Re: reducing object store size with remote alternates or shallow clone?

From: Brandon Casey <brandon.casey.ctr@nrlssc.navy.mil>
Date: Aug 24, 2010, 23:29 UTC
Message-ID: <pzml8liT3RErVlMrdxbSkHmhBs1RMvwYma9UXgvG6WY@cipher.nrlssc.navy.mil>
In-Reply-To: <7vfwy3vnti.fsf@alter.siamese.dyndns.org>

On 08/24/2010 01:59 PM, Junio C Hamano wrote:

Show 20 quoted lines

> Brandon Casey <brandon.casey.ctr@nrlssc.navy.mil> writes:
> 
>> On 08/24/2010 11:45 AM, Junio C Hamano wrote:
>>
>>> How about doing
>>>
>>>     $ LINUS=git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
>>
>>>     $ git fetch $LINUS
>>>     $ git bundle create myfork.bundle HEAD..master
>>
>> I think you mean
>>
>>       $ git fetch $LINUS master
>>       $ git bundle create myfork.bundle FETCH_HEAD..master
> 
> Thanks, of course you are right.
> 
> Strictly speaking, as I know there is only one branch in the repository of
> Linus, there is no need to say "master" when fetching

Hmm. It appears that if the current checked-out branch has a configured merge ref, then a fetch that supplies a repository url (not a remote name) and no fetch refspec, will not fall back to fetch HEAD from the remote repository.

i.e. the following fetch does not retrieve any objects nor update FETCH_HEAD

   $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git linux
   $ cd linux
   $ git fetch git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git

but, if you create a new branch, that has no merge ref configuration, then git behaves as expected:

   $ git branch foo
   $ git checkout foo
   $ git fetch git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git

Namely we retrieve new objects and update FETCH_HEAD:

   From git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6
   * branch            HEAD       -> FETCH_HEAD

I think the problem is in builtin/fetch.c: get_ref_map().

When fetch is called as above, with a repository url but no refspec, we get this call sequence:

   cmd_fetch -> fetch_one
     fetch_one -> do_fetch(argc = 0)
       do_fetch -> get_ref_map(ref_count = 0)
         line 148: has_merge is assigned 1 since the current checked out
                   branch has a merge ref configured
         The 'if' branch is entered, the 'for' loop is not entered,
         ref_map retains its NULL initialization value and
         get_ref_map() returns NULL
       do_fetch -> fetch_refs(ref_map = NULL)
         and the transports do nothing since no refs have been requested

Perhaps the fix should look something like this (warning copy/paste):

diff --git a/builtin/fetch.c b/builtin/fetch.c
index fab3fce..218e71d 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -146,7 +146,8 @@ static struct ref *get_ref_map(struct transport *transport,
                struct remote *remote = transport->remote;
                struct branch *branch = branch_get(NULL);
                int has_merge = branch_has_merge_config(branch);
-               if (remote && (remote->fetch_refspec_nr || has_merge)) {
+               if (remote && (remote->fetch_refspec_nr || (has_merge &&
+                               !strcmp(branch->remote_name, remote->name)))) {
                        for (i = 0; i < remote->fetch_refspec_nr; i++) {
                                get_fetch_map(remote_refs, &remote->fetch[i], &tail, 0);
                                if (remote->fetch[i].dst &&


-Brandon