Re: [squid-users] Occasional slow connections/timeouts

> On 2014-02-21 06:10, Simon Beale wrote:
>> I've got a problem at the moment with our general squid proxies where
>> occasionally requests take a long time that shouldn't do. (i.e. 5+
>> seconds
>> or timeout, instead of milliseconds).
>>
>> This is most common on our proxies doing 100 reqs/sec, but happens
>> overnight too when they're running at 10 reqs/sec. I've got this
>> happening
>> with both v3.4.2 and also with a box I've downgraded back to v3.1.10.
>> For
>> v3.4.2, it's happening in both multiple worker and single worker modes.

As a follow up, we've narrowed this down to the internal DNS resolver.
When I deploy a 3.4.2 (which is what we're running elsewhere) that's been
recompiled with "--disable-internal-dns", the problem completely goes
away.

> What sort of CPU loading do you have at ~100req/sec?
> is that at or near your local installations req/sec capacity?

For the box running with a single worker, it consumes 50% of one core at
100 req/sec.
For the boxes running with 9 workers, each worker consumes 5% of a core at
the same rate.

>> The test is not reproducible, sadly, but I've got a cronjob running on
>> localhost on these boxes testing access times to various URLs covering:
>> HTTPS, non-HTTPS static content, using IP not hostname over both HTTP
>> and
>> HTTPS, and a URL on the same vlan as the proxies. All of these test
>> cases
>> have it happen occasionally, but not repeatedly/reliably.
>
> Some ideas:
> * DNS lookup delays ?

Yeah, when I enabled the dns resolution time logging in squid, that became
apparent.

Quite why the internal dns resolver shows this, but the external one
doesn't, I don't know. The DNS server query logs show both DNS servers in
/etc/resolv.conf getting the request in turn and answering it (though 5
seconds apart). It's happening for us in multiple datacentres, so is
unlikely to be port errors or internal packet loss.

It's only(/mostly?) apparent on our squid servers that do desktop
proxying, so do lots of DNS requests to everywhere; the squid servers that
handle just our datacentre servers don't show this problem, but only
really go to about 40 hosts in total.

Thanks

Simon
Received on Mon Feb 24 2014 - 13:12:17 MST