merge time

merge time

[Matthew L Foster]

Sorry to bring up the time issue again [that I am perhaps still confused about] but I have been
playing around with git more and I think I can phrase my question/observation better.

>From viewing gitweb.cgi I have observed a situation where Linus creates a tag, say rc1, and then
he later merges changes but some subset of those changes/commits show up in the list in time order
as taking place _before_ the rc1 tag was made even though they were merged after. Do I describe a
real or possible phenomenon? And does this happen because the developer that made the subset of
changes in question commit them to his/her local repository in time order before the rc1 tag was
made? So an external repository had the change before the rc1 tag was made but Linus' repository
didn't? But internally git on Linus' machine knows that the gitweb.cgi displayed time order is
wrong as far as the state is concerned because each repository's index file keeps local track of
the true local state [just time isn't reconcilable], or am I missing something(s)?

Is it possible for gitweb.cgi to have a new view mode that sorts/displays the list based on merge
time for commits (the time merged into Linus' or whatever repository) so the above situation
doesn't happen? The actual time of a local commit should be the time it was merged locally not the
time it was created externally/originally, right? Where can I find the gitweb.cgi source/package?
I could maybe hack gitweb.cgi myself.

Please CC me on any replies since I am not subscribed to the list.

-Matt



       
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Re: merge time

[Jakub Narebski]

[Cc: Matthew L Foster <mfoster167@yahoo.com>, git@vger.kernel.org]

Please, word wrap lines around 70 - 76 column.

Matthew L Foster wrote:

> Sorry to bring up the time issue again [that I am perhaps still confused
> about] but I have been playing around with git more and I think I can
> phrase my question/observation better. 
> 
> From viewing gitweb.cgi I have observed a situation where Linus creates
> a tag, say rc1, and then he later merges changes but some subset of those
> changes/commits show up in the list in time order as taking place _before_
> the rc1 tag was made even though they were merged after.

Of course. The time ordering is by the time commits were _created_,
not when they were merged.

In git, you can try tu use --topo-order parameter to git-log. In gitweb,
not yet.

> Do I describe a real or possible phenomenon?

Real phenomenon.

> And does this happen because the developer that made the subset of changes
> in question commit them to his/her local repository in time order before
> the rc1 tag was made? So an external repository had the change before the
> rc1 tag was made but Linus' repository didn't?

That's correct. Well, Linus' repository might have had change, but just
not merged in, but that is just small detail.

> But internally git on Linus' machine knows that the 
> gitweb.cgi displayed time order is wrong as far as the state is concerned
> because each repository's index file keeps local track of the true local
> state [just time isn't reconcilable], or am I missing something(s)? 

Git does not know, and git proper has no utility to show for each commit
when it was merged to given branch. And that is even more complicated by
the fast-forward merges. Reflog (local matter, not displayed in gitweb,
available as "git reflog show <branch>" or "git log --show-reflog
[<branch>]" in git) keeps track of the branch tip history; it doesn't offer
information [you think] you want.

> Is it possible for gitweb.cgi to have a new view mode that sorts/displays
> the list based on merge time for commits (the time merged into Linus' or
> whatever repository) so the above situation doesn't happen?  The actual
> time of a local commit should be the time it was merged locally not the  
> time it was created externally/originally, right?

I don't think that it is possible, but you are welcome to try...

> Where can I find the gitweb.cgi source/package?
> I could maybe hack gitweb.cgi myself.

Gitweb is now in the git.git repository, in gitweb/gitweb.perl
(see also gitweb/README and gitweb/INSTALL).
 
> Please CC me on any replies since I am not subscribed to the list.

Please Cc: list.
-- 
Jakub Narebski
Warsaw, Poland
ShadeHawk on #git

Re: merge time

[Linus Torvalds]

On Sun, 29 Jul 2007, Matthew L Foster wrote:
> 
> From viewing gitweb.cgi I have observed a situation where Linus creates 
> a tag, say rc1, and then he later merges changes but some subset of 
> those changes/commits show up in the list in time order as taking place 
> _before_ the rc1 tag was made even though they were merged after.

Absolutely. This is very common indeed. It's even more common with not the 
-rc1 tag, but a release.

When I cut a full release, that "opens the floodgates" for the merge 
window, and a lot of people who have committed their changes (maybe 
weeks or *months* before) but where the changes weren't appropriate to be 
merged before the merge window, will now ask me to pull.

So you may have the situation that 2.6.22 was released, but then a few 
days later I'll merge stuff that was actually committed two weeks before 
the 2.6.22 release, but was not _in_ the release.

> Do I describe a real or possible phenomenon? And does this happen 
> because the developer that made the subset of changes in question commit 
> them to his/her local repository in time order before the rc1 tag was 
> made?

Yes. I would seriously suggest you not use "gitweb" as your way to look at 
the repository, because you'll never see all the interactions that way. 

Cloning a git repository (not necessarily the kernel, but it needs to be 
something with concurrent developement), and exploring it locally with 
"gitk" or "qgit" is a _lot_ more informative. When you see the actual 
history chains graphically, something that might look "odd" in gitweb 
(commits that look old but weren't there a few days ago) suddenly makes 
tons of sense.

> So an external repository had the change before the rc1 tag was made but 
> Linus' repository didn't? But internally git on Linus' machine knows 
> that the gitweb.cgi displayed time order is wrong as far as the state is 
> concerned because each repository's index file keeps local track of the 
> true local state [just time isn't reconcilable], or am I missing 
> something(s)?

Well, there i sno "wrong" time. There are just "different" times. The only 
thing git really tracks is not actually the time (that's purely for human 
consumption), but the *relationship* between commits. So git really very 
fundmanetally just tracks things like "commit X was the parent of commit 
Y", and the time is really immaterial.

The time, to git, is not really different from authorship: it's very 
important to track when something was done, but it's really purely 
informational, exactly the same way the _author_ is purely informational. 
It has no "meaning" for git itself.

