that it inserts functionality without impeding your normal workflow.

> And that leaves another question - if you make a config file that excludes
> all the .o files - then what's backing the .o files?  Those data blocks
> need to be *someplace*.  Maybe you can do something ugly like use unionfs
> to combine your gitfs with something else to store the other files...
Or any number of other possible implementation scenarios...
> But at that point, you're probably better off just creating a properly
> designed versioning filesystem.

But gitfs is not about designing a versioning filesystem, it's about designing a transparent interface into git to handle an SCM use-case.

Thanks!

-- Al

Johannes Schindelin· Dec 8, 2007, 11:13 UTC · re: Al Boldi · lore
Hi,
On Fri, 7 Dec 2007, Al Boldi wrote:
Show 14 quoted lines
> Jakub Narebski wrote:
>
> > Version control system is all about WORKFLOW B, where programmer 
> > controls when it is time to commit (and in private repository he/she 
> > can then rewrite history to arrive at "Perfect patch series"[*1*]); 
> > something that for example CVS failed at, requiring programmer to do a 
> > merge if upstream has any changes when trying to commit.
> 
> Because WORKFLOW C is transparent, it won't affect other workflows.  So 
> you could still use your normal WORKFLOW B in addition to WORKFLOW C, 
> gaining an additional level of version control detail at no extra cost 
> other than the git-engine scratch repository overhead.
> 
> BTW, is git efficient enough to handle WORKFLOW C?

The question is not if git is efficient enough to handle workflow C, but if that worflow is efficient enough to help anybody.

Guess what takes me the longest time when committing? The commit message. But it is really helpful, so there is a _point_ in writing one, and there is a _point_ in committing when I do it: it is a point in time where I expect the tree to be in a good shape, to be compilable, and to solve a specific problem which I describe in the commit message.

So I absolutely hate this "transparency". Git _is_ transparent; it does not affect any of my other tools; they still work very well thankyouverymuch.

What your version of "transparency" would do: destroy bisectability, make an absolute gibberish of the history, and more!

Nobody could read the output of "git log" and form an understanding what was done. Nobody could read the commit message for a certain "git blame"d line that she tries to make sense of.

IOW you would revert the whole meaning of the term Source Code Management.

Hth, Dscho

Andreas Ericsson· Dec 7, 2007, 12:30 UTC · re: Al Boldi · lore
Al Boldi wrote:
Show 31 quoted lines
> Andreas Ericsson wrote:
>> So, to get to the bottom of this, which of the following workflows is it
>> you want git to support?
>>
>> ### WORKFLOW A ###
>> edit, edit, edit
>> edit, edit, edit
>> edit, edit, edit
>> Oops I made a mistake and need to hop back to "current - 12".
>> edit, edit, edit
>> edit, edit, edit
>> publish everything, similar to just tarring up your workdir and sending
>> out ### END WORKFLOW A ###
>>
>> ### WORKFLOW B ###
>> edit, edit, edit
>> ok this looks good, I want to save a checkpoint here
>> edit, edit, edit
>> looks good again. next checkpoint
>> edit, edit, edit
>> oh crap, back to checkpoint 2
>> edit, edit, edit
>> ooh, that's better. save a checkpoint and publish those checkpoints
>> ### END WORKFLOW B ###
> 
> ### WORKFLOW C ###
> for every save on a gitfs mounted dir, do an implied checkpoint, commit, or 
> publish (should be adjustable), on its privately created on-the-fly 
> repository.
> ### END WORKFLOW C ###
> 

So you *do* want an editor's undo function, but for an entire filesystem. That's a handy thing to have every now and then, but it's not what git (or any other scm) does.

Show 10 quoted lines
> For example:
> 
>   echo "// last comment on this file" >> /gitfs.mounted/file
> 
> should do an implied checkpoint, and make these checkpoints immediately 
> visible under some checkpoint branch of the gitfs mounted dir.
> 
> Note, this way the developer gets version control without even noticing, and 
> works completely transparent to any kind of application.
> 

One other thing that's fairly important to note is that this can never ever handle changesets, since each write() of each file will be a commit on its own. It's so far from what git does that I think you'd be better off just implementing it from scratch, or looking at a versioned fs, like Jakub suggested in his reply.

