timestamps not git-cloned

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timestamps not git-cloned

jidanni
Gentlemen, it's my first git-clone,
$ git-clone git://git.debian.org/git/pkg-fso/files.git
and I'm disappointed to find the timestamps of the files created are
all now and not the date of last edit. At least mention something
about this on the git-clone man page.
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Re: timestamps not git-cloned

devnull
Hi,

On Fri, Nov 28, 2008 at 7:54 AM,  <[hidden email]> wrote:
> Gentlemen, it's my first git-clone,
> $ git-clone git://git.debian.org/git/pkg-fso/files.git
> and I'm disappointed to find the timestamps of the files created are
> all now and not the date of last edit. At least mention something
> about this on the git-clone man page.

I do not think there is an VCS that records timestamps. Only file
contents are tracked. Also, if you clone from systems across time
zones, what time do you expect to set on the files. IMO, it is not
practical to track timestamps.
 Are you concerned of 'make' doing a complete build when you switch
branches? I guess it makes sense only in that scenario. I wish 'make'
had some feature to track changes instead of timestamps alone...

-dhruva

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Re: timestamps not git-cloned

jidanni
>>>>> "d" == dhruva  <[hidden email]> writes:

d> Also, if you clone from systems across time zones, what time do you
d> expect to set on the files.

I'm just used to tar, cpio, scp -a, rsync -a, ar, etc. using 'date +%s'
seconds internally, so no timezone problem.

I hate it when I get some latest WhizBang.tgz, only to untar it to
find all the files' dates the same, when in fact the README hasn't
been touched in seven years, but you can't tell that from ls -l. I
recall some content tracker was involved.

Of course I'll allowing you to know my delicate first day impressions.
I'm sure as I grow older I will learn the difference between content
tracker and archiver.
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Re: timestamps not git-cloned

David Brown-2-3
In reply to this post by devnull
On Fri, Nov 28, 2008 at 08:38:06AM +0530, dhruva wrote:

>I do not think there is an VCS that records timestamps.

Perforce does, at least optionally.  But, it's model is so different,
I'm not sure it really applies here.  I believe it can either be an
individual file setting, or for a whole workspace.

David
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Re: timestamps not git-cloned

Daniel Barkalow
In reply to this post by jidanni
On Fri, 28 Nov 2008, [hidden email] wrote:

> >>>>> "d" == dhruva  <[hidden email]> writes:
>
> d> Also, if you clone from systems across time zones, what time do you
> d> expect to set on the files.
>
> I'm just used to tar, cpio, scp -a, rsync -a, ar, etc. using 'date +%s'
> seconds internally, so no timezone problem.
>
> I hate it when I get some latest WhizBang.tgz, only to untar it to
> find all the files' dates the same, when in fact the README hasn't
> been touched in seven years, but you can't tell that from ls -l. I
> recall some content tracker was involved.

Well, README was just touched; it wasn't on your disk at all shortly
before. This would make a big difference if, for example, you unpacked
"foo-1.0" on top of "foo-1.1" and the timestamps were from when the files
were originally created, and now all of the source files that changed are
older than the object files and the build system does nothing.

Of course, with archives, you don't unpack different versions into the
same directory, but with a version control system, you'll do it all the
time, so you really need the system to put on disk the times when those
files were last put there. If you want to know when the README you've got
is from (and a whole lot more) "git log README" will tell you, although it
won't tell you if somebody yesterday changed the README they're
distributing from some other text to a file that's been sitting on their
disk untouched for seven years.

        -Daniel
*This .sig left intentionally blank*
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Re: timestamps not git-cloned

Johannes Schindelin
In reply to this post by jidanni
Hi,

On Fri, 28 Nov 2008, [hidden email] wrote:

> Gentlemen, it's my first git-clone,
> $ git-clone git://git.debian.org/git/pkg-fso/files.git
> and I'm disappointed to find the timestamps of the files created are
> all now and not the date of last edit.

You are mistaken to be disappointed.  Granted, to a hammer, everything
looks like a nail.  But it might make more sense to be gentle, and insert
the syringe by hand.  Maybe it will get less painful that way, too.

In other words, do not be surprised when a source code management tool
turns out to be lousy at recreating meta-data -- which has as much to do
with source code than a syringe with a nail.

Hth,
Dscho

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Re: timestamps not git-cloned

Robin Rosenberg
In reply to this post by jidanni
fredag 28 november 2008 03:24:04 skrev [hidden email]:
> Gentlemen, it's my first git-clone,
> $ git-clone git://git.debian.org/git/pkg-fso/files.git
> and I'm disappointed to find the timestamps of the files created are
> all now and not the date of last edit. At least mention something
> about this on the git-clone man page.

I recommend every new Git user to scan the FAQ. It's not just clone,
it's in everything git does in the file system. There is a very good
reason git behaves this way in general, although clone could be
exception, but then we would have a ton of questions about that
inconsistency.

