We test this by using the IP address, not the hostname.
What we can see is the extremely low speed of connection in 2 of 10 cases, when using a psql at command line with a simple "select 1 from...." inside a loop of a shell script FROM THE PG SERVER!!!
If we do the same, but using a pipe connection (no IP address), there is no delay.
Some of the Big Brains on this list might well have some better ideas...but...
I have to tell you how many times with how many products (Apache, PostgreSQL, MySQL, Lighttpd, Tomcat, the list goes on) I have been completely screwed by forgetting to check my DNS.
You might want to ensure that:
a) The PG server has DNS properly setup. Both forward and reverse.
b) Your test client is seeing the DNS records properly, both forward and reverse.
That might not be it, but I have lost many hours of my life to forgetting about that.
* Linux Centos 5 (2.6.18-406.el5.centos.plus kernel)
* max_connections: 800 (but never over 500. usually 300 to 400)
WE have detected randomly slow connections when accessing through the network (not at localhost)
We use a script with a loop calling the psql command running a simple "select 1 from table".
At localhost, the conection is a flash, showing in very few ms the result on screen.
When passing the parameter "-h" with its own IP addres it begin answering immediately, but suddenly it has a delay of 10 seconds or more to answer on 1 or 2 of 10 commands.
Our suspect is that ther is a problem with the network stack parameter, perhaps at kernel level.