> Is it possible for gitweb.cgi to have a new view mode that 
> sorts/displays the list based on merge time for commits (the time merged 
> into Linus' or whatever repository) so the above situation doesn't 
> happen?

The public repositories don't even know what the merge time was for me. 
That's a purely local feature, and while I can see it in my private 
repository that I actually did the merge in, I don't publish that 
information. It's incidental, and quite frankly, it's "wrong" to care: 
because "Linus' tree" is really not even supposed to be special.

		Linus

Re: merge time

[Matthew L Foster]

--- Linus Torvalds <torvalds@linux-foundation.org> wrote:

> Well, there i sno "wrong" time. There are just "different" times. The only 
> thing git really tracks is not actually the time (that's purely for human 
> consumption), but the *relationship* between commits. So git really very 
> fundmanetally just tracks things like "commit X was the parent of commit 
> Y", and the time is really immaterial.

Is it possible for git and/or gitweb to know that commits X and Y are descendents of merge C and
use the time merge C happened locally for both instead of using the time commits X and Y were
created? It seems to me changes showing up as being made long before they really were merged is a
very serious problem verification wise but if everyone is using git then perhaps it's not as bad
as I think. What happens when security bug fix Z errantly seems to be in v2.6.22 but in reality
its not?

Thanks for the responses,
-Matt



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Re: merge time

[david]

On Sun, 29 Jul 2007, Matthew L Foster wrote:

> --- Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
>> Well, there i sno "wrong" time. There are just "different" times. The only
>> thing git really tracks is not actually the time (that's purely for human
>> consumption), but the *relationship* between commits. So git really very
>> fundmanetally just tracks things like "commit X was the parent of commit
>> Y", and the time is really immaterial.
>
> Is it possible for git and/or gitweb to know that commits X and Y are descendents of merge C and
> use the time merge C happened locally for both instead of using the time commits X and Y were
> created?

git knows what's a decendent of what, but gitweb doesn't show it well. 
that's why Linus suggested you look at gitk or qgit.

by the way, you probably mean that commits X and Y are parents of merge C, 
not decendants.

but if git did what you wanted it would show every commit with the time of 
the merge, and that wouldn't help you anyway.

> It seems to me changes showing up as being made long before they really were merged is a
> very serious problem verification wise but if everyone is using git then perhaps it's not as bad
> as I think. What happens when security bug fix Z errantly seems to be in v2.6.22 but in reality
> its not?

you don't look at the dates to see if the bugfix is in 2.6.22 you look at 
the graph or ask git to tell you

remember that in git you don't have one-true-trunk of the project, you 
have a mesh of interconnected points, some of which are pointed to by tags 
that tell you that other people thought that they are particularly 
interesting.

David Lang

> Thanks for the responses,
> -Matt
>
>
>
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Re: merge time

[Linus Torvalds]

On Sun, 29 Jul 2007, Matthew L Foster wrote:
> 
> Is it possible for git and/or gitweb to know that commits X and Y are descendents of merge C and
> use the time merge C happened locally for both instead of using the time commits X and Y were
> created?

The data exists, but there is nothing to make "C" special. Or rather, the 
two "sides" of C that got merged are 100% equivalent.

You'd probably have to read a lot of old emails (from very early in the 
git process) to see the whole picture. But the fact is, in a distributed 
environment, the parents to a merge C are totally equivalent.

So thus when you talk about merge new code into an old repository (and 
giving those new commits the same date as the merge), that is actually 
technically 100% equivalent to merging the other way around, and thus 
you'd have to give all the *old* commits that new merge date too!

And yes, this does happen. It's not at all the case that I always merge 
other peoples tree: quite often other people merge _my_ tree, and the end 
result really is that they pulled in the changes _I_ had done.

[ Side note: we do actually try to avoid that, just because it makes the 
  history harder to read, and the resulting criss-cross merges, while 
  technically not a problem at all, can confuse people. But when I say 
  "try to avoid that", I mean just that: it's not a hard rule, and the 
  reverse merging _does_ happen, and there are good reasons for why it 
  happens.

  So *most* of the time, the history looks like it's me merging other 
  peoples code, but then every once in a while, the merge is done by the 
  other side. And from a pure technical standpoint, the two cases are 
  totally equivalent, and git is very fundamentally designed to *not* 
  care. ]

So there is never really any way to say that one side of a merge is 
special. The closest you can get is saying

 - the first parent is special.

   This is "see merges from the viewpoint of the merger", but as 
   mentioned, the person who actually did the merge isn't necessarily me, 
   so while this is a totally self-consistent view, it's not really the 
   view you are looking for.

   You can get some of this view by using "git log --first-parent", which 
   basically follows commits preferentially using the first parent, and 
   thus "prefers" history as seen by whoever did the merge.

or

 - the *local* repository is special (but this is a purely repository- 
   local viewpoint).

   This is what "reflogs" give you, and what "git log -g" shows. It shows 
   the history not as it pertains to parenthood, but as the tip-of-tree 
   has changed in *that* repository.

but neither of those are really "sensible" (the first one will give 
*wildly* different results if the repository is ever "switched around" 
because it's not merged by a single person, and the second one is a purely 
local thing and has no meaning for anybody else.

The fact is, distributed history isn't one-dimensional. You *cannot* 
linearize it as some one-dimensional time. Impossible. Any system that 
tries is broken. Fundamentally.

		Linus

Re: merge time

[Matthew L Foster]

--- Linus Torvalds <torvalds@linux-foundation.org> wrote:

> The fact is, distributed history isn't one-dimensional. You *cannot* 
> linearize it as some one-dimensional time. Impossible. Any system that 
> tries is broken. 

I don't want distributed history, I want what local time changes were merged locally. That is why
I described a separate view for this feature, this feature request is not meant to replace how
time is currently not being used. :)

-Matt


       
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Re: merge time

[Linus Torvalds]

On Sun, 29 Jul 2007, Matthew L Foster wrote:
> 
> --- Linus Torvalds <torvalds@linux-foundation.org> wrote:
> 
> > The fact is, distributed history isn't one-dimensional. You *cannot* 
> > linearize it as some one-dimensional time. Impossible. Any system that 
> > tries is broken. 
> 
> I don't want distributed history, I want what local time changes were 
> merged locally.

