wp-admin slow in multisite

Running WordPress 3.1.2 (newly updated, installed as 3.0 about a year ago) with subdomain multisite & using the Sunrise domain mapping plugin.

The frontend is fast, the backend (wp-admin) is very slow on the network admin site (www.example.com/wp-admin) but runs at “normal speed” on one of the subdomain backends (foo.example.com/wp-admin).

The server is our own, Ubuntu 10.04 with mod_security (which I’ve heard can slow things down).

Is there anything I can do to speed up the backend or run a trace somehow?

Solutions Collecting From Web of "wp-admin slow in multisite"

I ended up enabling WP_DEBUG and found an error – something about fsockopen() not being able to connect to my host (I didn’t write it down and now can’t reproduce it) – and found that it was a DNS issue;- my subdomain (foo.example.com) was resolving to the correct IP ( but the primary domain wasn’t.

I’m in the process of cloning & replacing a live server, external IP, internal IP; the new server has internal IP (different subnet) and the external IP is accessed via a second interface. Adding the correct DNS entry in /etc/hosts fixed the problem:    example.com     www.example.com