Re: Sharing DNS cache among Squid workers

On 14/01/11 11:20, Robert Collins wrote:
> On Fri, Jan 14, 2011 at 11:13 AM, Alex Rousskov
> <rousskov_at_measurement-factory.com> wrote:
>> On 01/13/2011 02:18 PM, Robert Collins wrote:
>>> Have you considered just having a caching-only local DNS server
>>> colocated on the same machine?
>>
>> I am sure that would be an appropriate solution in some environments. On
>> the other hand, sometimes the box has no capacity for another server.
>> Sometimes the traffic from 8-16 Squids can be too much for a single DNS
>> server to handle. And sometimes administration/policy issues would
>> prevent using external caching DNS servers on the Squid box.
>
> This surprises me - surely the CPU load for a dedicated caching DNS
> server is equivalent to the CPU load for squid maintaining a DNS cache
> itself; and DNS servers are also multithreaded?
>
> Anyhow, I've no particular objection to it being in the code base, but
> it does seem like something we'd get better results by not doing (or
> having a defined IPC mechanism to a single (possibly multi-core) cache
> process which isn't a 'squid'. [Even if it is compiled in the squid
> tree].
>
> -Rob

Thats pretty much my opinion too.

A shared resolver on the same box where possible is our best-practice
anyway. Where DNS speed is important users have their DNS as close as
possible to the Squid.

It maybe worthwhile instead researching the lightest available DNS
resolver and using that as a recommendation to assist people.

When the workers are doing shared memory blocks merging these caches
would be worthwhile to de-duplicate the entries. But until then its just
adding complexity.

Amos

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