Branching a kernel-sized tree uses a lot of RAM

[Gerald (Jerry) Carter]

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John,

> https://launchpad.net/products/bzr/+bug/45310
> 
> I filed that bug on this problem a while back, 
> and right now the problem still exists. A lot of
> my other concerns about bzr's performance have
> already been addressed (thanks everyone!) but 
> this one still persists, and is one of my
> last bzr complaints :).
> 
> Branching a freshly imported vanilla kernel branch uses 
> no less than 1GB RAM, during the "Building" phase
> (both with working trees and without). This makes it
> pretty hard to work with kernel-sized trees even on fairly
> modern hardware. In contrast, importing the same 2.6.17 
> vanilla kernel requires only 55MB or so of RAM,
> so there is something specific to branching (the
> Build phase particularly... the fetch phase is good about
> RAM usage) that eats RAM.

Funny.  I just got some complaints from one of our
summer developers regarding merge.  I'm mirroring
an svn tree using a simple shell script
(http://people.samba.org/bzr/jerry/slag/scripts/bzr-svnmirror).
The SAMBA_4_0 svn tree has about 9000 commits
so the bzr mirror weighs in about 132M.  104M of that is
in .bzr/.  SO in my case, the memory usage seems to
related to a large history and not the source of the
source.  But I'm still running some tests to reproduce
original complaint.

So I tarred a snapshot people could download, extract
and then run "bzr pull" to update.  Then they could
"bzr branch" against that.

S P wrote:
>
> Nothing fundamentally wrong with bzr, my specific
> configuration is probably what's causing the problem.
> The most recent problem seems to be a huge amount
> of memory that bzr (using 236M I think) uses during
> the bzr merge operation on the 74MB archive.  I have
> 160MB RAM + 256 MB swap and both were filled leading
> to thrashing. Eventually, I killed bzr. Was
> still showing "phase 0/4" for a very long time
> (~20 minutes). I should be able to increase swap
> space and try again.
>
> Another "complication" is the initial setup cost:
> 74MB for a local mirror versus 7MB for the SVN
> checkout (of Samba 4 code). SVN was quickly running,
> but downloading bzr archive over dial-up was
> problematic. Thankfully, I now have DSL installed
> (yesterday), and this shouldn't cause problems anymore.
>
> I think once the merge operations are over and local
> mirrors established, it should be smooth sailing.
> I'll try again later.






cheers, jerry
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