This is a general LDAP tip and it applies to OpenDS the open source LDAP directory service in Java, as well as Sun Directory Server (all versions) and other LDAP servers:
How can I know the number of entries under a specific node of the Directory Information Tree ?
Well it’s simple. Every entry contains an operational attribute that specify the number of immediate subordinates entry : numSubordinates.
So to retrieve the number of entries under a specific node of the DIT, for example in the ou=people,dc=example,dc=com, a simple read is required.
$ bin/ldapsearch -p 3389 -D "cn=directory manager" -w – -b "ou=people,dc=example,dc=com" -s base ‘(objectclass=*)’ numsubordinates
Password for user ‘cn=directory manager’:
This attribute is defined in an expired Internet-Draft but has been well implemented in many servers. There are often some limitations, like the value only counts entries on the same server, but overall it’s a very useful attribute especially when browsing through the DIT.
OpenDS and Sun Directory Server also implements another attribute : hasSubordinates, defined in X.501. hasSubordinates is a boolean and returns "true" or "false" depending on whether the entry is a branch or a leaf in the Directory Information Tree.