Hi,
On Sat, 26 Jul 2008, Linus Torvalds wrote:
> > Is there a way to change that default?
>
> Use an alias or something.
This doesn't help with the graphical front ends and they only use what git
gives them.
> To see why it's the default, do a few tests. In particular, try it with
> gitk on the kernel. Try it on some fairly simple file that doesn't get a
> lot of churn. Example:
>
> gitk lib/vsprintf.c
>
> vs
>
> gitk --full-history lib/vsprintf.c
>
> and if you don't _immediately_ see why --full-history isn't the default,
> there's likely something wrong with you. One is useful. The other is not.
>
> So we absolutely _have_ to simplify merges. There is no question about it.
Well, I don't want that much history.
Let's take a different example. Look at kernel/sched_rt.c with git-log,
--full-history shows an extra commit of a patch which was committed and
merged twice, but there is no information how this other patch was merged.
If you have giggle installed, you'll see that commit as a loose end.
(I have git version 1.5.6.2 installed in case it matters.)
> That said, we currently simplify merges the simple and stupid way, and
> I've hinted several times on this mailing list that there is a better way
> to do it (last time it was the discussion about "filter-branch".
>
> In fact, if you google for
>
> filter-branch full-history
>
> you'll find some of the discussion. In order to make --full-history useful
> as a default, we'd need to do an after-the-fact merge cleanup (ie remove
> lines of development that are later found to really be totally
> uninteresting), but that is *hard*.
I played a little with it in the ruby script below, which produces a
complete connected graph of all content nodes and which have been merged
into the head, e.g. for sched_rt.c it produces that extra commit merge.
The script basically eliminates all empty merges. As input to the script I
used "git log --parents --name-only --full-history kernel/sched_rt.c |
grep -e ^commit -e ^kernel", which seems to produce the same amount of
commits as "gitk --full-history ...".
The main function is to check, whether one parent of a commit is an
ancestor of another parent, so that this path can be eliminated. I tried
it with other paths and too simple implementations quickly lead to
exponential behaviour. :) It probably also shouldn't be recursive, I had
to increase the stack limit, otherwise I got stack exceptions.
Otherwise it seems to work fine, it wasn't that hard :-)
The ruby syntax shouldn't be too hard too read, the nonobvious thing is
maybe that '$' marks global variables.
bye, Roman
#! /usr/bin/ruby
$parent = Hash.new
$content = Hash.new
$result = Hash.new
commit = nil
head = nil
while l = $stdin.gets
a = l.split(" ")
if a[0] == "commit"
commit = a[1]
head = commit unless head
$parent[commit] = a[2..-1]
else
$content[commit] = true
end
end
$parent_check = Hash.new
$parent_cache = Hash.new
def commit_has_parent?(commit, commit2)
if $parent_check[commit]
print "parent loop for #{commit} (#{commit2})?\n"
p $parent_check
return false
end
return $parent_cache[commit] if $parent_cache.has_key?(commit)
$parent_check[commit] = true
res = false
if $content[commit] > $content[commit2]
$parent[commit].each do |parent|
if parent == commit2 || commit_has_parent?(parent, commit2)
res = true
break;
end
end
end
$parent_cache[commit] = res
$parent_check.delete(commit)
$parent_cache.clear if $parent_check.empty?
return res
end
def check_commit(commit)
return $result[commit] if $result.has_key? commit
a = Array.new
$parent[commit].each do |parent|
parent = check_commit(parent)
if parent
a.each_index do |i|
if a[i] == parent || commit_has_parent?(a[i], parent)
parent = nil
break
elsif commit_has_parent?(parent, a[i])
a[i] = parent
parent = nil
break
end
end
end
a.push(parent) if parent
end
$parent[commit] = a
$content[commit] = true if a.size > 1
if $content[commit]
$result[commit] = commit
max = 1
a.each do |parent|
max = $content[parent] + 1 if max <= $content[parent]
end
$content[commit] = max
else
$result[commit] = a[0]
end
return $result[commit]
end
check_commit(head)
#p $result
#p $parent
p $content.keys.size
$content.each_key do |commit|
p [ commit, $parent[commit] ]
commit = $parent[commit][0]
end
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