The syntax to specify LDAP authentication in pg_hba.conf seems to have changed between version 8.3 and 8.4. At least in Debian Squeeze, where I have both installed.
For 8.3, I had a line like this in pg_hba.conf:
host all all 192.168.44.0/24 ldap "ldap://localhost/dc=mydomain,dc=lan;uid=;,ou=People,dc=mydomain,dc=lan"
When trying to start 8.4 with the same line, I was getting
# /etc/init.d/postgresql restart 8.4 Restarting PostgreSQL 8.4 database server: main The PostgreSQL server failed to start. Please check the log output: [...] invalid authentication method ":ldap" [...] FATAL: could not load pg_hba.conf ... failed!
The new syntax which works in 8.4 is
host all all 192.168.44.0/24 ldap ldapserver=localhost ldapprefix="uid=" ldapsuffix=", ou=People, dc=mydomain, dc=lan"