dn cache size exceeds the limits

Hi,

During performance testing with SLAMD we noticed the dncache exceeds the limit. As a result the system
starts to swap a lot and the responses of slapd are very slow.

Has anyone seen that behavior before?

Here are the facts:

slapd.conf 
monitoring      on
tool-threads    4
cachesize       450000
dncachesize     450000
idlcachesize    450000
cachefree       90000

# ldapsearch -x -D "cn=xxxx" -w xx -b 'cn=database 2,cn=databases,cn=monitor' -s sub '(objectclass=*)'
'*' '+' | grep -i Cache

olmBDBEntryCache: 398306
olmBDBDNCache: 482001 <<==========
olmBDBIDLCache: 449999

# slapd -V
@(#) $OpenLDAP: slapd 2.4.11 (Sep 11 2008 10:58:58) $
        root <at> node3:/usr/src/redhat/BUILD/openldap-2.4.11/servers/slapd

#db_stat -V
Berkeley DB 4.6.21: (September 27, 2007)

# uname -r
2.6.9-67.ELsmp

# cat /etc/redhat-release
Red Hat Enterprise Linux AS release 4 (Nahant Update 6)

Cheers,
Pavlos