I'd like to understand how indexes are used with search. I've found some info http://www.openldap.org/doc/admin24/tuning.html#Understanding how a search works http://www.openldap.org/doc/admin24/tuning.html#Understanding%20how%20a%20search%20works but that's not very precise.

Suppose there is a search like (&(attr1=value1)(attr2=value2)), attr1 and attr2 are indexed. As far as I understand, this search fetches objectIDs from the index on attr1, than the objectIDs from the index on attr2, than, according to operation "and" ("&"), objectIDs that present in BOTH sets are determined (using some set-intersection algorithm). When the search is "or" (|(...)(...)), the objectIDs from both sets are joined and duplicates are removed (using some set-union algorithm). If there is no index on attribute, the resulting objectID set is determined by bare iterate-and-compare on all the objects, or so. Am I right?

Could anyone advice some docs on this?