DHCP restart with bulk lease data

[Sten Carlsen]

On 30-10-2019 11.59, Surya Teja wrote:

I was thinking that since it leaves the .<time> file present, it may have problems doing the file operations. 

I did some experimenting, whatever way I make the files write protected, dhcpd manages to change them back. The only thing I did not test is SELinux.

-------> Sten, can you suggest few steps to cross check on how to confirm that would be file operations issues when it has bulk data

What I did was to deliberately write-protect the files in various combinations including giving the /var/lib/dhcp a new owner and write protect it, then restart dhcpd. In my setup the file operations always finished with no visible delay or other hickups. I was a bit surprised as I did not expect dhcpd to be able to touch a write-protected file that it does not own.

On Tue, Oct 29, 2019 at 7:11 PM Sten Carlsen <[hidden email]> wrote:

On 29 Oct 2019, at 13.49, Surya Teja <[hidden email]> wrote:

Could there be issues with file permissions?
My guess is that the temporary file written can not be renamed because dhcpd does not have write permissions?   ------>

Hi Sten, I don't think it is with permission because after few minutes dhcpd is restarting and granting lease, the issue is it is taking long time,

I was thinking that since it leaves the .<time> file present, it may have problems doing the file operations. 

I did some experimenting, whatever way I make the files write protected, dhcpd manages to change them back. The only thing I did not test is SELinux.

In the isc dhcp forum I observed few options like  dont-use-fsync but it also suggest not recommended until thorough understanding OS 

I have installed the dhcpd on centos7, does any one have used this option? Any experience with it would be much helpful for me     

Thanks in advance

On Tue, Oct 29, 2019 at 6:12 PM Surya Teja <[hidden email]> wrote:

you're doing something wrong. With a decent disk subsystem this is expected to take a few *seconds* (5 - 10 seconds would be my estimate ) ---->

Hi  sthaug I don't see any disk subsystem issues, may be I am missing the cases, can you please suggest the areas or commands to cross check if possible?

Thanks Teja

On Tue, Oct 29, 2019 at 5:13 PM Sten Carlsen <[hidden email]> wrote:

> On 29 Oct 2019, at 11.20, [hidden email] wrote:
>
>> The main thing I am facing the issue is when the data is too high like
>> 50-60k leases in the file, the dhcpd service restart is taking more time
>> (nearly 5-6 minutes) some times nearly 10-11 mins
>
> If a dhcpd restart with 50 - 60k leases takes 5-6 minutes or more,
> you're doing something wrong. With a decent disk subsystem this is
> expected to take a few *seconds* (5 - 10 seconds would be my estimate
> based on what we see here with a larger leases file).

Could there be issues with file permissions?

My guess is that the temporary file written can not be renamed because dhcpd does not have write permissions?

>
> Steinar Haug, Nethelp consulting, [hidden email]
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