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Re: Surely 'bzr update' shouldn't be this slow?

From: Stefan Monnier
Subject: Re: Surely 'bzr update' shouldn't be this slow?
Date: Thu, 07 Jan 2010 10:06:25 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1.50 (gnu/linux)

> I beg your pardon?  My machine is a 1.2 GHz Athlon.  That is NOT a slow
> machine by any measure, except that even faster machines are now common.

Agreed.  I use a similar machine every once in a while (Thinkpad X30)
and it's perfectly useable.  I haven't used it extensively for Emacs
hacking of late, but I have done some "bzr updates" of Emacs there and
didn't find it unbearable.
Note that Bzr is pretty memory hungry as well, so that might make
a larger difference (I have 768MB in my smallest/oldest/slowest

> Why does Bazaar need to "process" this data?  It's essentially doing
> copying, with some accompanying administrivia.  Is it doing heavy number
> crunching in Python, when it really needs a C module, or something like
> that?

The technical reason is that the repository (whether shared or not)
contains all the info for the branch you're copying, plus some more
(for other branches that are, or have been stored there, or other branches
which you have referred to from there (e.g. in a diff, merge, ...)).
So Bzr basically does a GC along the way, only extracting the bits that
are necessary, which means it unpacks and then repacks pretty much the
whole thing.

> I just did a 'bzr update' on my .../trunk.  It took 23 minutes,
> transferring nearly 200Mb to/from savannah in the process.  This compares
> with all our source files (.c, .h, .el) being ~64Mb.  Could it be that
> 'bzr update' just downloads the whole repository again?

Yes.  As mentioned, if the remote repository could be accessed via
bzr+ssh rather than sftp, it would be a bit better.

> Or has somebody else raised this issue on another thread that
> I've missed?

Of course.


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