The point is, there is no "locally".

Do you mean locally on my machine? That's actually *different* from the 
locally on the public machines, and no, I wouldn't give you that 
information anyway (since that information would include the mistakes that 
I fixed up ;)

And in fact, even on the public machines, the "locally" would be different 
depending on things like mirroring delays, although that is currently 
hidden by the fact that kernel.org uses rsync for mirroring rather than 
using git natively.

So in theory, we could pick one particular public kernel.org machine, and 
use the times as _that_ machine sees it, but the fact is, that isn't how 
git works. No normal git command will ever show you such a senseless 
ordering.

I suspect that the closest you could get to what you want would be to 
actually run git-cvsserver on kernel.org to export the git data as "CVS" 
data, and then you could use a CVS client that gets a linearized model of 
history. That is, afaik, the only way to give you what you want.

And quite frankly, I'd never ask the kernel.org maintainers to do 
something that perverse. You could ask them, and maybe they would do so 
out of some really perverse self-destructive death-wish, but quite 
frankly, you'd probably be better off setting up such a git->CVS gateway 
on some local machine yourself.

			Linus

Re: merge time

[Linus Torvalds]

On Sun, 29 Jul 2007, Linus Torvalds wrote:
>
> So in theory, we could pick one particular public kernel.org machine, and 
> use the times as _that_ machine sees it, but the fact is, that isn't how 
> git works. No normal git command will ever show you such a senseless 
> ordering.

So to be constructive, and just tell you what the *sensible* ordering is:

 - get a kernel git clone

 - do "git pull" to update it.

 - do

	gitk ORIG_HEAD..

   to show what the new stuff is after each update, or do something like

	gitk v2.6.23-rc1..

  to show what is new after -rc1 (or "gitk @{2.days.ago}.." to see what 
  is new in _your_ tree in the last two days or whatever).

No commit dates anywhere. Just commit relationships and your *local* views 
of time.

(Sure, gitk will show you the commit dates too, but they aren't important, 
since they have no meaning as to whether a commit got merged into 
2.6.23-rc1 or not).

		Linus

Re: merge time

[Matthew L Foster]

--- Linus Torvalds <torvalds@linux-foundation.org> wrote:

> (Sure, gitk will show you the commit dates too, but they aren't important, 
> since they have no meaning as to whether a commit got merged into 
> 2.6.23-rc1 or not).





       
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Re: merge time

[Sean]

On Sun, 29 Jul 2007 20:16:01 -0700 (PDT)
Linus Torvalds <torvalds@linux-foundation.org> wrote:


> 	gitk v2.6.23-rc1..
> 
>   to show what is new after -rc1 (or "gitk @{2.days.ago}.." to see what 
>   is new in _your_ tree in the last two days or whatever).

It sounds like that would be the proper way to address the issue
within Gitweb as well.  Assuming the issue is users wanting to
see changes since a specific release, offering a "Commits since tag"
option or some such should resolve it.

Sean

Re: merge time

[Matthew L Foster]

--- Linus Torvalds <torvalds@linux-foundation.org> wrote:
 
> The point is, there is no "locally".
> 
> Do you mean locally on my machine? That's actually *different* from the 
> locally on the public machines, and no, I wouldn't give you that 
> information anyway (since that information would include the mistakes that 
> I fixed up ;)

Ok that explains it. How about locally on gitX.kernel.org [would have to be real git repository]?
I'd want gitweb.cgi running on my local repository to use the local time of local merges to ensure
the problem I described at the start of this thread doesn't happen. Git reset --hard can be used
to fix mistakes and that wouldn't show? 

> And in fact, even on the public machines, the "locally" would be different 
> depending on things like mirroring delays

Yes, it should be different, everyone's local commit/merge order is not the same.

> So in theory, we could pick one particular public kernel.org machine, and 
> use the times as _that_ machine sees it, but the fact is, that isn't how 
> git works. No normal git command will ever show you such a senseless 
> ordering.

Is local commit order really senseless? Using local commit order and/or the local time of local
merges would solve the problem I mentioned in the start of this thread? I don't think this info
has to be exported to CVS, a web interface to git and/or git itself should be able to tell us what
local time order and/or what local commit order merges were made in.

-Matt



       
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Re: merge time

[Steffen Prohaska]

On Jul 30, 2007, at 4:29 AM, Linus Torvalds wrote:

> So there is never really any way to say that one side of a merge is
> special. The closest you can get is saying
>
>  - the first parent is special.
>
>    This is "see merges from the viewpoint of the merger", but as
>    mentioned, the person who actually did the merge isn't  
> necessarily me,
>    so while this is a totally self-consistent view, it's not really  
> the
>    view you are looking for.
>
>    You can get some of this view by using "git log --first-parent",  
> which
>    basically follows commits preferentially using the first parent,  
> and
>    thus "prefers" history as seen by whoever did the merge.

In general the first parent is not special, agreed. But could one
deliberately built a history by following certain rules that make
the first parent _always_ a special one?

I think of a quite simple example. Topic branches are always
branched off the master, and later merged back. The master, which
is the branch an official release is created from, must always be
the first parent during a merge. It doesn't matter who does the
merges or who does the releases, as long as he follows the rule
to start from the last release point and merge in all changes in
the appropriate way, such that the first parent rule is followed.

Here are two applications that I think would be interesting:

1) The kernel history. If you went from a current release back
along the first parents you'd see the changes that entered the
official kernel sorted backwards in time. I believe the history of
the kernel is already an approximation of this rule. But maybe I'm
wrong.

