[Mongrel] performance observation on redhat

Wayne E. Seguin wayneeseguin at gmail.com
Sun Sep 23 09:14:06 EDT 2007

On Sep 23, 2007, at 02:30 , armin roehrl wrote:
> Hi,
>     I made an interesting observation using webservers (not just  
> mongrel) under red hat enterprise
> linux ES release 4 (Nahant Update 5). Maybe this is helpful or  
> somebody with deeper networking
> expertise can comment on this.
> Once client said that 1-2% of the response of our server were  
> unacceptably slow (really huge 3s-21s).
> So I did more  ab and httperf tests and notice that very few  
> requests do take a very long time. Being clueless
> I first thought that the ruby garbage collector or mongrel is  
> causing the effect, so after looking
> at a similar setup using erlang's yaws or nginx alone, I noticed  
> that sometimes this can happen,
> especially when increasing the number of concurrent connects to a  
> large number (e.g. 250-500).
> I did the same on OS-X and did not notice these outliers.
> After a lot of painful searching by luck we found one cure:  
> inet_peer_threshold was too small.
> Chaging it to a much larger value made the problem go away.
> echo 500000 > /proc/sys/net/ipv4/inet_peer_threshold
> There is a trade-off here. A too small value causes too many delays  
> from inet-peer-storage cleaning
> and a too big value makes life well for some limited time, but when  
> it hits you, it becomes really expensive.
> Did you ever see this?
> Thanks,
>   -Armin


We might put this in the documentation, will discuss with the dev team.

Thank you for this.


Wayne E. Seguin
Sr. Systems Architect & Systems Administrator

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