Some timings using bzr

[James Westby]

On Fri, 2008-07-11 at 08:21 +0200, David Ingamells wrote:
> A simple copy of the repository (including the .bzr directory) from
> NFS to a local disk on desk01 takes 3.1 seconds and NFS to NFS takes
> 84 seconds at a low-load time of day. Clearly there is significant
> room for improvement in bzr when you compare the closest bzr
> equivalents to this copy  (36 and 187 seconds). From an admittedly
> very naive perspective, the branch bzr makes is only a copy of the
> repos (when branch is used without options).

The branch command does do more than this. Firstly it only pulls
the revisions out of the repository that are present in the history
of the branch, so it must walk the revision graph, and can't just
do a plain copy. Secondly it does some integrity checking so that,
for example, disk corruption would not propogate to the new branch.
This obviously leads to some overhead. I'm not sure whether that
justifies all of the difference that you saw, someone who has profiled
the operation would be able to tell you if there was any wasted
effort there, and so the operation could be sped up.

Thanks,

James