2) Developing using topic branches. You start topic branches and
start developing new features. Only later you fix problems on all
supported platforms, polish and review the changes. Not every
commit on the topic branch has the same quality, e.g. the early
commits may not even compile on all supported platforms. But the
tip of the topic branch passes all required tests. After a merge
of the topic branch to a stable branch it would be nice to
distinguish the stable history from the less polished commits on
the topic branch. I think this could be achieved if the first
parent always is linked to a stable commit.

I'm sure some will propose that instead of (2) I should rewrite a
topic branch such that every single commit passes all quality
requirements. But I strongly believe it is a viable choice not to
do so. It may just be too much work and often it's sufficient and
easier to polish the tip of a topic branch.

Fast-forward merges would break both of the scenarios. But would
they be possible without fast-forward merges?

Would it be possible to ensure that all commits along the
first-parent-path have 'release' quality and all release tags are
located along this path? What would be the right rules to achieve
this objective?

	Steffen

Re: merge time

[Junio C Hamano]

This is an old topic rehashed from time to time.  The last time
was March this year if I recall correctly.

    http://thread.gmane.org/gmane.comp.version-control.git/41931/focus=41983
 
I tend to agree that it would make sense to allow something like:

    $ git merge --no-fast-forward -m 'Merge topic XYZ' xyz

but at the same time Linus is pretty clear that he would not use
that for his kernel merges, so even if we add that feature,
gitweb at k.org that shows linux-2.6 history would not see it.

Re: merge time

[Steffen Prohaska]

On Jul 30, 2007, at 8:48 AM, Junio C Hamano wrote:

> I tend to agree that it would make sense to allow something like:
>
>     $ git merge --no-fast-forward -m 'Merge topic XYZ' xyz

Another option could be to force a commit before the merge, even
if there are no changes to commit, something like

     $ git commit --force -m 'MARK'

[to my knowledge, --force or similar is not yet available]

	Steffen

Re: merge time

[Shawn O. Pearce]

Steffen Prohaska <prohaska@zib.de> wrote:
> Another option could be to force a commit before the merge, even
> if there are no changes to commit, something like
> 
>     $ git commit --force -m 'MARK'
> 
> [to my knowledge, --force or similar is not yet available]

git-force-commit:

  git config --global alias.force-commit \
  '! git update-ref HEAD $(echo MARK | git commit-tree HEAD -p HEAD)'

But you didn't hear it from me.  ;-)

Yes, I've actually done this once in a while.  But only to create
some temporary throw-away state that I need for some diff operation
or whatnot.  Usually because I make it in one repository, but want
to fetch it into another and fetch likes moving refs to commits
better than refs to trees.  Oh, and I'm usually passing in more
than one -p, and usually not HEAD as the tree.  But whatever.

-- 
Shawn.

Re: merge time

[Steffen Prohaska]

On Jul 30, 2007, at 9:49 AM, Shawn O. Pearce wrote:

> git-force-commit:
>
>   git config --global alias.force-commit \
>   '! git update-ref HEAD $(echo MARK | git commit-tree HEAD -p HEAD)'

I needed to slightly modify it

     git config --global alias.force-commit \
     '! git update-ref HEAD $(echo MARK | git commit-tree $(git cat- 
file commit HEAD | grep ^tree | cut -b 6-) -p HEAD)'

> But you didn't hear it from me.  ;-)

I'll tell no-one ;)

	Steffen

Re: merge time

[Jeff King]

On Mon, Jul 30, 2007 at 10:09:16AM +0200, Steffen Prohaska wrote:

> I needed to slightly modify it
>
>     git config --global alias.force-commit \
>     '! git update-ref HEAD $(echo MARK | git commit-tree $(git cat-file 
> commit HEAD | grep ^tree | cut -b 6-) -p HEAD)'

How about "git commit-tree HEAD^{tree} -p HEAD"?

But I think making a "fake" commit to force non-fast-forward is the
wrong thing. You really want to make your "extra" commit be the merge
that wouldn't have happened (which unfortunately is not as simple as
just creating a commit by hand, since you have to actually _do_ the
merge to get the tree).

-Peff

Re: merge time

[Junio C Hamano]

Jeff King <peff@peff.net> writes:

> But I think making a "fake" commit to force non-fast-forward is the
> wrong thing. You really want to make your "extra" commit be the merge
> that wouldn't have happened (which unfortunately is not as simple as
> just creating a commit by hand, since you have to actually _do_ the
> merge to get the tree).

I do agree that if you really want to create a commit instead of
allowing a fast forward, you really should create a proper merge
commit.

But it is not hard.  If it is a fast forward in reality but you
are marking it as a real merge by creating a merge commit, then:

 - The tree is obviously the merged branch that is a fast
   forward of your old HEAD;

 - The first parent of the resulting merge is your old HEAD; and

 - The second parent of the resulting merge is the merged
   branch.

So:

	git merge --no-fast-forward other

when other is a fast forward of HEAD would do:

	git commit-tree other^{tree} -p HEAD -p other

Re: merge time

[Jeff King]

On Mon, Jul 30, 2007 at 01:24:43AM -0700, Junio C Hamano wrote:

> But it is not hard.  If it is a fast forward in reality but you
> are marking it as a real merge by creating a merge commit, then:

Of course, I was not thinking right. I was considering the difficulty of
invoking the merge machinery, but of course by definition for a
fast-forward you don't have to.

> when other is a fast forward of HEAD would do:
> 
> 	git commit-tree other^{tree} -p HEAD -p other

Yes, that makes sense.

-Peff

Re: merge time

[Steffen Prohaska]

On Jul 30, 2007, at 10:14 AM, Jeff King wrote:

>
> How about "git commit-tree HEAD^{tree} -p HEAD"?

Thanks, I wasn't aware of this syntax.

> But I think making a "fake" commit to force non-fast-forward is the
> wrong thing. You really want to make your "extra" commit be the merge
> that wouldn't have happened (which unfortunately is not as simple as
> just creating a commit by hand, since you have to actually _do_ the
> merge to get the tree).

I agree. But I think except for being 'fake' there shouldn't be any
problems with the extra commit.

