slapd 2.3.19 freezes up

[Krishna Sivaramapuram <krishna@everyone.net>]

I have a pretty serious issue in my environment... I've around 6 million 
nodes in my ldap tree... And this server is running on a box with the 
following linux configuration...

Cent0S 4.0 (basically redhat enterprise 4.0)
upgraded to a 2.6.13.2 smp kernel

We are using Openldap 2.3.19 with BDB 4.3.29.

slapd keeps running for more than 24 hours without any issue... 
Everything seems very normal... But suddenly something happens and 
immediately the ldap server starts behaving very wierdly... The CPU 
usage for slapd hits 99.9% and it does not do any I/O at all... All 
parameters from iostat are just 0... So, it becomes completely CPU bound 
and pretty soon connections start piling up and eventually it starts 
refusing connections and at this point the server freezes up...

We did a strace and found that slapd was stuck in a futex... Has anyone 
seen this behaviour before...

The same thing happens when I do a query for all the nodes in the server 
too... Has anyone seen this kind of a behaviour?

Krish