[syslog-ng] [patch] only stat dns_cache_hosts file once in a second

[Balazs Scheidler]

On Wed, 2009-02-25 at 23:32 +0100, ILLES, Marton wrote:
> Hi,
> 
> I was doing today some performance tests where use_dns(yes) and
> persistent dns cache (dns_cache_hosts) were configured and I got awful
> results. When I disabled dns_cache_hosts the message rate doubled. After
> a quick check I realized that for every message a dns cache lookup was
> performed which stat()-ed my dns_cache_hosts file. However it does not
> make much sense to check the file for modification so often, I guess
> once a second is enough most of the cases.
> 
> In my test configuration I received msgs over syslog() source and sent
> to an empty destination. The server was a 2way quad-core 1.9GHz Opteron
> box running 32bit syslog-ng and messsages were generated with loggen.
> >From an average 80,000-90,000 msg/s using the fix I could do
> 220,000-230,000 msg/s. Interesting that on my laptop (dual-core 2.4GHz
> Intel 64bit) the performance gain was smaller from 90,000 to 100,000
> msg/s. I am still wondering about this big difference, specially because
> my laptop has higher frequency CPU...
> 
> Anyhow the patch could be found in my git repo, Bazsi please apply.
>   git://git.balabit.hu/marci/syslog-ng-3.0.git

Integrated as

commit 731a28515dffa4f5de09fd1de3b3c7b262fc6093
Author: ILLES, Marton <marci at balabit.hu>
Date:   Wed Feb 25 22:56:10 2009 +0100

    only stat dns_cache_hosts file once in a second and not at each lookup
    On my dual-core 2.4GHz x86_64 laptop it yields 10%
     while on an 2way quad-core 1.9GHz x86 Opteron server it yileds 100% gain

Thanks.
-- 
Bazsi