	Steffen

Re: merge time

[Jeff King]

On Mon, Jul 30, 2007 at 10:25:25AM +0200, Steffen Prohaska wrote:

> I agree. But I think except for being 'fake' there shouldn't be any
> problems with the extra commit.

Problems, no. But it will look ugly when browsing history. :)

-Peff

Re: merge time

[david]

On Mon, 30 Jul 2007, Jeff King wrote:

> On Mon, Jul 30, 2007 at 10:25:25AM +0200, Steffen Prohaska wrote:
>
>> I agree. But I think except for being 'fake' there shouldn't be any
>> problems with the extra commit.
>
> Problems, no. But it will look ugly when browsing history. :)

yes, but this entire thread was an attempt to avoid browsing the history 
and instead figure out the relationships between commits by dates. so the 
people wanting this don't care how ugly it makes the history (but since 
they want to do this in other people's repositories this won't work for 
them either)

David Lang

Re: merge time

[Jeff King]

On Mon, Jul 30, 2007 at 01:34:55AM -0700, david@lang.hm wrote:

> yes, but this entire thread was an attempt to avoid browsing the history and 
> instead figure out the relationships between commits by dates. so the people 
> wanting this don't care how ugly it makes the history (but since they want 
> to do this in other people's repositories this won't work for them either)

I think we drifted a bit from that with Steffen's original message...

If you followed a strict policy of always merging topics to a "base"
branch as your first parent, then never allowing fast forwards should
allow a very easy-to-read history in gitk. The left-most line of commits
would simply be a record of topics getting merged in, and would never
contain any "non-base" commits.

-Peff

Re: merge time

[Linus Torvalds]

On Mon, 30 Jul 2007, Jeff King wrote:
> 
> If you followed a strict policy of always merging topics to a "base"
> branch as your first parent, then never allowing fast forwards should
> allow a very easy-to-read history in gitk.

Only if only *one* person ever does any merges.

Immediately when you have other people merging code, you're now back in 
the same boat.

This is why I personally think the whole policy of "no fast forward" is 
totally broken. It's only usable in a non-distributed environment, where 
there is one central person who does everythng (a so-called "star 
topology").

			Linus

Re: merge time

[Steffen Prohaska]

On Jul 30, 2007, at 7:42 PM, Linus Torvalds wrote:

> On Mon, 30 Jul 2007, Jeff King wrote:
>>
>> If you followed a strict policy of always merging topics to a "base"
>> branch as your first parent, then never allowing fast forwards should
>> allow a very easy-to-read history in gitk.
>
> Only if only *one* person ever does any merges.
>
> Immediately when you have other people merging code, you're now  
> back in
> the same boat.
>
> This is why I personally think the whole policy of "no fast  
> forward" is
> totally broken. It's only usable in a non-distributed environment,  
> where
> there is one central person who does everything (a so-called "star
> topology").

I think no fast forward merges can always provide useful information.

Public releases are often created from a public, linear branch that
is not arbitrarily jumping around. Even if more than one person creates
such releases there must be some agreement upon the responsibility for
the release and thus for the branch the releases are created from.

If all agreed to merge topics following the "no fast forward" policy and
to use the release branch as a first parent, the commits along the first
parents would document how commits came into the release branch. Non  
fast
forward merges would always document that a series of commits was added
to the release branch at once at the (local time) of the merge commit.

If fast forwards are allowed it depends on whether the release branch  
can
be fast-forwarded over a series of commits on a topic branch or not.
In case of fast-forward, the history makes you believe each of the  
commits
of the topic branch entered the release branch separately. It hides that
they were all merged at once.

I think, avoiding fast forwards may also be used to document a different
level of quality required from commits to a topic branch and from  
commits
to the release branch. A the time of the merge the tip of a topic branch
must fulfill all quality requirements, for example compile on all  
platforms
and pass all tests. But this need not be the case for every single  
commit
on the topic branch. If you avoid fast forwards you still get a chain of
commits along the first parent that would fulfill your quality  
requirements.
If you allowed a fast forward over a low quality topic branch your chain
might be broken and you can't be sure, which commits will have high  
quality
and which one have a lower quality.

You may argue that this is all crap because every single commit  
should be
of highest quality, but I think this is unrealistic. Especially if  
more than
one person is jointly working on a topic branch and less experienced and
more experienced developers work together. It may also be rational to  
first
get the basic functionality right and later polish work for several  
platforms
and usage scenarios.

Obviously other techniques, like rewriting a topic branch to a  
perfect commit
series may be used as well. But from my understanding this may be  
hard if more
than a single person is involved. You could also squash the complete  
topic
branch into a single commit but then valuable history might get lost.

I don't see why what I have in mind would break if other people are  
merging
code, too. They may or may not follow my local rules. But at the time of
merging their changes, I can enforce my local quality policy and  
document
this by create a merge commit.

This could even be applied recursively. You could start to do a  
couple of
merges but only thoroughly test the final result of the last merge.  
You could
then enforce a link between the last very stable commit before you  
did all the
merges and the very well tested result after the final merge by  
enforcing a
"no fast forward" merge.

I'm not quite sure if such a history would be useful in the long term or
may just become to complex. I'm also not sure if the artificial links  
would
cause any trouble. I'm wondering, for example, if there are any cases  
in which
the additional links would make branching and merging harder.

