[collectd] warning: tcpconns can be expensive

[James Byers]

We've been running collectd for years now on a few dozen boxes, and  
it's worked perfectly.  Recently we added the tcpconns module to watch  
a dozen or so ports and noticed a big spike in system CPU time on our  
webservers.  The hit was about 20% on a dual AMD 2216 running RHEL4  
and its stock 2.6.9 kernel with about 4000 tcp connections:

http://jbyers.com/cpu-collectd-tcpconns.png

The expense of inspecting a large /proc/net/tcp every 10 seconds looks  
like the cause.  Not suprising in hindsight, but it took us a little  
while to realize what was going on.  I don' t think there's anything  
to be done to collectd, but I thought this might be useful information  
for someone else in the future and might be a good warning to put on  
the tcpconns plugin page.

Thanks,
James
Wikispaces.com