You're also neglecting one very important aspect of what an SCM provides
if you go down this road, namely project history. You basically have two
choices with this "implicit save on each edit":
* force the user to supply a commit message for each and every edit
* ignore commit messages altogether

Obviously, forcing a commit message each time is the only way to get some sort of proper history to look at after it's done, but it's also such an appalling nuisance that I doubt *anyone* will actually like that, and since changesets aren't supported, you'll have "implement xniz api, commit 1 of X" messages. Cumbersome, stupid, and not very useful.

Ignoring commit messages altogether means you ignore the entire history, and the SCM then becomes a filesystem-wide "undo" cache. This could ofcourse work, but it's something akin to building a nuclear powerplant to power a single lightbulb.

-- 
Andreas Ericsson                   andreas.ericsson@op5.se
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231
david@lang.hm· Dec 7, 2007, 21:17 UTC · re: Al Boldi · lore
On Fri, 7 Dec 2007, Al Boldi wrote:
Show 40 quoted lines
> Andreas Ericsson wrote:
>> So, to get to the bottom of this, which of the following workflows is it
>> you want git to support?
>>
>> ### WORKFLOW A ###
>> edit, edit, edit
>> edit, edit, edit
>> edit, edit, edit
>> Oops I made a mistake and need to hop back to "current - 12".
>> edit, edit, edit
>> edit, edit, edit
>> publish everything, similar to just tarring up your workdir and sending
>> out ### END WORKFLOW A ###
>>
>> ### WORKFLOW B ###
>> edit, edit, edit
>> ok this looks good, I want to save a checkpoint here
>> edit, edit, edit
>> looks good again. next checkpoint
>> edit, edit, edit
>> oh crap, back to checkpoint 2
>> edit, edit, edit
>> ooh, that's better. save a checkpoint and publish those checkpoints
>> ### END WORKFLOW B ###
>
> ### WORKFLOW C ###
> for every save on a gitfs mounted dir, do an implied checkpoint, commit, or
> publish (should be adjustable), on its privately created on-the-fly
> repository.
> ### END WORKFLOW C ###
>
> For example:
>
>  echo "// last comment on this file" >> /gitfs.mounted/file
>
> should do an implied checkpoint, and make these checkpoints immediately
> visible under some checkpoint branch of the gitfs mounted dir.
>
> Note, this way the developer gets version control without even noticing, and
> works completely transparent to any kind of application.
so if you have a script that does

echo "mail header" >tmpfile echo "subject: >>tmpfile echo >>tmpfile echo "body" >>tmpfile

you want to have four seperate commits
what if you have a perl script

open outfile ">tmpfile"; print outfile "mail header\n"; print outfile "subject:\n\n"; print outfile "body\n"; close ourfile;

how many seperate commits do you think should take place?

what if $|=1 (unbuffered output, so that each print statement becomes visable to other programs immediatly)?

what if the file is changed via mmap? should each byte/word written to memory be a commit? or when the mmap is closed? or when the kernel happens to flush the page to disk?

'recording every change to a filesystem' is a very incomplete definition of a goal.

David Lang
Björn Steinbrink· Dec 7, 2007, 22:00 UTC · re: Al Boldi · lore
On 2007.12.07 13:53:11 +0300, Al Boldi wrote:
Show 40 quoted lines
> Andreas Ericsson wrote:
> > So, to get to the bottom of this, which of the following workflows is it
> > you want git to support?
> >
> > ### WORKFLOW A ###
> > edit, edit, edit
> > edit, edit, edit
> > edit, edit, edit
> > Oops I made a mistake and need to hop back to "current - 12".
> > edit, edit, edit
> > edit, edit, edit
> > publish everything, similar to just tarring up your workdir and sending
> > out ### END WORKFLOW A ###
> >
> > ### WORKFLOW B ###
> > edit, edit, edit
> > ok this looks good, I want to save a checkpoint here
> > edit, edit, edit
> > looks good again. next checkpoint
> > edit, edit, edit
> > oh crap, back to checkpoint 2
> > edit, edit, edit
> > ooh, that's better. save a checkpoint and publish those checkpoints
> > ### END WORKFLOW B ###
> 
> ### WORKFLOW C ###
> for every save on a gitfs mounted dir, do an implied checkpoint, commit, or 
> publish (should be adjustable), on its privately created on-the-fly 
> repository.
> ### END WORKFLOW C ###
> 
> For example:
> 
>   echo "// last comment on this file" >> /gitfs.mounted/file
> 
> should do an implied checkpoint, and make these checkpoints immediately 
> visible under some checkpoint branch of the gitfs mounted dir.
> 
> Note, this way the developer gets version control without even noticing, and 
> works completely transparent to any kind of application.

