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Re: Hung httpds process consuming 100% CPU

From: Tony Butt <tjb_at_cea.com.au>
Date: 2007-04-23 01:34:39 CEST

Mark W. Shead wrote:
> Has anyone run into problems with httpds.prefork hanging and consuming
> 100% of a CPU? This is on a 4 processor box. Every few days a
> process will start consuming 100% of one of the available CPUs and
> just sit their indefinately. Once a few of the CPUs are running these
> hung processes, subversion becomes very slow and unusable.
>
> Any suggestions?
>
> OS: RHEL 3
> SVN: 1.3.2
> Apache: 2.0.54
> Server: 4 processors
>
> Mark Shead
>
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We recently had that problem - our problem seemed to be mod_auth_ldap.

Our history is as follows:

We originally set up on SuSE Enterprise Linux 9 running apache 2.0.49,
and built mod_auth_krb to authenticate against a Windows 2000 Domain Server.
All was good with this setup, except that mod_auth_krb really hammered
the DNS when used with subversion, as it doesn't cache credentials, and
the Kerberos configuration file used hostnames.
I changed the Kerberos configuration to use IP addresses, and we ran
happily like that for about 2 years.

Then, our IT people 'upgraded' the Windows 2000 servers to Windows 2003,
and mod_auth_krb failed (2003 is fussier about some details). When we
got the credential setup correct, it worked fine for basic web access,
but an order of magnitude slower for subversion access, which was
unacceptable to us.

As an alternative, I managed to configure mod_auth_ldap and mod_ldap to
authenticate against the 2003 servers for subversion, and all was well
for a week or so.
When we built up some confidence, we integrated the mod_auth_ldap
configuration into the rest of the web server (trac, websvn, TWiki, etc).
Soon after this, we started to notice the http process spinning, and
consuming all available CPU. After undoing every change we could find
(to no effect), and some frantic web research, I found some references
to this relating to the mod_ldap caching of credentials. I disabled the
caching by setting
  LDAPCacheEntries = 0
in the apache configuration. We have not seen the problem since.

Tony Butt
CEA Technologies
Canberra, Australia

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Received on Mon Apr 23 01:36:20 2007

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