Re: positive_dns_ttl

>
> Makes sense. In the current code, if the test for ttl == 0 is
> removed, it should set the '0' case to the negative TTL rather than
> the positive one, which would be better in all cases, I think.
>

Given that. I'd agree. However is negative-ttl limited to being 1 or more
itself?

Amos

>
> On 2007/10/11, at 3:06 AM, Duane Wessels wrote:
>
>>
>>
>>
>> On Wed, 10 Oct 2007, Mark Nottingham wrote:
>>
>>> From ipcache.c;
>>>
>>>> if (ttl == 0 || ttl > Config.positiveDnsTtl)
>>>> ttl = Config.positiveDnsTtl;
>>>> if (ttl < Config.negativeDnsTtl)
>>>> ttl = Config.negativeDnsTtl;
>>>> i->expires = squid_curtime + ttl;
>>>
>>> As I read this, if the TTL from an upstream resolver happens to be
>>> '0', it changes it to whatever positive_dns_ttl is -- even though
>>> that also acts as a ceiling for DNS TTLs.
>>
>> I think this is partly left over from the old days when Squid always
>> used the external dnsserver programs. 'dnsserver' could only report
>> TTLs if the O/S had the libresolv _dns_ttl hack. So "ttl == 0"
>> meant that dnsserver didn't have any TTL value, so it should be set
>> to positive_dns_ttl.
>>
>>> The problem is that this plays havoc with DNS-based load
>>> balancers, which will be '0' more often than other DNS entries by
>>> nature. Any chance of either;
>>
>> The only thing I'm worried about is that with true 0 TTL squid will
>> have to make multiple lookups for a single HTTP request. For
>> example, if someone had a long list of 'dst' ACLs then each one
>> could result in a new DNS lookup.
>>
>> AFAIK, the ipcache is the only place where DNS lookups are cached
>> and Squid may refer to the ipcache multiple times for a given HTTP
>> transaction.
>>
>> DW
>
> --
> Mark Nottingham mnot@yahoo-inc.com
>
>
>
Received on Wed Oct 10 2007 - 19:53:14 MDT