Alright, just realized that the above query is the already improved query (takes 773 ms). here is the corresponding one in 2.0.3 which actually takes 5 sec:
select dotlrn_member_rels_approved.rel_id,
dotlrn_member_rels_approved.rel_type,
dotlrn_member_rels_approved.role,
dotlrn_member_rels_approved.user_id,
registered_users.first_names,
registered_users.last_name,
registered_users.email
from registered_users,
dotlrn_member_rels_approved,
dotlrn_communities
where dotlrn_communities.community_id = :subcomm_id
and dotlrn_communities.parent_community_id = dotlrn_member_rels_approved.community_id
and registered_users.user_id = dotlrn_member_rels_approved.user_id
and registered_users.user_id not in (select dm.user_id
from dotlrn_member_rels_full dm
where dm.community_id = :subcomm_id)
order by last_name
So now the page is served in 5 sec.
