FW: Performance issue ( maybe ) corrected
Bjarne Blichfeldt
bjb at jndata.dk
Fri Sep 3 16:26:53 UTC 2010
> -----Original Message-----
> From: Simon Hobson
> Sent: 3. september 2010 17:37
> To: Users of ISC DHCP
> Subject: Re: FW: Performance issue ( maybe ) corrected
>
> Bjarne Blichfeldt wrote:
>
> >During the problem I see something like (numbers added from memory):
> >Cpu0 : 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si,
> 0.0%st
> >Cpu1 : 0.3%us, 0.3%sy, 0.0%ni, 99.3%id, 0.0%wa, 0.0%hi, 0.0%si,
> 0.0%st
> >è Cpu2 : 0.0%us, 0.3%sy, 0.0%ni, 1.3%id, 98%wa, 0.0%hi, 0.0%si,
> 0.0%st
> >Cpu3 : 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si,
> 0.0%st
> >Mem: 2075208k total, 714656k used, 1360552k free, 189160k buffers
> >Swap: 4128760k total, 100k used, 4128660k free, 318604k cached
>
> ...
>
> >The next I have done is to increase default lease time from 8 hours to 5
> days.
>
> ...
>
> >1352 subnets
> >792 pools
> >around 7500 active leases
>
>
> That works out at one lease renewal every around
> 1.5 to 2 seconds, not exactly a heavy load.
I agree, and I have a hard time believing the machines are overloaded, there must be something else, but the traces...
> However, there are two things that can cripple
> the server under heavy I/O :
>
> Log files. Configure syslog to use async logs for
> whatever dhcp logs end up in. Otherwise, every
> discover, offer, request, and ack results in a
> wait while the log entry is synced out.
Excellent suggestion, I have done that now.
>
> Leases file. Again, every offer or ack is
> preceded by writing to the leases file. If the
> machine is liable to heavy I/O from other
> processes then it may be worth putting the leases
> file on it's own storage so dhcpd doesn't find
> itself stuck in an I/O queue.
Good suggestion, but unfortunately not immediately possible.
Thank you very much for your input.
regards,
Bjarne
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