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From André Warnier ...@ice-sa.com>
Subject Re: [users@httpd] excessive dns slows httpd
Date Tue, 04 Aug 2009 06:22:14 GMT
Mike -- EMAIL IGNORED wrote:
> My web server is a CentOS box thus:
> 
>    [root ~]# uname -a
>    Linux mbrc21 2.6.18-92.1.22.el5 #1 SMP Tue
>       Dec 16 12:03:43 EST 2008 i686 athlon i386 GNU/Linux
>    root ~]# rpm -q httpd
>    httpd-2.2.3-22.el5.centos.2
> 
> My development and standby is on a Fedora box thus:
> 
>    [root ~]# uname -a
>    Linux mbrc32 2.6.23.17-88.fc7 #1 SMP Thu
>       May 15 00:35:10 EDT 2008 i686 athlon i386 GNU/Linux
>    [root@ ~]# rpm -q httpd
>    httpd-2.2.8-1.fc7
> 
> They are close neighbors on my LAN.
> 
> Now I recently revised my httpd.conf making it somewhat
> more complex and adding ssl for part of it.  Running the
> same configuration on both boxes, I find that the Fedora
> box runs rapidly, while the CentOS box is very slow.
> 
> Examining the situation with WireShark on both boxes I
> find that in responding to a simple GET, the CentOS box
> does a sequence of DNS queries to resolve the details of
> the location of the client IP address, whereas the
> Fedora box does no such thing.  It ts these DNS queries
> that are causing the slow response.
> 
> Now if I revert to the old configuration, there is no
> such problem and WireShark shows that there are no DNS
> queries.
> 
> Advice on how to proceed would be much appreciated.
> 
You could first check the obvious, such as whether in your Apache/Centos 
config, you are not *asking* the server to do these DNS lookups.
Look here for instance :
http://httpd.apache.org/docs/2.2/mod/mod_log_config.html#formats
(I mean that if your are asking Apache to log the *name* of the client 
in the access log for instance, then it has to do a lookup)
Any time, anywhere, where Apache, for whatever reason, has to translate 
an IP address into a name or vice-versa, may result in this behaviour.

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