The original comment was not really correct.  This does complete after about 30 minutes, however it takes under 30 seconds with fedora 20, so there is still something amiss here.

Created attachment 957866 [details]
Testcase

This is a simplified snippet from my Firefox build procedure which exhibits the issue.

Here is the output from "time hg pull" using the mercurial-3.0-2.fc21.x86_64 package that is the current fedora 21 version:

pulling from http://hg.mozilla.org/mozilla-central/
searching for changes
adding changesets
adding manifests
adding file changes
added 742 changesets with 4957 changes to 2526 files
(run 'hg update' to get a working copy)

real    25m31.661s
user    25m26.505s
sys     0m1.244s

After downgrading to the mercurial-2.8-1.fc20.x86_64 package, as you can see it goes from over 25 minutes to under 9 seconds:

pulling from http://hg.mozilla.org/mozilla-central/
searching for changes
adding changesets
adding manifests
adding file changes
added 742 changesets with 4957 changes to 2526 files
(run 'hg update' to get a working copy)

real    0m8.746s
user    0m6.540s
sys     0m0.702s

All of the extra time taken occurs between the time it outputs the line "added 742 changesets with 4957 changes to 2526 files" and the line "(run 'hg update' to get a working copy)".

I've reported this upstream, see what they have to say...

Can you try the 3.2 build in:

http://copr-be.cloud.fedoraproject.org/results/nbecker/mercurial-3/

(In reply to Neal Becker from comment #5)
> Can you try the 3.2 build in:
> 
> http://copr-be.cloud.fedoraproject.org/results/nbecker/mercurial-3/

I can try that but further testing seems to make it seem that the real issue here is that there is some kind of first time version 2 to version 3 conversion that is not happening if you take a version 2 bundle and do and hg init hg unbundle 
and it gets done at the next pull

I tried going back a few revs and doing an hg clone of this repository and it is doing the same long seeming to not be doing anything at the same point.  I bet the pull will go lickety split.  after that I will try this 3.2 version.  if the issue had originally occurred at the unblundle step I would have recognized it as a version difference thing.  but the unbundle and pull are happening with the same version so you would not expect that to b
e where any such conversion occurs.

Please see:

http://comments.gmane.org/gmane.comp.version-control.mercurial.devel/74545

It is claimed that this bug is almost certainly fixed in 3.1+.

I'm just the messenger here, I'm not an expert on hg.

(In reply to Neal Becker from comment #7)
> Please see:
> 
> http://comments.gmane.org/gmane.comp.version-control.mercurial.devel/74545
> 
> It is claimed that this bug is almost certainly fixed in 3.1+.
> 
> I'm just the messenger here, I'm not an expert on hg.

Yes thsi seems to fix it.  Thank you so much!

Good.  I'll try to see what I can do to update (it has to be coordinated with tortoisehg)

tortoisehg-3.2.1-1.fc21,mercurial-3.2.2-1.fc21 has been submitted as an update for Fedora 21.
https://admin.fedoraproject.org/updates/tortoisehg-3.2.1-1.fc21,mercurial-3.2.2-1.fc21

Hmm this is closed, however, the update (which should probably really be to 3.2.3) is still not available via fedora updates.