Re: [squid-users] Median response time high

Stig Rubinson wrote:
> Hi!
> This is my first mail in this group.
>
> I have recently set up a squid cahe for a network with 96 users in a
> remote area i Thailand. Our ADSL is poor and DNS servers are unreliable.
>
> Every day I get in cache.log "Median response time is..." The value is
> between 1001 and some 71 000 ms. Lots of lines.
>
> I have set up seven different DNS servers in the squid.config. How many
> can I write there, is there any limit?
>
> Running squid 2.6 under Debian.
>
> What can I do? Is there anything else I should check?
>
> /stig
>

There is no limit I know of. But keep in mind there are lag side effects
with having large numbers.

First is extra bandwidth usage: Squid sends one outbound packet + one
inbound packet, per DNS server, per lookup and only uses the fastest
result. Trading total response time for bandwidth.

Second is extra time spent both sending all those packets, then
verifying the responses are from safe source and if still needed.

Optimizations:

  * Make sure you are using the internal DNS resolver Squid provides.
It's vastly faster than the old dnsserver.

  * Increase the disk used for the cache (more hits, less external traffic).

  * Same for memory. Bandwidth+Speed vs Price.

  * On Linux use AUFS storage type, with COSS too for small objects if
you can. Both greatly reduce the disk access times.

  * Keep a close eye on the ACLs used. Make sure they are doing a little
external lookups and regex processing as possible.
(If you have may and need a hand optimizing, I'm available.)

  * Alter the refresh_patterns as needed to increase the number of HITS
you can provide. (reload-to-ims etc are particularly useful when
optimizing).

If possible, one further optimization is to setup a Squid outside the
trouble zone and use it as a parent. So that external peer does all the
DNS lookups and background work needed for retrieval. The local squid
only needs to maintain its link to the peer and cache as much as possible.

Creative use of DelayPools feature may also be a benefit. Providing fast
bandwidth for important things and slower speeds for luxuries.

Amos

-- 
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