-- robin
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Re: timestamps not git-cloned

Johannes Schindelin
Hi,

On Fri, 28 Nov 2008, Robin Rosenberg wrote:

> I recommend every new Git user to scan the FAQ. It's not just clone,
> it's in everything git does in the file system. There is a very good
> reason git behaves this way in general, although clone could be
> exception, but then we would have a ton of questions about that
> inconsistency.

No, clone cannot be an exception.  The information is just not stored, and
for a good reason: a file's timestamp is nothing you want to commit in
source code management.  It just does not make sense at all.

Ciao,
Dscho

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Re: timestamps not git-cloned

Peter Krefting
In reply to this post by devnull
Hi!

dhruva:

> I do not think there is an VCS that records timestamps. Only file
> contents are tracked.

CVS sort of does. The initial checkout sets the time stamp of files to
their last *check-in* time (and you can import a file with -D to set
its commit time to the current timestamp). Updates do, however, set to
current time (to not break make and friends).

I miss this behaviour in Git, but I have learnt to live with it. I
guess it is like a difference in philosophy on what time-stamps are
supposed to record, like how UNIX "cp" sets the time of the new-born
copy to now, while DOS "copy" sets it to the old time-stamp. Coming
to Unix and Linux from DOS (via OS/2), I find "cp" behaviour weird. But
have learnt to live with it (and use "cp -a" a lot).

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Re: timestamps not git-cloned

Chris Frey
In reply to this post by jidanni
On Fri, Nov 28, 2008 at 01:06:00PM +0800, [hidden email] wrote:
> I hate it when I get some latest WhizBang.tgz, only to untar it to
> find all the files' dates the same, when in fact the README hasn't
> been touched in seven years, but you can't tell that from ls -l. I
> recall some content tracker was involved.

If this is the important bit, perhaps git-archive could be changed
to create tarballs with file timestamps based on their commit dates.

- Chris

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Re: timestamps not git-cloned

Stephen R. van den Berg
Chris Frey wrote:
>On Fri, Nov 28, 2008 at 01:06:00PM +0800, [hidden email] wrote:
>> I hate it when I get some latest WhizBang.tgz, only to untar it to
>> find all the files' dates the same, when in fact the README hasn't
>> been touched in seven years, but you can't tell that from ls -l. I
>> recall some content tracker was involved.

>If this is the important bit, perhaps git-archive could be changed
>to create tarballs with file timestamps based on their commit dates.

Based on the principle of least surprise, I'd consider this a rather good
idea.
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To people that say "I could care less" - well, why don't you?
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Re: timestamps not git-cloned

Thomas Rast
Stephen R. van den Berg wrote:
> Chris Frey wrote:
> >If this is the important bit, perhaps git-archive could be changed
> >to create tarballs with file timestamps based on their commit dates.
>
> Based on the principle of least surprise, I'd consider this a rather good
> idea.

Unless I'm missing something, this would make git-archive rather more
expensive than it is now: Tree objects do not record any timestamps,
so figuring out the last commit that changed a file requires a full
history walk in the worst case[*].  (This is another side-effect of
not versioning files.)  On the other hand, current git-archive's
running time depends only on the size of the tree-ish given, including
all subtrees and blobs.

My unscientific guesstimates on how much work this would be, in a
random (old) linux-2.6 clone:

  $ git rev-parse HEAD
  e013e13bf605b9e6b702adffbe2853cfc60e7806
  $ time git ls-tree -r -t $(git rev-list HEAD~5000..HEAD) >/dev/null

  real    0m1.385s
  user    0m1.164s
  sys     0m0.220s
  $ git rev-list HEAD | wc -l
  117812

So reading (and dumping) all those trees and subtrees incurs a penalty
on the order of 30 seconds.  Compare to the current running time of
git-archive:

  $ time git archive --format=tar HEAD >/dev/null

  real    0m2.790s
  user    0m2.684s
  sys     0m0.072s

Of course, the ratio will keep getting worse as history gets longer.

- Thomas

[*] I think to really have a "worst case" here, you need at least one
file in every leaf directory that has not changed since the root
commit, and another that changes in every commit to force the search
to really read every subtree.

--
Thomas Rast
trast@{inf,student}.ethz.ch




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Re: timestamps not git-cloned

jidanni
Well all I know is from the simple user who does e.g.,
# aptitude install linux-doc-2.6.26
# ls -lt /usr/share/doc/linux-doc-2.6.26/Documentation/
he thinks "gosh, can't tell what's new vs. what hasn't changed in years".

OK, now I know why this is tolerable upstream: they all use git.

But for the lowly user downstream who gets what git-archive produces,
it seems like a step backwards: "who threw away the timestamp of when
each file was last changed?".

OK, http://git.or.cz/gitwiki/ContentLimitations says this is by design.

