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nscd and large group problem...


From: John R. Hover
Subject: nscd and large group problem...
Date: Fri, 22 Mar 2002 17:24:43 +1200
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:0.9.8) Gecko/20020212

Nscd, (or at least nscd on RedHat) fails upon an 'ls -l' on a directory with files owned by a group with a large number of users (in this case 2800), or a getent group <Groupname> of same. This occurs regardless of the suggested-size (or TTL, NTTL) in /etc/nscd.conf. The nscd processes continue to run, but stop responding (one always becomes <defunct>)-- and the 'ls -l' or 'getent group <blah>' command never completes. By the time nscd fails, it's memory usage has always climbed from the initial 1600k up to 4-5 MB. The exact point varies.

We encountered the problem using nsswitch and nss_ldap.so, and thought for a long time that it had something to do with our LDAP setup. That's why I've sent this to the nss_ldap list. Someone else may be having the same confusion.

I've confirmed that it still happens if the group is local to /etc/group-- which suggests it is a more fundamental problem with glibc/nscd! It shouldn't be hard to reproduce.

A group with approx. 1400 users does *not* cause the problem.
A group with approx. 2800 users *does* cause the problem.

SYSTEM CONFIG
Numerous computer models (HP, Compaq, Dell) i686/386 architecture
OS:   Linux Red Hat 7.2
Kernel: Several from Redhat default up to latest 2.4.9-31--didn't try a custom compiled kernel.

Versions:  glibc|nscd-2.2.4-13, 2.2.4-19.3, 2.2.4-20
( I downloaded and rebuilt the glibc-2.2.4-20 SRPM, installed all the resultant RPMS. Same problem. ) For probably obvious reasons, I didn't build glibc from source without Redhat patches, so I can't be sure this isn't Redhat specific.

nss_ldap-172-2 : doesn't cause problem because it doesn't return member list for groups with more than 23 users

nss_ldap-184 : latest version, which correctly returns all members of a group. This causes the problem when nscd is on. It works fine when nscd is off.

As I am not a programmer, I'm not really capable of getting any deeper into strace or debugging efforts. I figured someone here would want to reproduce it and see that it gets to the right person. I thought about submitting something to bugzilla.redhat or www-gnats.gnu.org, but I figured a "this fails" description without debugging info wouldn't be of much use.

Does anyone know anywhere else I should CC this?

Cheers,


--john


--
John R. Hover
Unix/Linux System Analyst
Department of Computer Science
University of Auckland




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