Slow searches, bad index?

[David Smith <DavidSmith@byu.net>]

I have an OpenLDAP 2.0 directory full of about 5400 student user
accounts. I created a new objectclass with an optional StudentID field
(of type ...121.1.26, string). I have an entry in my slapd.conf like
this:

index studentid eq,sub

I ran slapindex -f /etc/openldap/slapd.conf, but my searches on
studentid are very very slow, while searches on uid are lightning quick.

Could this be because my StudentID field is optional in the ObjectClass?
Any other ideas to explain the slowness?

Thanks all,
Dave