	Steffen

Re: merge time

[david]

main trunk is at commit X

developer clones Y and adds a patch to it

the merge from Y's tree to the main trunk is a fast-forward

David Lang

On Tue, 31 Jul 2007, Steffen Prohaska wrote:

> Date: Tue, 31 Jul 2007 20:06:24 +0200
> From: Steffen Prohaska <prohaska@zib.de>
> To: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Jeff King <peff@peff.net>, david@lang.hm,
>     Shawn O. Pearce <spearce@spearce.org>, Junio C Hamano <gitster@pobox.com>,
>     Matthew L Foster <mfoster167@yahoo.com>, git@vger.kernel.org
> Subject: Re: merge time
> 
>
> On Jul 30, 2007, at 7:42 PM, Linus Torvalds wrote:
>
>> On Mon, 30 Jul 2007, Jeff King wrote:
>> > 
>> > If you followed a strict policy of always merging topics to a "base"
>> > branch as your first parent, then never allowing fast forwards should
>> > allow a very easy-to-read history in gitk.
>> 
>> Only if only *one* person ever does any merges.
>> 
>> Immediately when you have other people merging code, you're now back in
>> the same boat.
>> 
>> This is why I personally think the whole policy of "no fast forward" is
>> totally broken. It's only usable in a non-distributed environment, where
>> there is one central person who does everything (a so-called "star
>> topology").
>
> I think no fast forward merges can always provide useful information.
>
> Public releases are often created from a public, linear branch that
> is not arbitrarily jumping around. Even if more than one person creates
> such releases there must be some agreement upon the responsibility for
> the release and thus for the branch the releases are created from.
>
> If all agreed to merge topics following the "no fast forward" policy and
> to use the release branch as a first parent, the commits along the first
> parents would document how commits came into the release branch. Non fast
> forward merges would always document that a series of commits was added
> to the release branch at once at the (local time) of the merge commit.
>
> If fast forwards are allowed it depends on whether the release branch can
> be fast-forwarded over a series of commits on a topic branch or not.
> In case of fast-forward, the history makes you believe each of the commits
> of the topic branch entered the release branch separately. It hides that
> they were all merged at once.
>
> I think, avoiding fast forwards may also be used to document a different
> level of quality required from commits to a topic branch and from commits
> to the release branch. A the time of the merge the tip of a topic branch
> must fulfill all quality requirements, for example compile on all platforms
> and pass all tests. But this need not be the case for every single commit
> on the topic branch. If you avoid fast forwards you still get a chain of
> commits along the first parent that would fulfill your quality requirements.
> If you allowed a fast forward over a low quality topic branch your chain
> might be broken and you can't be sure, which commits will have high quality
> and which one have a lower quality.
>
> You may argue that this is all crap because every single commit should be
> of highest quality, but I think this is unrealistic. Especially if more than
> one person is jointly working on a topic branch and less experienced and
> more experienced developers work together. It may also be rational to first
> get the basic functionality right and later polish work for several platforms
> and usage scenarios.
>
> Obviously other techniques, like rewriting a topic branch to a perfect commit
> series may be used as well. But from my understanding this may be hard if 
> more
> than a single person is involved. You could also squash the complete topic
> branch into a single commit but then valuable history might get lost.
>
> I don't see why what I have in mind would break if other people are merging
> code, too. They may or may not follow my local rules. But at the time of
> merging their changes, I can enforce my local quality policy and document
> this by create a merge commit.
>
> This could even be applied recursively. You could start to do a couple of
> merges but only thoroughly test the final result of the last merge. You could
> then enforce a link between the last very stable commit before you did all 
> the
> merges and the very well tested result after the final merge by enforcing a
> "no fast forward" merge.
>
> I'm not quite sure if such a history would be useful in the long term or
> may just become to complex. I'm also not sure if the artificial links would
> cause any trouble. I'm wondering, for example, if there are any cases in 
> which
> the additional links would make branching and merging harder.
>
> 	Steffen
>
>

Re: merge time

[Rogan Dawes]

Matthew L Foster wrote:
> Sorry to bring up the time issue again [that I am perhaps still confused about] but I have been
> playing around with git more and I think I can phrase my question/observation better.
> 
> From viewing gitweb.cgi I have observed a situation where Linus creates a tag, say rc1, and then
> he later merges changes but some subset of those changes/commits show up in the list in time order
> as taking place _before_ the rc1 tag was made even though they were merged after. Do I describe a
> real or possible phenomenon? And does this happen because the developer that made the subset of
> changes in question commit them to his/her local repository in time order before the rc1 tag was
> made? So an external repository had the change before the rc1 tag was made but Linus' repository
> didn't? But internally git on Linus' machine knows that the gitweb.cgi displayed time order is
> wrong as far as the state is concerned because each repository's index file keeps local track of
> the true local state [just time isn't reconcilable], or am I missing something(s)?
> 
> Is it possible for gitweb.cgi to have a new view mode that sorts/displays the list based on merge
> time for commits (the time merged into Linus' or whatever repository) so the above situation
> doesn't happen? The actual time of a local commit should be the time it was merged locally not the
> time it was created externally/originally, right? Where can I find the gitweb.cgi source/package?
> I could maybe hack gitweb.cgi myself.
> 
> Please CC me on any replies since I am not subscribed to the list.
> 
> -Matt

The last time this topic came up, folks either created (or pointed to) 
reflogs as a way to determine the changes to the local state of a repo.

i.e. by checking the reflog for a ref, you could say that that ref was 
changed from v2.6.20 to v2.6.21 at such and such date and time.

That would allow you to determine what commits were available via that 
ref at a particular time, regardless of the actual commit dates.

To the best of my knowledge, though, reflogs are not enabled by default 
on bare repos, and gitweb makes no use of the reflogs anyway.

Rogan

Re: merge time

[Matthew L Foster]

Maybe I am the only one that thinks the web interface should be just as feature rich as the
command line interface? 

-Matt



       
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Re: merge time

[Johannes Schindelin]

Hi,

On Mon, 30 Jul 2007, Matthew L Foster wrote:

> Maybe I am the only one that thinks the web interface should be just as 
> feature rich as the command line interface?

*lol*  I would be _nice_.  But frankly, how do you want to get the power 
of the command line into a website, _without_ reproducing a command line?  
I can _script_ the command line, for example.

Ciao,
Dscho

Re: merge time

[Matthew L Foster]

--- Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:
 
> > Maybe I am the only one that thinks the web interface should be just as 
> > feature rich as the command line interface?
> 
> *lol*  I would be _nice_.  But frankly, how do you want to get the power 
> of the command line into a website, _without_ reproducing a command line?  
> I can _script_ the command line, for example.

