On Wed, 9 Nov 2005, Colm MacCarthaigh wrote:
> On Tue, Nov 08, 2005 at 12:36:04PM +0100, Dag Wieers wrote:
> > I don't know what the problem is. Either the file is empty on the
> > filesystem (corruption on the filesystem level or problems with rsync or
> > NFS) or the web server is handing out empty files under certain
> > conditions.
>
> It's the latter, and the problem has been traced to yet another bug to
> do with sendfile() and TCP checksum offloading. Basically ... the
> packets were being sent, but with invalid checksums. So the clients were
> rejecting the packets.
>
> > Without access to the system I have no clue whether the filesystem is the
> > problem or it is Apache related. I bet it is Apache's problem as mirrors
> > of Heanet do not seem to have this problem. (This is different than when
> > it was a NFS problem with the same symptoms)
>
> Turned out not to be an Apache problem, as anything which used
> sendfile() would have been effected. The problem is really in the
> network cards - and how they handle offloaded checksums when DSCP
> headers are set.
Thanks Colm, I'm very interested to learn how you figured this out.
Also, are there any tests/monitors to find the same cause in the future ?
It could be something that is silently bothering other people as well, and
a technical explanation together with Google might make this valuable
information.
Kind regards,
-- dag wieers, dag@xxxxxxxxxx, http://dag.wieers.com/ --
[all I want is a warm bed and a kind word and unlimited power]