Ouch... That looks worse than "plain" per-file versioning. Not only do you per definition get "broken" commits if there's a change that affects two dependent files, you also get an insane amount of commits just for testing stuff, or fixing bugs.

And unless you use some kind of union-fs on top (or keep ignored files in special unversioned area in your gitfs, which seems somewhat ugly), you'll probably also have to track lots of files in the working directory that are generated, unless you want to re-generate them after each reboot. And that leads to even more absolutely useless revisions.

Just thinking of my vim .swp files (which I definitely don't want to loose on a crash/power outtage/pkill -9 .<ENTER> dammit) makes me scream because of the gazillion of commits they will produce (and no, I don't want them in some special out of tree directory).

Plus, I have vim setup to _replace_ files on write, so that I can more easily use hard-linked copies with changing all copies at once _unless_ I explicitly want to, meaning that I'd get full remove/add commits, which are absolutely useless. And trying to detect such patterns (rename, then write the changed file with the old name and then delete the renamed file) is probably not worth the trouble, because you coincidently might _want_ to have just these three steps recorded when you happen to perform them manually. And if you go for heuristics, you'll complain each time you get a false-positive/negative.

That said, out of pure curiousness I came up with the attached script which just uses inotifywait to watch a directory and issue git commands on certain events. It is extremely stupid, but seems to work. And at least it hasn't got the drawbacks of a real gitfs regarding the need to have a "separate" non-versioned storage area for the working directory, because it simply uses the existing working directory wherever that might be stored. It doesn't use GIT_DIR/WORK_DIR yet, but hey, should be easy to add...

Feel free to mess with that thing, hey, maybe you even like it and extend it to match your proposed workflow even more. I for sure won't use or even extend it, so you're likely on your own there.

Side-note: Writing that script probably took less time than writing this
email and probably less time than was wasted on this topic. Makes me
want to use today's preferred "Code talks, b...s... walks" statement,
but I'll refrain from that... Just because I lack the credibility to say
that, and the script attached is quite crappy ;-)
Björn
#!/bin/bash
inotifywait -m -r --exclude ^\./\.git/.* -e close_write -e move -e create -e delete . 2>/dev/null |
while read FILE_PATH EVENT FILE_NAME
do
	FILE_NAME="$FILE_PATH$FILE_NAME"
	FILE_NAME=${FILE_NAME#./}
	# git doesn't care about directories
	if [ -d "$FILE_NAME" ]
	then
		continue
	fi
	case "$EVENT" in
		*CLOSE_WRITE*)
		ACTION=change
		;;
		*MOVED_TO*)
		ACTION=create
		;;
		*MODIFY*)
		ACTION=change
		;;
		*DELETE*)
		ACTION=delete
		;;
		*MOVED_FROM*)
		ACTION=delete
		;;
		*CREATE*)
		ACTION=create
		;;
		*)
		continue
		;;
	esac
	case $ACTION in
		create)
		git add "$FILE_NAME"
		git commit -m "$FILE_NAME created"
		;;
		delete)
		git rm --cached "$FILE_NAME"
		git commit -m "$FILE_NAME removed"
		;;
		change)
		git add "$FILE_NAME"
		git commit -m "$FILE_NAME changed"
		;;
	esac
done
Johannes Schindelin· Aug 28, 2009, 12:30 UTC · re: Björn Steinbrink · lore

inotify-commit, was Re: git guidance

Hi,
[long Cc: list culled, as they probably forgot about this thread]
On Fri, 7 Dec 2007, Björn Steinbrink wrote:
Show 18 quoted lines
> That said, out of pure curiousness I came up with the attached script 
> which just uses inotifywait to watch a directory and issue git commands 
> on certain events. It is extremely stupid, but seems to work. And at 
> least it hasn't got the drawbacks of a real gitfs regarding the need to 
> have a "separate" non-versioned storage area for the working directory, 
> because it simply uses the existing working directory wherever that 
> might be stored. It doesn't use GIT_DIR/WORK_DIR yet, but hey, should be 
> easy to add...
> 
> Feel free to mess with that thing, hey, maybe you even like it and
> extend it to match your proposed workflow even more. I for sure won't
> use or even extend it, so you're likely on your own there.
> 
> Side-note: Writing that script probably took less time than writing this
> email and probably less time than was wasted on this topic. Makes me
> want to use today's preferred "Code talks, b...s... walks" statement,
> but I'll refrain from that... Just because I lack the credibility to say
> that, and the script attached is quite crappy ;-)
I could not agree more with the statement.