Creating a webified command line is a perfectly fine solution towards making gitweb.cgi as full
featured as git is.

-Matt


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Re: merge time

[Rogan Dawes]

Matthew L Foster wrote:
> Maybe I am the only one that thinks the web interface should be just as feature rich as the
> command line interface? 
> 
> -Matt
> 

Well, having said that "Use reflogs" was the general response, I don't 
think that anyone ever really followed through and made it a readily 
accessible feature, even on the command line.

That is, the reflogs are readily accessible, but noone made it possible 
to link them to the commits in such a way that the dates/times change as 
you seem to desire.

Of course, you can do things like:

$ git show HEAD@{2.days.ago}

to see what HEAD looked like 2 days ago, but you can't do things like 
get gitk to show you that this tag only appeared in your repo 2 days ago.

(Keep in mind, of course, that reflogs are referring to YOUR local copy 
of the git repo, not what HEAD was on the server that you cloned from.)

And also keep in mind that on the command line you can invoke a lot of 
"plumbing commands" that you certainly wouldn't expect to be exposed in 
a web interface.

Rogan

Re: merge time

[Matthew L Foster]

--- Rogan Dawes <lists@dawes.za.net> wrote:

> And also keep in mind that on the command line you can invoke a lot of 
> "plumbing commands" that you certainly wouldn't expect to be exposed in 
> a web interface.

If the web interface requires logins over https why can't plumbing commands be exposed to the web?
Though I agree not everything needs to be webified. What I envision is a wikipedia style interface
front end with git remaining the backend so you can more easily browse the file system and see
history and diff the way you can on Wikipedia. But that idea is very separate from my concern that
right now gitweb.cgi effectively has a bug in it because it sorts using external/superset commit
order/time rather than local commit order which causes changes to appear as if they were made 
before they were really merged locally.

-Matt



       
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Re: merge time

[david]

On Mon, 30 Jul 2007, Matthew L Foster wrote:

> --- Rogan Dawes <lists@dawes.za.net> wrote:
>
>> And also keep in mind that on the command line you can invoke a lot of
>> "plumbing commands" that you certainly wouldn't expect to be exposed in
>> a web interface.
>
> If the web interface requires logins over https why can't plumbing commands be exposed to the web?
> Though I agree not everything needs to be webified. What I envision is a wikipedia style interface
> front end with git remaining the backend so you can more easily browse the file system and see
> history and diff the way you can on Wikipedia. But that idea is very separate from my concern that
> right now gitweb.cgi effectively has a bug in it because it sorts using external/superset commit
> order/time rather than local commit order which causes changes to appear as if they were made
> before they were really merged locally.

what you are asking for would be a very useful piece of software, but 
that's very different from the current gitweb. you are fileing a bug about 
the software doing what it was designed to do. yes, it could be done 
differently. yes, that would be useful. but the software to do so is 
mostly a new product, not a simple tweak to the existing gitweb software.

right now gitweb isn't designed for figuring out what was merged when, 
it's just for retreiving specific versions.

if someone really wanted to do this, the right answer may be to take the 
concept of gitk and webify it (think SVG for the graphics and AJAX 
interfaces to retreive the info as needed). I think this would be a very 
useful tool, but it would be a lot of work to implement.

but without the graph showing the commits and how they are related to each 
other, you really are crippled in your ability to figure out how things 
are related to each other. Date order just doesn't cut it.

David Lang

Re: merge time

[Jakub Narebski]

david@lang.hm wrote:

> if someone really wanted to do this, the right answer may be to take the 
> concept of gitk and webify it (think SVG for the graphics and AJAX 
> interfaces to retreive the info as needed). I think this would be a very 
> useful tool, but it would be a lot of work to implement.
> 
> but without the graph showing the commits and how they are related to each 
> other, you really are crippled in your ability to figure out how things 
> are related to each other. Date order just doesn't cut it.

By the way, gitweb at repo.or.cz has graphical log (a la gitk) using
git-browser by Arteem Khodush, which uses JavaScript library for graphics
(creating lines box by box) and a bit of AJAX-ism.

I was thinking about using "template" PNG with transparency and colored
boxes to have lighter than git-browser graphical history in gitweb, but...

By the way, you can try to add --topo-order support to gitweb, although I'm
not sure if it would do what you want.
-- 
Jakub Narebski
Warsaw, Poland
ShadeHawk on #git

Re: merge time

[Matthew L Foster]

> but if git did what you wanted it would show every commit with the time of 
> the merge, and that wouldn't help you anyway.
 
Actually that is exactly what I want. I want to know what local time change X and Y (and all
changes) were merged locally.

-Matt



       
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Re: merge time

[Linus Torvalds]

On Sun, 29 Jul 2007, Matthew L Foster wrote:
> 
> > but if git did what you wanted it would show every commit with the time of 
> > the merge, and that wouldn't help you anyway.
>  
> Actually that is exactly what I want. I want to know what local time change X and Y (and all
> changes) were merged locally.

You misunderstand. It would do so both for the newly merged commits *and* 
for the old commits. Because _you_ think the "new" commits got merged, but 
it's logically exactly equivalent to saying that the *old* commits got 
merged.

So now *every* single commit would get the timestamp of the merge.

See? It would be pointless.

			Linus

Re: merge time

[Matthew L Foster]

--- Linus Torvalds <torvalds@linux-foundation.org> wrote:

> You misunderstand. It would do so both for the newly merged commits *and* 
> for the old commits. Because _you_ think the "new" commits got merged, but 
> it's logically exactly equivalent to saying that the *old* commits got 
> merged.
> 
> So now *every* single commit would get the timestamp of the merge.
> 
> See? It would be pointless.

Ok maybe I am still confused. If a repository is in state A and a merge happens changing it to
state B we can give the changes that got us to B the timestamp of the merge? Since the changes
that got us from A to B were all merged locally at the same time they should be given the same
timestamp, right? Please explain more about how changes/commits in state A would also be given the
timestamp of the merge?

