From: Brad Malone
To: git-users@googlegroups.com
Sent: Thursday, May 10, 2012 5:07 PM
Subject: Re: [git-users] Re: Basic question: confusing messages with git merge
Thomas and Antony,
Thank you both for taking time to write such detailed responses to my
question! Now let me get to what you both have said individually.
Thomas,
Thanks for the notes on rebasing. From what I understood from reading git
tutorials before was that rebasing was something which was usually nice to do
whenever one has local changes (for which no commits have ever been made to the
remote branch) so that the git history looks more linear. I have planned on
using rebasing later on when my git usage becomes more complex, but currently I
only work on my own private repo for which I *attempt* to always update before
making local changes. So 99% of my work simply involves updating whatever local
computer (I work on different computers) to the work that exists on my remote,
doing my stuff, and then committing back. I believe that this current problem
of mine is probably more due to the fact of an accidental 'git merge origin
master' command.
Antony,
I'm glad you think that this may have been the problem (since I really would
like to understand why it happened). I had seen the octopus merge when looking
in the documentation and online and figured that what might have been what
happened. What I did *not* know was that this was old and no one really uses it
anymore. Glad to know this so I don't try to incorporate it into my workflow
(presumably there would be no need anyway or other people would use it as
well).
Yes, I see empty merge commits when this sort of thing happens. I am familiar
(although probably no expert) with tracking of remote branches. My local master
branches are always set up to track origin/master (see 'git remote' command
below)
bmalone@papabear:~/repos/my_codes$ git remote show origin
Password for 'https://gammapo...@bitbucket.org':
* remote origin
Fetch URL: https://gammapo...@bitbucket.org/GammaPoint/my_codes.git
Push URL: https://gammapo...@bitbucket.org/GammaPoint/my_codes.git
HEAD branch: master
Remote branch:
master tracked
Local branch configured for 'git pull':
master merges with remote master
Local ref configured for 'git push':
master pushes to master (local out of date)
, and so technically I should be able to use 'git pull' and merge
automatically. This is actually what I did when I started using git a couple
weeks ago. However, the reason I stopped doing was twofold:
1). I found that when I used 'git pull' that if I used 'git status' I would
always find out that my local branch was some number of commits ahead of
origin/master (this was in fact unrelated to me having made any local commits).
I think the cause of this was actually that 'git pull' doesn't update my local
copy of where origin/master is (which is what 'git fetch' does I think). I
suppose I could use 'git fetch' followed by 'git pull', but I wasn't sure if
that was the correct thing to do, mostly because of reason #2. Edit: Also I
think it is true that people say that 'git pull' IS equivalent to a fetch and
then a merge, but this never seemed to be the case for me because origin/master
position was never updated. If I have to type in something like 'git remote
update origin' then it seems that 'git pull' isn't saving me any typing. I hope
I am making sense here. This problem is discussed constantly online (see
http://stackoverflow.com/questions/4843881/updating-branches-using-git-pull and
http://stackoverflow.com/questions/277077/why-is-git-telling-me-your-branch-is-ahead-of-origin-master-by-11-commits-a)
but I haven't seen anyone answer it to much satisfaction.
2). This article: http://longair.net/blog/2009/04/16/git-fetch-and-merge/
suggests that one should fetch and then merge rather than pull. This made me
think that the pair fetch/merge was the best replacement for pull, and since
pull wasn't updating the position of origin/master, I stopped using it.
Is this understanding I have correct?
Thanks again,
Brad
Brad,
One useful resource is
http://ndpsoftware.com/git-cheatsheet.html#loc=remote_repo; (linked from
http://git-scm.com/docs). It shows most of the different places that your data
may be located at, and the commands between them.
One of the areas that can confuse is the distinction between the true remote
repository, and your local copy based on last time that particicular computer
looked at it (e.g. upstream/master) .
Clicking on "Upstream" column will show the commands that will transfer data
between the upstream remote, and you are using Bitbucket as your common
reference point. So you do need to remember to look at it i.e. 'fetch'
immediately you start on the other computer, and at the end of the session,
'push' your latest and greatest back to Bitbucket.
The status that reports the both "ahead xx comits" and "clean: nothing to
commit" is because they are different comparisons. The first is between the
upstream [1], and your last local commit, while the second is between your last
local commit and your actual files. If you are sharing a project, your mate may
have pushed an extra commit that you weren't aware of (or that you'd forgotten).
[1] - I think the difference is between your local copy of the remote, and your
last local commit, rather than going to the actual remote and your last local
commit. Without a fetch[2], you can't do the merge of the commits sourced from
the distant repo, hence my expectation.
[2] - There has been a lot of dicussion on the main git list about an upcoming
change about which brances are pushed by default which can suprise some,
especially as which branches are being fetched isn't the same.
Philip
On Thu, May 10, 2012 at 4:39 AM, Antony <antony.m...@gmail.com> wrote:
Hi,
On Thursday, 10 May 2012 00:49:15 UTC+1, Brad wrote:
What do these things mean? I'd imagine that 'Merge remote-tracking branch
origin/master' should have been what happens when I type 'git merge
origin/master', but what about the other? Could 'Merge branch master,
remote-tracking branch origin' be what happens if I accidentally typed "git
merge origin master"? If I do this, what happens exactly?
Good guesswork!
One of git's merge algorithms is called an 'octopus merge', and merges more
than two branches together. When you run 'git merge origin master', the fact
that you named two branches (OK, 'origin' isn't a branch, but bear with me)
causes the octopus merge algorithm to be invoked.
However, this algorithm is pretty old, no-one really uses it any more, and
it's normally regarded as nothing more than a curiosity. Therefore it doesn't
receive much love, and has some rather odd corner cases and bugs.
One such corner case is when one of the branches it's given to merge isn't
a branch at all, and is instead the name of a remote. When this happens, you
get the message you described, and some other stuff -- an empty merge commit I
think? And I seem to recall there's another very strange oddness.
So, long story short, do not type 'git merge origin master'.
If you want an easier way to merge (with less typing) read on...
Do you know about git's branch tracking stuff? Basically, you can assign
each branch an 'upstream' branch (defined in git's config). When you run 'git
pull', git will merge in this upstream branch by default. ('git push' follows a
different set of rules by default, although this might change. Read
push.default in man git-config for now).
When a branch has an upstream configured, '@{upstream}', or '@{u}' points
to that upstream branch. You can also see whether a branch has an upstream by
typing 'git branch -vv' -- the upstream appears in square brackets.
So, to configure an upstream (if you don't have one set already), use 'git
branch --set-upstream master origin/master', or 'git push -u origin master' if
you want to push at the same time.
Having done this, you can type 'git merge @{u}' (with master checked out)
to merge origin/master into master.
Hope that cleared up some confusion.
Antony
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