As it happens, I have a very delicate setup that we tested in a test environment as much as possible, but now we have to deploy it and I want to be able to rewind very quickly to a known-good state.

So I adjusted your script a little.  It now reads like this:

-- snip -- #!/bin/sh

# Originally by Bjoern Steinbrink, simplified by Johannes Schindelin
inotifywait -m -r --exclude ^\./\.git/.* \
        -e close_write -e move -e create -e delete . 2>/dev/null |
while read FILE_PATH EVENT FILE_NAME
do
        FILE_NAME="$FILE_PATH$FILE_NAME"
        FILE_NAME=${FILE_NAME#./}
        # git doesn't care about directories
        test -d "$FILE_NAME" && continue
        case "$EVENT" in
        *MOVED_TO*|*CREATE*)
                git add "$FILE_NAME"
                git commit -m "$FILE_NAME created"
                ;;
        *CLOSE_WRITE*|*MODIFY*)
                git add "$FILE_NAME"
                git commit -m "$FILE_NAME changed"
                ;;
        *DELETE*|*MOVED_FROM*)
                git rm --cached "$FILE_NAME"
                git commit -m "$FILE_NAME removed"
                ;;
        esac
done
-- snap --
Thanks for your original script!

Ciao, Dscho

Phillip Susi· Dec 6, 2007, 21:46 UTC · re: Al Boldi · lore
Al Boldi wrote:
> When you read server, don't read it as localized; a server can be 
> distributed.  What distinguishes a server from an engine is that it has to 
> handle a multi-user use-case.  How that is implemented, locally or remotely 
> or distributed, is another issue.
And again, git handles both use cases, so what's your point?
> As explained before in this thread, replicating the git tree on the client 
> still doesn't provide the required transparency.

It has been pointed out to you that it DOES. Either that or nobody else understands your nebulous use of "transparency" so maybe you should define it like we've been asking you. Furthermore, the comment you replied to said nothing about transparency, nor did your comment it was in reply to; rather it was pointing out the fact that your statement that the git can not perform version control on the client is patently false.

Show 10 quoted lines
>> How is that different from what every SCM, including git, is doing today?
>> The user needs to tell the scm when it's time to take a snapshot of the
>> current state. Git is distributed though, so committing is usually not the
>> same as publishing. Is that lack of a single command to commit and publish
>> what's nagging you? If it's not, I completely fail to see what you're
>> getting at, unless you've only ever looked at repositories without a
>> worktree attached, or you think that git should work like an editor's
>> "undo" functionality, which would be quite insane.
> 
> You need to re-read the thread.

Perhaps you should. We have been trying to get you to explain how you think git isn't "transparent" while at the same time pointing out how we think it is. You have failed to demonstrate any evidence to back up your claims, all of which have been shown to be false.

Martin Langhoff· Dec 8, 2007, 06:33 UTC · re: Al Boldi · lore
On Dec 1, 2007 7:50 PM, Al Boldi <a1426z@gawab.com> wrote:
> Not sure what you mean by operationally transparent?  It would be transparent
> for the updating client,  and the rest of the git-users would need to wait
> for the commit from the updating client; which is ok, as this transparency
> is not meant to change the server-side git-update semantic.

I guess what he means is that when your write to the file -- from your editor -- it can't be considered a commit. During an editing session you might write a dozen times, only to commit it once you are happy (that it compiles, passes tests, etc).

Show 5 quoted lines
> Sure, you wouldn't want to change the git-engine update semantics, as that
> sits on the server and handles all users.  But what the git model is
> currently missing is a client manager.  Right now, this is being worked
> around by replicating the git tree on the client, which still doesn't
> provide the required transparency.

If you want a dumb-ish client CVS-style, you can try git-cvsserver. But the git model is definitely superior -- "replicating the tree on the client" is not a workaround but a central strategy.

Have you used git and other DSCMs much? From your writing, it sounds like you may have misunderstood how some of the principles of git work out in practice.

cheers,
m

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