Difference between 'git rebase' and 'git rebase -m'

Difference between 'git rebase' and 'git rebase -m'

[Joshua Jensen]

We ran into an interesting issue yesterday during a rebase.

User Bob had added a line at the same place in a (C++) .h file as User 
Joe, who had already pushed his one line change.  The natural 
expectation would be a conflict during User Bob's rebase operation, but, 
in fact, the conflicting patch applied without difficulty.

After an investigation, we discovered this particular file had a near 
duplicate of its C++ class definition immediately following the original 
but renamed into a thread-safe version; the rename of the class was the 
only change to its contents.  The default  'git rebase' operation looked 
some 150 lines into the file, discovered the patch didn't match due to 
User Joe's added line, continued scanning the file until it found 
another matching location some 300 lines later (the near duplicate 
thread-safe version of the class), and applied the patch there.

While coming up with a repro to post here, we cherry picked the 
individual changes and found the cherry pick properly conflicted.

We further discovered 'git rebase -m' (or 'git rebase -s recursive') 
also conflicted at the User Bob/Joe modification.

I can post a repro here, if needed.

I'm curious as to why 'git rebase -m' isn't the default and what the 
real difference is between 'git rebase' and 'git rebase -m'.  
Additionally, is there any documentation describing how the patch 
algorithm determines context?

Thanks!

Josh

Re: Difference between 'git rebase' and 'git rebase -m'

[Jonathan Nieder]

Joshua Jensen wrote:

> I'm curious as to why 'git rebase -m' isn't the default and what the
> real difference is between 'git rebase' and 'git rebase -m'.

git rebase is faster. :)

git rebase works by formatting a patch series and applying it.
git rebase -m uses repeated 3-way merge and should be more robust.

Re: Difference between 'git rebase' and 'git rebase -m'

[Nguyen Thai Ngoc Duy]

On Wed, Nov 17, 2010 at 1:27 AM, Jonathan Nieder <jrnieder@gmail.com> wrote:
> Joshua Jensen wrote:
>
>> I'm curious as to why 'git rebase -m' isn't the default and what the
>> real difference is between 'git rebase' and 'git rebase -m'.
>
> git rebase is faster. :)

Perhaps a config option to let people to default to -m. Or perhaps
they can just make an alias.

By the way, can we make rebase even faster? Rebasing ~20 patches or
more seems slow to me. I don't know much how patching works though.
-- 
Duy

Re: Difference between 'git rebase' and 'git rebase -m'

[Michael J Gruber]

Nguyen Thai Ngoc Duy venit, vidit, dixit 17.11.2010 12:43:
> On Wed, Nov 17, 2010 at 1:27 AM, Jonathan Nieder <jrnieder@gmail.com> wrote:
>> Joshua Jensen wrote:
>>
>>> I'm curious as to why 'git rebase -m' isn't the default and what the
>>> real difference is between 'git rebase' and 'git rebase -m'.
>>
>> git rebase is faster. :)
> 
> Perhaps a config option to let people to default to -m. Or perhaps
> they can just make an alias.
> 
> By the way, can we make rebase even faster? Rebasing ~20 patches or
> more seems slow to me. I don't know much how patching works though.

git sequencer...

Michael

Re: Difference between 'git rebase' and 'git rebase -m'

[Nguyen Thai Ngoc Duy]

On Wed, Nov 17, 2010 at 8:36 PM, Michael J Gruber
<git@drmicha.warpmail.net> wrote:
> Nguyen Thai Ngoc Duy venit, vidit, dixit 17.11.2010 12:43:
>> On Wed, Nov 17, 2010 at 1:27 AM, Jonathan Nieder <jrnieder@gmail.com> wrote:
>>> Joshua Jensen wrote:
>>>
>>>> I'm curious as to why 'git rebase -m' isn't the default and what the
>>>> real difference is between 'git rebase' and 'git rebase -m'.
>>>
>>> git rebase is faster. :)
>>
>> Perhaps a config option to let people to default to -m. Or perhaps
>> they can just make an alias.
>>
>> By the way, can we make rebase even faster? Rebasing ~20 patches or
>> more seems slow to me. I don't know much how patching works though.
>
> git sequencer...

Sequencer is definitely an improvement. But does it improve
performance? I don't know rebase internals but I think that it needs
to update worktree/index for every commit, which might slow things
down a bit.
-- 
Duy