When I say local time I also really mean local commit order as both should be interchangeable
unless you widly misset/change your local clock. Git/gitweb could have an option to sort/display
based on local commit order and maybe have check for if local time order is out of sync with local
commit order.

-Matt


       
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Re: merge time

[david]

On Sun, 29 Jul 2007, Matthew L Foster wrote:

> --- Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
>> You misunderstand. It would do so both for the newly merged commits *and*
>> for the old commits. Because _you_ think the "new" commits got merged, but
>> it's logically exactly equivalent to saying that the *old* commits got
>> merged.
>>
>> So now *every* single commit would get the timestamp of the merge.
>>
>> See? It would be pointless.
>
> Ok maybe I am still confused. If a repository is in state A and a merge happens changing it to
> state B we can give the changes that got us to B the timestamp of the merge? Since the changes
> that got us from A to B were all merged locally at the same time they should be given the same
> timestamp, right? Please explain more about how changes/commits in state A would also be given the
> timestamp of the merge?
>
> When I say local time I also really mean local commit order as both should be interchangeable
> unless you widly misset/change your local clock. Git/gitweb could have an option to sort/display
> based on local commit order and maybe have check for if local time order is out of sync with local
> commit order.

one feature of git (and I think of truely distributed change management 
systems)

say you have tree A and I have tree B

if you clone your tree and merge from mine, and I clone my tree and merge 
from yours, the result of both merges _must_ be the same there will be 
trouble when we both try and merge with tree C later on.

another thing is that a given commit cannot be changed once it's created 
(if it was changed it wouldn't have the same sha1 value) so you can't just 
go around changeing dates on commits that took place elsewhere.

David Lang

Re: merge time

[Matthew L Foster]

--- david@lang.hm wrote:

> if you clone your tree and merge from mine, and I clone my tree and merge 
> from yours, the result of both merges _must_ be the same there will be 
> trouble when we both try and merge with tree C later on.
> 
> another thing is that a given commit cannot be changed once it's created 
> (if it was changed it wouldn't have the same sha1 value) so you can't just 
> go around changeing dates on commits that took place elsewhere.

Local commit order is stored locally right? From looking at gitweb on kernel.org it seems all the
info is already there, a merge has a list of commits in that merge and they should be displayed in
local commit order rather than external creation time order.

-Matt



       
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Re: merge time

[david]

On Mon, 30 Jul 2007, Matthew L Foster wrote:

> --- david@lang.hm wrote:
>
>> if you clone your tree and merge from mine, and I clone my tree and merge
>> from yours, the result of both merges _must_ be the same there will be
>> trouble when we both try and merge with tree C later on.
>>
>> another thing is that a given commit cannot be changed once it's created
>> (if it was changed it wouldn't have the same sha1 value) so you can't just
>> go around changeing dates on commits that took place elsewhere.
>
> Local commit order is stored locally right?

not normally. you could enable reflogs and then mine through the reflogs 
to find the info, but it's not stored in any easy to access fashion.

David Lang

> From looking at gitweb on kernel.org it seems all the
> info is already there, a merge has a list of commits in that merge and they should be displayed in
> local commit order rather than external creation time order.
>
> -Matt
>
>
>
>
> ____________________________________________________________________________________Ready for the edge of your seat?
> Check out tonight's top picks on Yahoo! TV.
> http://tv.yahoo.com/
>

Re: merge time

[Matthew L Foster]

--- david@lang.hm wrote:

> On Mon, 30 Jul 2007, Matthew L Foster wrote:
> > Local commit order is stored locally right?
> 
> not normally. you could enable reflogs and then mine through the reflogs 
> to find the info, but it's not stored in any easy to access fashion.

Local merge order can be extracted from git? 

-Matt


       
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Re: merge time

[david]

On Mon, 30 Jul 2007, Matthew L Foster wrote:

> --- david@lang.hm wrote:
>
>> On Mon, 30 Jul 2007, Matthew L Foster wrote:
>>> Local commit order is stored locally right?
>>
>> not normally. you could enable reflogs and then mine through the reflogs
>> to find the info, but it's not stored in any easy to access fashion.
>
> Local merge order can be extracted from git?

if you have reflogs enabled on your copy of the git repository then you 
can look at when things were merged into your copy.

David Lang

Re: merge time

[Robin Rosenberg]

måndag 30 juli 2007 skrev Matthew L Foster:
> 
> --- david@lang.hm wrote:
> 
> > On Mon, 30 Jul 2007, Matthew L Foster wrote:
> > > Local commit order is stored locally right?
> > 
> > not normally. you could enable reflogs and then mine through the reflogs 
> > to find the info, but it's not stored in any easy to access fashion.
> 
> Local merge order can be extracted from git? 

Well.. depending on what your definition of merge. Yes, probably.

I dislike the term "merge" here, since no merges has to be involved, unless you
include any pulled commit into the terms. Normally a merge is a commit with
two or more parents. Fast forward merges are indistinguishable from normal 
commits.

That aside, you *can* (usually) figure the time when a commit entered the repository by examining the
reflog if the set of branches are reasonably stable The reflog gives the local time when a head
was modified (old and new commit) so from there you can usually go backwards. *But* that road is
full of pot holes. The reflog cannot per se tell when a commit entered the local repo, it can
tell when it came into view as seen from a particular head. Looking from different heads may
(will) give you different times. If the head that was used to pull the commit into the repo is
deleted you will not be able to tell when the commit entered the repo, nor will you be able to
tell whether you can tell that or not, since the reflog for that head is gone. 

The reflog doesn't list all commits, just changes to the head and it isn't necessarily linear either, ie.
it may change backward in "time" forward or even to a completely separate set of commits.

The reflog is text-only: .git/logs/<ref-name>, e.g. .git/logs/refs/heads/master so you can see for
yourself.

-- robin