Issue with huge numbers of connections

Norberto Meijome freebsd at
Tue Jun 19 13:58:05 UTC 2007

On Sun, 17 Jun 2007 19:06:16 +0100
Joe Holden <joe at> wrote:

> kern.ipc.nmbclusters

FWIW, this one in particular ( controls mbuf clusters) will made a huge
difference back in the FBSD 4 days on very heavily used websites. I've had them
tuned up to the order of almost 100K - over that they would lock up on boot -
the lock ups don't seem to happen anymore on 6, but YMMV.
BTW, when the servers I used to run experienced mbuf exhaustion, the machines /
OS would still be operational, but nothing would happen  at the network layer.
A reboot was the only solution I found at the time.

P Jeremy made a v. good point about the timeouts of the close states - bring
everything down to the minimum that makes sense to your app - the defaults are
horribly "kind" to lazy/slow clients :P

Service specific configurations may also affect how your resources are used
(for example, dont use HTTP keep alives as they hog priceless resources). I
know, pretty obvious, but might as well mention it.


{Beto|Norberto|Numard} Meijome

"But I don't have to know an answer. I don't feel frightened by not knowing
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which is the way it really is, as far as I can tell, possibly. It doesn't
frighten me." Richard Feynman

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