On Mon, 2015-06-01 at 21:44 +0200, Reindl Harald wrote:
Am 01.06.2015 um 21:38 schrieb Andrew Lutomirski:
> On Mon, Jun 1, 2015 at 12:29 PM, Chris Adams <linux(a)cmadams.net> wrote:
>> Once upon a time, Andrew Lutomirski <luto(a)mit.edu> said:
>>> I'm with Jason here. Glibc's resolver is amazingly buggy, and
things
>>> break randomly and unreproducibly when this happens. A good setup
>>> would have a local resolver and glibc would be configured to cache
>>> nothing whatsoever. Then, if you need to perform maintenance on the
>>> local DNS cache, you can do it by flushing your local resolver rather
>>> than trying to figure out how you're going to persuade every running
>>> program to tell glibc to flush its cache.
>>
>> glibc doesn't have a cache, except each process caching the settings in
>> /etc/resolv.conf. That's part of the problem, because there's no way
to
>> cache "first server in resolv.conf is not responding", so each lookup
>> has to figure that out for itself (many timeouts).
>
> Glibc caches *something* that enabled the bug I hit. I don't know
> exactly what it's trying to cache, but it's certainly stateful
it don't cache dns respones - try it out in your local network
*client applications* may cache respones
try it out in your local network
* enter a non existing subdomain in firefox
* add the hostname to your LAN nameserver
* try again: firefox refuses
* restart just firefox
* it resolves without any delay
a) that proves no systemwide cachae
b) it proves with introduce a local systemdwide cache
you introduce a problem not existing before
If you have nscd running glibc caches, so it is a matter of
configuration.
The *only* reason why Firefox caches Names is because we do not have a
local dns caching resolver, so Firefox had to implement its own.
If you had a local caching resolver Firefox could be changed to stop
caching on its own instead. Which would be a plus, I often have way too
many tabs open to consider restarting firefox unless the website with
issues is really important. If i had a local resolver it would be easy
to just flush that one and have FF back in business immediately.
As you see it is a matter of perspective.
Simo.
--
Simo Sorce * Red Hat, Inc * New York