FW: Performance issue ( maybe ) corrected

Glenn Satchell glenn.satchell at uniq.com.au
Fri Sep 3 16:23:42 UTC 2010

On 09/04/10 01:36, Simon Hobson wrote:
> 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. 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.
> 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.

I'd check the network connection on the server for errors. Maybe a 
faulty cable, switch port or NIC? Perhaps auto-negotiation of speed or 
duplex is not correct?

The system looks to be very idle, and dhcpd doesn't impose much load.

Glenn Satchell                            |  Miss 9: What do you
Uniq Advances Pty Ltd, Sydney Australia   |  do at work Dad?
mailto:glenn.satchell at uniq.com.au         |  Miss 6: He just
http://www.uniq.com.au tel:0409-458-580   |  types random stuff.

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