And OK, thinking "file by file" is old fashioned, I read. The non-git
end user should just get used to reading ChangeLogs, if any, and stop
doing ls -lt.

But you must admit, /usr/share/doc/linux-doc-2.6.26/Documentation/
etc. are aimed for reading without git.

Anyways, if just in case any individual file modification time
information can still be pried from the 40 byte IDs or whatever, I
would suggest using it by default in git-archive at least, and maybe
even git-clone etc.

Just letting you know my 'valuable first impressions'. I expect once I
start smoking more of this "git" stuff, I too will become comfortably
numb to aforementioned lowly user problem, so you would never know
unless I hereby first told you before it was too late.
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Re: timestamps not git-cloned

Sitaram Chamarty
In reply to this post by Thomas Rast
On Sat, Nov 29, 2008 at 3:46 PM, Thomas Rast <[hidden email]> wrote:

> Stephen R. van den Berg wrote:
>> Chris Frey wrote:
>> >If this is the important bit, perhaps git-archive could be changed
>> >to create tarballs with file timestamps based on their commit dates.
>>
>> Based on the principle of least surprise, I'd consider this a rather good
>> idea.
>
> Unless I'm missing something, this would make git-archive rather more
> expensive than it is now: Tree objects do not record any timestamps,

How many people use git-archive and how many times a day do they use
it?  For example, kernel.org seems to put out linux-2.x.y.z.tar.bz2
once every 2 to 7 days.

The overhead of this new option (and certainly it should be an option,
not the default) should be measured not against the old running time,
but against the frequency of usage of the tool.  Look at it on those
time scales, it may not be a big deal.

By all accounts, this overhead will not affect the "giterate" [meaning
git-literate ;-)] people too much.
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Re: timestamps not git-cloned

Andreas Ericsson
In reply to this post by jidanni
[hidden email] wrote:
> Well all I know is from the simple user who does e.g.,
> # aptitude install linux-doc-2.6.26
> # ls -lt /usr/share/doc/linux-doc-2.6.26/Documentation/
> he thinks "gosh, can't tell what's new vs. what hasn't changed in years".
>

They won't be able to do that anyway, since a spelling correction
would update the timestamp anyway. The only way of finding out if
there are *content* changes (which is really what matters) is to
use some sort of history-browser for those documents. Git is good
for that. The sort of people who really need to know when the docs
change can be exptected to have a higher technical knowledge than
the end-users, so it's not too much to ask that they use such a
history browsing tool to find out what's new (or simply "diff").

Either way, timestamps on documents are a very poor way of finding
out when something really changed.

> OK, now I know why this is tolerable upstream: they all use git.
>
> But for the lowly user downstream who gets what git-archive produces,
> it seems like a step backwards: "who threw away the timestamp of when
> each file was last changed?".
>
> OK, http://git.or.cz/gitwiki/ContentLimitations says this is by design.
>
> And OK, thinking "file by file" is old fashioned, I read. The non-git
> end user should just get used to reading ChangeLogs, if any, and stop
> doing ls -lt.
>
> But you must admit, /usr/share/doc/linux-doc-2.6.26/Documentation/
> etc. are aimed for reading without git.
>

Well, /usr/bin/less doesn't require git to function, so I fail to see
what the fuzz is all about.

> Anyways, if just in case any individual file modification time
> information can still be pried from the 40 byte IDs or whatever, I
> would suggest using it by default in git-archive at least, and maybe
> even git-clone etc.
>

It can, but it's a fairly expensive operation, tracking each files
SHA1 backwards in time to see when the commit was done that last made
any changes to it. It's not something you want to do for an archive
containing 26K files. Trust me on this.

> Just letting you know my 'valuable first impressions'. I expect once I
> start smoking more of this "git" stuff, I too will become comfortably
> numb to aforementioned lowly user problem, so you would never know
> unless I hereby first told you before it was too late.


I see a lot of ranting but no patches from you. Since you're the one
with the itch, why not just submit a patch and see if distro packagers
start using it?

Some words of advice though; Make it optional, or it'll be dropped on
the floor. For bonus points, make it calculate timestamps only for a
path-spec delimited set of files. That'll cut down expected runtime
by a *huge* amount for something like the linux kernel.

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Re: timestamps not git-cloned

Jakub Narębski
Andreas Ericsson <[hidden email]> writes:

> I see a lot of ranting but no patches from you. Since you're the one
> with the itch, why not just submit a patch and see if distro packagers
> start using it?
>
> Some words of advice though; Make it optional, or it'll be dropped on
> the floor. For bonus points, make it calculate timestamps only for a
> path-spec delimited set of files. That'll cut down expected runtime
> by a *huge* amount for something like the linux kernel.

I think the old idea of 'tree blame' (search archives) would be a good
interface for this feature... if you decide to write it.

--
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Poland
ShadeHawk on #git
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