pres indexes: do i need them?

[James Shvarts <ys2046@columbia.edu>]

Hi all,

i was hoping you will help me understand the "pres"ent indexes. i have 
an entry with the following format:

dn: uid=jsmith,ou=users,dc=myorg,dc=org
uid: jsmith
localUid: 223qadr42
userPassword: xxxx
cn: Test User
mail: jsmith@myorg.org
objectClass: top
objectClass: myPerson

i need to put an index on uid and localUid for faster searches. both 
attributes will always be present (if not, the application has major 
problems). the searches will always be based on equality and not on 
substring or soundex, etc. so my indexing options are:

index uid,localUid pres,eq
or
index uid,localUid eq

given that both attributes are used as "primary keys" and will always be 
present for each ldap user entry, do i benefit from adding "pres" index 
to them?
thanks a lot!

_james