Interesting thing with DNS requests

[Fredrik Johansson]

Hi,
Thank you all for your helpfull answers!

torsdag 07 december 2006 09:45 skrev Thiago Macieira:
> Fredrik Johansson wrote:
> >torsdag 07 december 2006 04:26 skrev Pavel Troller:
> >> > How is requiring 15x as much data to do the same thing not a bug?
> >> > Both apps running in the same environment implies that this has
> >> > nothing to with the DNS server performance--the konqueror client
> >> > must be issuing far more DNS requests than the Firefox client.
>
> It is not a bug. The slowness you're experiencing is not caused by the
> extra DNS round-trips.

Actualy it did quite some improvement:
std. config			KDE_NO_IPV6=true	
~25 s				~12 s
656 DNS packets		176 DNS packets


std.config with nscd	KDE_NO_IPV6=true and nscd
~10 s				~8 s
24 DNS packets		0 DNS packets (been refreshing a while)


Turning javascript of and on didn't do much difference -1 s or so in both 
Konqueror and FF

8 s for Konq is very good (you could read the page after 4-5 s and it was 
loading image 14x of ~170 for over 2 s on all 5 refreshes)

Like always it is hard to tell the exact time as they differ on every request, 
(network latency, serverload etc)

>
> For whatever reason, kio_http isn't keeping those connections alive, so
> it's connecting way more often. And for each connect, there's DNS lookups
> (plural). There is a bug in glibc that causes extra, unnecessary lookups,
> though. Feel free to report it.

Report a bug in glibc about extra network requests, I do belive you, however I 
dont have the faintest idea about what the issue is, minimal reproducing code 
etc.
That wouldn't be a very constructive bug report, so without knowing why, what 
and when I wont report it to glibc.

>
> >> Hi!
> >>   Isn't it because KDE is by default trying IPv6 first when it detects
> >> that the machine is IPv6 enabled ? From my experiences, many DNSs
> >> still behave incorrectly on IPv6 (like AAAA or similar) queries so the
> >> additional traffic may be caused by this. Try to use tcpdump or
> >> wireshark to find, what your machine tries to query from the DNS.
>
> It isn't the case here. The symptom of broken IPv6 replies are things not
> being found or timing out, instead of taking long to render a page.
>
> >Also if that is the case shouldn't it try IPv6 once and if it fails go
> > for plain IP for future requests?
>
> It does. DNS works perfectly in that aspect. The nameserver caches the
> reply, but unfortunately it doesn't cache a no-reply for a field. I don't
> know if nscd does.

Well given that the DNS packets fell from 656 to 176 by setting KDE_NO_IPV6 
are you sure it is working? (Perhaps that was what you meant by the glibc 
bug)

>
> But, for the same reason we look up again, we don't cache anything in the
> KDE Libraries: we (I) simply don't want to implement DNS rules in KDE.
> You have daemons that do that way better than we could. So use them.

Ok it did wonders for me so you sold me, but distros include that as a std 
package?

Again thanks for your help!
/ Fredrik