Scalability problem

I am using pam ldap module to interface to a directory service
containing identity information. My directory contains an very big
number of groups, in the order of some thousands. Sniffing the network
i see that a lot of gloabal searches ( reqeusts for all the groups in
the directory ) are sent toward the directory. This causes a lot of
network traffic and poses some awkard scalability problems. Is there
any way to avoid this kind of queries, or is there any way to solve
this scalability problem???
Thanks in advance,
Luca Regini.