After fiddling with enabled performance data, my Nagios (2.0rc2 on Redhat FC4) froze up for a few hours. It answered queries, but no service checks were performed for four hours. Had to kill and restart it. Found these entries in nagios.log:
 service_result_worker_thread(): poll(): EINTR (impossible)
I have in nagios.cfg:
I have a fair number of services (about 700). Weird, this has never happened to me before, in 5+ years of using Nagios. It is possible I started Nagios from the command line and forgot to background it, in which case I'm a big dummy. I'll report back if it happens again.