thinking about my really bad performance

Wichmann, Mats D mats.d.wichmann at intel.com
Sat Nov 24 01:06:03 GMT 2007


I've moaned a few times about performance issues.
Recently very simple (to the user! :-) operations
have occasionally become very slow.

On a branch I've reported on before - it's old
(converted from cvs using tailor), moderate size
(5500 files in working tree, 16000 in .bzr), and
about 1500 total revisions....  I just had an
occasion where I checked in a two-character change
to one file (specifically, removed quotes around
something). Completely local branch.  This took 205 
seconds, most of the time spent looking at message like 

Collecting changes [Directory XXX]   

some delay, speed through several directories,
some delay, etc.

Needless to say, that's a bit longer than one would
like to give to such an operation.

I'm pretty convinced that the issue here is the huge
number of files that need to be processed to find out
what the commit consists of, and a relatively small
system (it's actually a Linux virtual machine allocated
640 meg of memory) such that the buffer cache has
a really good chance of not containing any of the
information about the .bzr metadata. The operation
of just editing the file won't have brought in any.

If I uncommit the change and commit it again without
doing anything else, a situation that ought to have
the best possible data set in the buffer cache, the
time drops to something like 8 seconds, which is a
pretty substantial difference.


For now, just reporting...

-- mats



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