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Bug#571457: svnserve hangs, burning CPU cycles, under low TCP sendbuffer.

From: Dr. Andreas Krüger <andreas.krueger_at_dv-ratio.com>
Date: Thu, 25 Feb 2010 16:16:25 +0100

Package: subversion
Version: 1.6.9dfsg-1
X-Debbugs-CC: dev_at_subversion.apache.org

Hello, Subversionists,

I have a subversion repository with a single revision, consisting of a
single roughly 10 MB file with random data.

I use svnserve to serve that repository.

I use a client to access the svnserve over the network, via "svn co".

(The client happens to be Ubuntu's 1.6.5dfsg-1ubuntu1, in case that
matters.)

The server is an openvz guest. When, on the corresponding host, I set

vzctl set NNN --tcpsndbuf 415k:715k

or lower (my guess is the first number is the one that matters), the
checkout starts, there is some initial network traffic, but then
svnadmin starts to eat up all CPU cycles it can get and no further
progress is made, until I kill the svnadmin process manually on the
server. Just killing the client does not seem to stop the waste of CPU
cycles on the server.

When I increase the tcpsndbuf above that value, there is no problem.

However, when I check in a much larger file into the repository (I do
that directly, using file:/// - access), and try to check out again
(using svnserve), the problem reappears.

This is quite reproducibly, with svnadmin as a standalone daemon as well
as svnadmin running under inetd. For the latter case, I made no precise
experiments about the --tcpsndbuf numbers.

This is the summary. I have written three mails yesterday and today to
the dev_at_subversion.apache.org mailing list, but have not received any
answers there yet. There is lots of nitty-gritty background information
in those mails, which, hopefully, you'll be able to find here:

http://mail-archives.apache.org/mod_mbox/subversion-dev/201002.mbox/browser

Regards, and thank you for providing fine software,

Andreas

P.S.: I ask the Debian bug tracking system to forward a copy of this
mail to the SVN dev mailing list. This contains two pieces of
information not available in my previous mails to that list:

* The bug is reproducible with the latest subversion software version I
can easily install, short of compiling myself.
* The client I'm using is, and always has been, 1.6.5dfsg-1ubuntu1. I
think I misquoted it to be 1.5 in one of my earlier mails. I apologize
if this caused any confusion!

-- 
Dr. Andreas Krüger, Berater, DV-RATIO NORDWEST GmbH
andreas.krueger_at_dv-ratio.com
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Received on 2010-02-25 18:35:35 CET

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