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From André Warnier ...@ice-sa.com>
Subject Re: [users@httpd] Re: excessive dns slows httpd
Date Tue, 04 Aug 2009 22:11:49 GMT
Mike -- EMAIL IGNORED wrote:
> On Tue, 04 Aug 2009 14:33:12 -0400, Mark H. Wood wrote:
> 
>> Local DNS cache of some sort on the Fedora box?  Some of my hosts run
>> 'nscd' (which comes with glibc) and some run BIND in cache-only mode.
> 
> Indeed there are two problems, and you nailed one of them:
> 
> 1. Both boxes have nscd, but it was not running on the CentOS
>    box.  Now that I fixed that, all but the first connection
>    are rapid, as you might expect.
> 
> 2. We still do not why the change in httpd.conf caused the
>    problem to appear.  However, my belief that there was a
>    difference between the two machines was probably incorrect.
>    When I tried it for the first time this morning, the box
>    that previously been fast was now slow.  No doubt, the
>    nscd storage had timed out.
> 
So, you still have DNS lookups of the clients happening.
If they are satisfied locally by some name server running on 127.0.0.1, 
you would not see them with wireshark, probably.
And when they are not in the cache, then it is probably nscd which does 
the DNS lookup elsewhere, not Apache.
Now the question remains of why these client lookups take place at all, 
even if they are often satisfied locally and fast.


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