Dear Geert and mailinglist members,

> Thing I wonder about is how the cache size clipping was discovered.
I recently sent a SIGUSR1 to our dnsmasq because a user said that some
queries have continuously been answered NXDOMAIN although they
shouldn't. As they have been answered within less than a millisecond, I
thought it must be an issue with the cache. Make a long story short it
was their fault (an ordinary typo).

However, by chance, I found

May  4 18:06:13 dnsmasq[22952]: cache size 150, 2191/57999 cache
insertions re-used unexpired cache entries.

which seemed odd to me. I then looked at the man page and increased the
cache size limit to 100,000 in the config but the startup message told
me that the cache size is only 10,000. The way to the location where
this clipping is done wasn't long from here and I figured removing might
just be the best solution.

> I'm trying to tell that the performance penality that Simon warns us about, 
> might by canceled by high computing power.
I agree, but you should probably not be running a caching DNS server
with hundreds of active clients on a really low-power embedded machine
like the good old Raspberry Pi in its first version.
We have a dedicated (small) server for DNS, DHCP and email. dnsmasq is
able to handle DNS blazingly fast - even with a maximum cache size of
100,000 (I may even want to increase this further if it prevents
deletion of unexpired cache entries).

I'm just trying to make clear that removing this artificial limit may
improve the situation for those on beefier hardware but not impact the
others as they are responsible for what they set when they decide to
manually tweak their settings in this regard. It's a value where I think
the hand-holding dnsmasq is doing for possibly supporting embedded
devices better is just too much. In the end, Simon has to say if or not
this artificial clipping can be removed or not. I think yes, because it
doesn't affect anyone who has not changed the default value and allows
the others to use any value for cache size them deem right for their
hardware and application.

Best regards,
Dominik


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