Upgrade openldap, os and backend - pointers for best performance ?

Hi all,

I recently decided it was time for some upgrades, so I installed a new  
OpenLDAP server with the following changes:

		Old								New

os:		Ubuntu Hardy Server 32bit		FreeBSD 8.0-Release-p2
kernel:	32bit 2.6.24-24-server			32bit 8.0-Release-p2
fs:		XFS								UFS (soft-updates)
ldap:	2.3.37							2.4.21
bdb:	4.6.21-6							4.7.25.4

The rest is the same, dual 3.06Ghz P4 Xeon with only 4GB RAM. I'm  
using hdb as backend and have about 170k entries in the directory.  
Slapd configuration is the same. Oh and I'm only using syncprov overlay.

DB_CONFIG is the same on both machines, only containing this:

set_cachesize 0 268435456 1
set_lg_regionmax 262144
set_lg_bsize 2097152
set_lk_detect DB_LOCK_EXPIRE

On the new server, slapcat is faster, search returning single entry is  
slower, but search returning ~10k entries is faster (these are all  
second tries so cached data is used):

time ldapsearch filter=(uid=someusername) > /dev/null, returning one  
entry on localhost

old (on linux):

real	0m0.006s
user	0m0.000s
sys	0m0.000s

new (on freebsd):

real	0m0.033s
user	0m0.010s
sys	0m0.008s

---

time ldapsearch filter=(uid=a*) > /dev/null, returning ~10k entries on  
localhost

old (on linux):

real	0m1.728s
user	0m0.870s
sys	0m0.220s

new (on freebsd):

real	0m0.611s
user	0m0.074s
sys	0m0.015s

---

time slapcat > /dev/null

old (on linux):

real	0m26.834s
user	0m17.220s
sys	0m1.080s

new (on freebsd):

real	0m9.589s
user	0m8.884s
sys	0m0.699s

---

Now I know that too many variables have changed to point exactly at  
what's the reason for the speed changes, but does anyone else have  
experience with these version differences ? I need to be able to do  
about 100 searches/sec which will probably not be a problem, but I am  
curious whether someone has some pointers on how I can optimize for  
example some sysctl's, UFS mount settings, DB_CONFIG or something else  
on this new setup to get the best performance possible ?

Thanks a lot & kind regards,

Leon de Rooij
[email protected]


PS: Thanks to all the developers of OpenLDAP, I've been using it  
without any problems for a couple of years already and it rocks very  
much!